It's early or late - any programmer comes across such concepts as API. However, if such a reaction arises, not everyone knows what it is, and it is necessary and how to vikorize it. And in this article, I am going to fill this gap in the knowledge of actions from you, and also I will apply my practice.

API (application programming interface) - tse application programming interface. In other words, in simple terms, there is a set of different functions, constants, classes, query formats that can be used in other programs.

You can tell me what API- this is some kind of object, the implementation of which we do not know, we can only vikorize it. For example, a computer is an object, the implementation of which very few people know, however, it can be explored in all sorts of ways: watching videos, surfing the Internet, other texts, etc. How everything works - few people know, but not everyone can work.

butt APIє Windows API, OpenGL API, Direct3D API And so on.

For example, recently I found myself stuck in the middle of API. I have registered for the postal service SmartResponder.ru And having launched the mailing list, people began to subscribe. The challenge has arrived: by reaching out and subscribing, people can get a low-cost video course. SmartResponder.ru", then primary access (for example, through DB) I don’t understand these data, but it was necessary to implement them. Thankfully, " SmartResponder.ruє your powerful API, Which is how I quickly became.

I know them API Enter the format to enter the prepayment date. Dali through CURL I have filled in the required entry and removed the required prepayment date for a specific e-mail address. The following is a standard procedure for processing and displaying the result.

What is the API?

• Lumber room *

I'm flying!
In this article, we will take a look at what an API is, how it is, and why it is used. Let’s also look at how the API can be used in your web applications and how you can make life easier for a programmer.

Well, let’s finish with the appointment. API (Application Programming Interface) – this is a programming interface, a creation program interface. As they say to my wiser, the API is a ready-made code to make life easier for the program. The API was created in order for the programmer to actually make it easier for other programs to write code (for example, functions). All knowledge of jQuery, writing in JavaScript, and also a kind of API. As you can see, jQuery makes it much easier to write code. Those that could be produced using basic JavaScript in 30 rows can be written using jQuery in 5-6. If you look at the API at a glance, you can find out a lot of services that can be developed. The most popular service today is code.google.com, which provides nearly hundreds of different APIs! This includes an interface for creating Android add-ons, various APIs for working with AJAX, and various API add-ons that can be easily adjusted to suit your needs.

How does it feel to write code with your own hands? Is it necessary to work on what has already been created? Is it possible to see cost-free solutions (and, in fact, cost-free help) from web development? If you answered “НІ” to this question, then please note that you have understood the essence of the API.

I still want to wash myself. The splinters should NOT bother with ready-made solutions, the fragments in the future will not interfere with the real tasks. So, if you are a novice programmer, then don’t vikorize the factory! Start thinking with your own head, there will be different algorithms to understand the essence of programming. I would also like to say that everyone is already convinced that the API is not a ready-made solution, but a middle ground, an interface for creating your own projects. You don’t eat frozen cutlets from the store? You should lubricate them right away, right? This analogy clearly depicts the essence of the API.

Zagalom, I found out what the API is, where and how it is used, most importantly for what. I hope you embrace the development of web programming and the understanding of ever greater depths!

Windows API - a set of operating system functions

The API abbreviation seems vague and confusing to many novice programmers. Actually, Application Programming Interface (API) is just a ready-made set of functions that can be used by add-on vendors. In the formal sense, this concept is equivalent to what was previously often called a library of subprograms. However, please note that under the API there is a special category of such libraries.

During the development process, a set of specific internal functions, which are required for the implementation of a particular program, is formed for the end user, which is called the MyApplication API. However, it is often discovered that these functions can be effectively used to create other programs, including other programs. In what way do the authors, based on the strategy of selling their product, choose nutrition: why do they allow access to which set for external customers? If confirmed, the description of the software package as a positive characteristic includes the phrase: “The package includes a comprehensive set of API functions” (or for additional money).

Thus, most often under the API there is a set of functions that are part of one program, but which are available for use in other programs. For example, Excel, in addition to the interface for the end user, has a set of Excel API functions that can be accessed, for example, with programs created using VB.

Apparently, the Windows API is a set of functions that is part of the operating system itself and at the same time is accessible to any other program, including one written using VB. This plan is completely analogous to the set of system BIOS/DOS overrides, which is actually the DOS API.

The advantage of the Windows API functionality, on the one hand, is much wider than that of DOS, on the other hand, it does not include many features for direct control of computer resources available to programs on the former OS. In addition, the connection to the Windows API is based on additional procedural parameters, and the DOS function is accessed through a special processor machine command called Interrupt.

The Most Required Win API for VB Programmers

Regardless of those that VB has no varied functions, in the process of more or less serious development it is revealed that their capabilities are often not sufficient to complete the necessary tasks. In this case, newbie programmers often begin to skimp on VB and think about changing the tool, not suspecting that their computer has a large set of costs and needs to enter them quickly.

When you get acquainted with the Win API, it turns out that there are a lot of used VB functions that are nothing more than expanded to specific system procedures, but only implemented in the same syntax as the given language. Based on the need for a quick API, the available options are:

1. API functions that are generally implemented in the form of VB functions. Time is no less, however, in which case it may be necessary to move to the API stagnation, so that it allows you to quickly increase productivity (except for the absence of unnecessary changes in the parameters that are transferred).
2. The created VB functions are implemented only as a result of the external API functions. Here's a simpler option. For example, the CreateDirectory API function has greater capabilities compared to the VB MkDir operator.
3. There are a large number of API functions that have no analogues in the current version of the VB language. For example, it is not possible to delete a directory using VB - for this you need to use the DeleteDirectory function.

It should also be noted that certain API functions (some of them in the Win API are even insignificant) cannot be accessed from VB programs through a number of language interfaces, for example, due to the lack of ability to work with memory addresses. However, in a number of cases, non-trivial programming techniques can help (in the case of the same addresses).

The author’s special idea is that instead of expanding the version to the version of the functions used by VB, the following would give a good description of the most common API functions. At the same time, I would like to please developers not to wait for the appearance of a new version for a feature with expanded functions, but rather to take into account the stock of the original Win API - it is completely clear that the capabilities you need could be implemented already in the version ї VB 1.0 release 1991.

Yak vivchati Win API

It’s not so easy to remember that the number of functions of the Win32 API is estimated at around 10 thousand (no one knows the exact figure, like Microsoft).

The VB warehouse (versions 4-6) includes a file with a description of the Win API - WIN32API.TXT (a report on its implementation will be announced later). Ale, in Persher, with a yogo, can be renounced the Vidomosti about the recognition of the same parameters for the vicoristovani mnemoni izmen, and in the other hand-the perepass of the functions of the tsomo file is far from gone. Nowadays (as luck would have it), VB 3.0 had special proof-of-concept files describing the Win16 API functions. In v.4.0, this valuable information is already available via the manual interface.

Additional information about the Win32 API can be found in the previous Platform Software Development Kit, which is also available on the MSDN Library CDs included with VB 5.0, 6.0 Enterprise Edition, and Office 2000 Developer Edition. However, finding the information you need there and accessing it is not at all easy. Without even mentioning that all the descriptions there are made entirely by C.

The world's most familiar introduction to API programming in VB environments is the book of the renowned American expert Daniel Appleman. This series of Dan Appleman's Visual Basic Programmer's Guide to Windows API (for Win16, Win32, hundreds of different versions of VB) since 1993 has consistently become a best-seller for VB programmers. The book Dan Appleman's VB 5.0 Programmer's Guide to the Win32 API, published in 1997, was brought to the author from the USA by a friend who knew about the first bookstore of a small provincial town.

This book, with over 1,500 pages, includes a description of the advanced techniques for API programming in VB, as well as more than 900 functions. The CD will contain the full text of the book and all software applications, as well as a number of additional sections that have not made it to the second version. In 1999, Dan Appleman released a new book, Dan Appleman's Win32 API Puzzle Book and Tutorial for Visual Basic Programmers, which includes overviews of another 7,600 functions (although not report boards).

Win API and Dynamic Link Library (DLL)

A set of Win API implementations as dynamic DLL libraries. Next we will actually talk about the technology of installing DLLs in the middle of VB in the application of libraries that are included in the Win API warehouse. However, when talking about DLLs, it is necessary to earn a lot of respect.

In this case, under the DLL, we can respect the traditional version of two-fold dynamic libraries, which ensures direct conversion to the required procedures - subprograms or functions (approximately the same as is expected when calling procedures in the middle of a VB project). Such libraries can be created using other tools: VC++, Delphi, Fortran, and VB (which appears in version 7.0) - the rest can only work using ActiveX DLLs, which can be accessed via the Internet OLE Automation face.

The dynamic library files may contain the extension.DLL, but this is not necessarily the case (for Win16 the extension.EXE was often stuck); Drivers of external devices are listed under the additional DRV.

As we have already mentioned, it is important to determine the exact number of Windows API functions and files so that they can be stored in the system catalogue. This plan would better see a library warehouse that goes up to the kernel of the operating system, and the main libraries with key additional functions.

And now I'm happy.

Please 1. Follow the correct formatting of the DL announcement L-procedures

The program's hierarchy down to DLL procedures looks the same as up to the "primary" Visual Basic procedures, for example:

Call DllName ([argument list])

However, to use external DLL functions (including the Win API), they must be called upon by the program using the Declare statement, which looks like this:

Declare Sub Procedure Name Lib _ “Library Name” _ [([List of Arguments])]

Declare Function Function Name _ Lib “Library Name” _ [([Argument List])]

Here, at the square arms, the necessary elements of the operator are indicated, the alternating words are shown in italics, and the key words are shown in italics. The advanced system has been designed to provide a good description of the operator syntax, which makes certain points less significant.

Most of the external functions are located in the General Declarations section of the module. If you place it in a form module, you must specify the Private keyword (this will only be available in the middle of the module) - this is the same for all procedures of the form module.

The set of Win32 API implementations is limited to functions (the Win16 API had a lot of Sub programs). This is especially true for functions of the Long type, which most often return the completion code of an operation.

The Declare operator appeared in MS Basic already for DOS, and was used to communicate internal procedures to the project. Visual Basic doesn't need this, since the declarations of internal procedures automatically describe their Sub and Function descriptions. Adapted from Basic/DOS, the new description must indicate the name of the library file, where the procedure is located. Wip API libraries are located in the Windows system directory; all that is required is a file name. If you are working on a DLL, you will need to write a new path to that file to be sure.

The description of the Declare operator takes up a lot of space and does not fit in one row near the code window. Therefore, we recommend that when writing programs, you should pay attention to any type of row transfer scheme, for example:

Declare Function GetTempPath _ Lib “kernel32” Alias ​​​​“GetTempPathA” _ (ByVal nBufferLength As Long, _ ByVal lpBuffer As String) As Long

And here all the main elements of the description of the different rows are described and it’s good to read.

Please 2. Be especially respectful when working with DLL functions

The use of the Win API and various DLL functions significantly expands the functional capabilities of VB and, most often, allows you to increase program productivity. However, the price to pay for the price is a reduction in the reliability of robotic programs, especially during the development process.

One of the most important advantages of the VB middleware is the reliability of the program development process: operating under the interpreter framework, the program code is theoretically impossible to break the Windows and VB robot. The programmer may not be very careful about the correctness of passing parameters to the function that is called - such errors will be easily detected by the interpreter itself, either during the process of translating the code, or during its execution. In the worst case scenario, there will simply be an interruption in the processing regime, both in terms of meaning, where and what happened.

The use of direct functions of the Windows API or other DLL libraries takes such control over the transfer of data and the process of concatenation to code outside the VB middle. Therefore, a compromise in external functions can lead to failure of both VB and the operating system. This is especially important at the stage of program development, if the presence of benefits is entirely natural. Thus, due to the wide range of functions of the base system, the programmer takes responsibility for the correctness of their implementation.

The problem is further complicated by the fact that different programs have different ways of passing parameters between procedures. (More precisely, different methods of transmission are subject to discussion, since many of us can support a number of methods.) Win API is implemented in C/C++ and we need to talk about passing parameters accepted in this system, as in are classified as the primary VB variant.

In connection with this, it should be noted that the appearance of VB analogues of API functions is justified by the adaptation of the remaining ones to the VB syntax and the implementation of a similar mechanism for controlling data exchange. We also appreciate that at the stage of final development of programs when building a module that is compiled, it is better to choose the compilation option P-code instead of Native Code (machine code). At first, the program operates under the control of an interpreter - rather than using machine code, but preferably by looking at the operating system and ensuring a manual mode for identifying possible errors.

Porada 3. Ten recommendations from Dan Appleman for reliable API programming in the VB middleware

Various functions of the API require more careful programming with the use of some not so basic methods of scaling up procedures (versus VB). In the future, we are gradually starving ourselves of this food. And now we’ll present a summary of Dan Appleman’s discussions on this topic (the first version appeared back in 1993) with some of our additional comments.

1. Remember about ByVal. The most common problem that occurs when an API and DLL is implemented before functions lies in the incorrect dictionary of the ByVal keyword: they either forget to put it, or, in the end, put it when there is no need for it.

These examples show the input of the ByVal operator to transfer parameters

Here it is worth mentioning that the transfer of parameters in any programming system, including VB, is determined by two main steps: sending (ByRef) or value (ByVal). The first option receives the address of the exchange (this option is used in VB for exchange), the other receives its value. The principle of validity lies in the fact that after an additional message it is ensured that the program that calls is returned to the changed value of the passed parameter.

To get started, conduct an experiment using the following programs:

Dim v As Integer v = 2 Call MyProc(v) MsgBox “v = “ & v Sub MyProc (v As Integer) v = v + 1 End Sub

Having launched the butt of Viconnya, vikamima, the values ​​of ZINSYAMS ZMINENE, RIVNE 3. On the right, in the Danim Vipad in the MyProc address, the addresses of the serpent v, fіzically shallow through the signs, the Viclikaє. Now change the procedure description to

Sub MyProc (ByVal v As Integer)

As a result, when you run the test, you remove v = 2, which means that the output value of the variable is passed to the procedure - the result of the operations that run on it is not returned to the program that calls. The value transmission mode can also be changed with the help of the Call operator as follows:

Sub MyProc (v As Integer) ... Call MyProc ((v)) '(v) - the arms indicate the transmission mode _ behind the values.

However, when expanding to internal VB-procedures, the use of the ByVal keyword in the Call statement is suppressed - instead of this, the round arms are blocked. Here's an explanation.

In the classic version (C, Fortran, Pascal), the importance of the ByRef and ByVal modes depends on what is placed on the data exchange stack - the exchange addresses or values. In Basic, the ByVal version of the software emulation has historically been used - the stack always contains addresses, except when passing the values ​​for which a time change is created. To distinguish between two options (Classic and Basic), there are different ways to describe the ByVal mode. It is imperative, the BYVAL in the VB regimen in the vb, forgetting the bunch of above the signs: overwhelming the shape of the beast, the program of the licheus, the viclika, turn around (abo does not turn) the vilennia of Zmіninov. In the “classical” version, such confusion can lead to a fatal death within the hour of the finalization procedure (for example, if instead of the memory address of the vikorist there are values ​​​​changeable, equal to, say, zero).

DLL functions are implemented according to “classical” principles and therefore require a clear description of how data is exchanged with each argument. This itself can serve as a declare function through the Declare description (more precisely, the list of arguments that are passed). Most often, passing parameters to a Windows API function or DLL is specified using the ByVal keyword. Moreover, it can be specified either in the Declare operator or directly when calling the function.

The legacy of incorrect parameter transfer is easy to transfer. If you select an obviously invalid address, you will see a GPF (General Protection Fault) notification. Since the function retrieves values ​​that escape a valid address, the API function enters a foreign area (for example, into the Windows kernel) with all sorts of catastrophic consequences that result.

2. Change the type of parameters that are being transferred. Equally important is the correct number and type of parameters that are passed. It is necessary that the arguments declared in Declare correspond to the parameters of the API function. The biggest problem with passing parameters is related to the difference between NULL and a row of zeros - the memory trace, which is one and the same.

3. Check the type of value that is being rotated.

VB is tolerant of setting up the diversity of types of values ​​that are rotated by the function, and some numeric values ​​are rotated through registers, and not through the stack. The following rules will help you determine the correct values ​​that are returned by the API function:

• A DLL function that does not rotate values ​​(analogous to void in 'C') may be dumbed down like VB Sub.
• An API function that rotates a value (Integer or Long), can be designated as either a Sub or a Function that rotates values ​​of a specific type.
• This API function does not rotate floating point numbers, but DLLs can rotate this type of data.

4. With great care, use the As Any construction. Many Windows API functions have the ability to accept parameters of different types and use them based on the As Any construct (the interpretation of the type depends on the meaning of other parameters that are passed).

Good solutions may have several aliases (Alias) functions in each case, two or more of them share the same functions, and each description has a parameter and singing type.

5. Don’t forget to initialize the rows. The Win API has a simple function that rotates information by collecting data from row buffers that are passed as a parameter. In your program, you can do everything correctly: don’t forget about ByVal, pass parameters to the function correctly. But Windows cannot believe how large the size of the storage space seen is. The size of the row must be sufficient to accommodate all the data that can be placed in it. The responsibility for reserving a buffer of the required size rests with the VB programmer.

Please note that in 32-bit Windows, with different rows, it is possible to convert from Unicode (double-byte encoding) to ANSI (single-byte encoding) and back, depending on the national system settings. Therefore, to reserve buffers, it is often safer to use byte arrays instead of regular ones. (A report about this will be discussed below.)

Most Win API functions allow you to set the maximum block size yourself. For example, you need to call another API function to indicate the size of the block. For example, GetWindowTextLength allows you to determine the size of the row required to place the title of the window contained by the GetWindowText function. For this reason, Windows guarantees that you will not go beyond the border.

6. Vikorize Option Explicit in both languages.

7. Carefully check the values ​​of the parameters and the values ​​that are being rotated. VB has the potential to verify types. This means that if you try to pass an incorrect parameter to a VB function, the worst that can happen is that you reject the error message from VB. Unfortunately, this mechanism does not work when upgraded to a Windows API function.

Windows 9x has a sophisticated system for checking parameters for most API functions. Therefore, the presence of a pardon in these data does not mean a fatal redress, but it is not so simple to determine what caused it.

Here you can find a number of ways to improve this type of milk:

• Check the skin adjustment mode or Debug.Print to check the skin response of the API function. Review the results of these clicks to ensure that everything is within normal limits and the function completed correctly;
• Vikorist the Windows developer of the CodeView type and the customized version of Windows (from the Windows SDK). These functions can detect the modification of parameters and most importantly determine which API function is to be modified;
• Check the additional features of third-party companies to verify the types of parameters and the acceptability of their values. Such methods can not only find parameter changes, but also tell the VB code where the change was made.

In addition, it is necessary to carefully check the result of the API function.

8. Remember that the numbers in VB and Windows are not the same. Let us first remember that the term “Integer” in VB means a 16-bit number, while in the Win 32 documentation it means a 32-bit number. In another way, integer numbers (Integer and Long) in VB are not values ​​without a sign (one digit is used as a sign, the other as a mantissa of a number), in Windows - even unknown numbers are used. This situation needs to be taken into account if you form a parameter using additional arithmetic operations (for example, calculating an address using additional substitution of a base and offset). For which standard VB arithmetic functions are not suitable. Why are you afraid of this situation, let’s talk about it.

9. Be careful with function names. In Win16, the names of all Win32 API functions are sensitive to the exact variation of minor and major letters (Win16 did not have this). If you are putting a small writer in place of a great one, then the required function will not be found. Also follow the correct suffix A or W in functions to set row parameters. (Report about this – div. below.)

10. Save the results of your work as often as possible. Failures associated with incorrect DLL and Win API scripts can lead to the crash of the VB middleware, and possibly the entire operating system. Please pay attention to ensure that your code is saved before the test run. The simplest thing is to set the mode for automatically writing modules to the project before starting the project in the VB environment.

After reading the previous one, you may be struck by the fact that the Win API function is removed from the right. By the way, this is true, but only in accordance with the safe programming that VB itself provides. However, in the case of mild stagnation and known possible pitfalls, this risk is minimal. In addition, it is often simply impossible to cope with the stagnation of the Win API - it will still be needed in case of serious development.

Before that, we previously thought about the “underwater” stones for a wide class of DLLs. With the Win API, everything is much simpler, since the form of implementation of these functions is clearly unified. Here are the main points to take into account the mother's respect:

1. Functions of the Win32 API are functions, or procedures of the Function type (the Win16 API had a lot of Sub programs). All functions are of type Long, so their descriptions are written in this form: Declare Function name ... As Long ‘function type _ is indicated in the explicit form

   Declare Function name& 'function type _ is indicated by additional suffix

   The conversion to the API function looks like this:

Result& = ApiName& ([ List of Arguments]

1. The most important function that is rotated is the operation completion code. Moreover, a non-zero value means normal completion, while a zero value means execution. Once again (or not before), you can clarify the nature of the amend by using the GetLastError function. The description of this function looks like this: Declare Function GetLastError& Lib “kernel32” ()

   UVAGA! At the Robot in the middle -faced VB for the ryannate of the valid Codes of the pardon, the vicoristovati power is powerful Lastdlleror Op'kta Err, the bb іnodi vene of the GetlasterRor function at the industrial of MIZh to the API vicuno viconun, the vicunks of the vicunomes of the fences.

   You can interpret the code that generates GelLastError using additional constants written in the API32.TXT file, with names that begin with the ERROR_ suffix.

   The most common types of attacks are the following codes:

   • ERROR_INVALID_HANDLE = 6& - incorrect handle
   • ERROR_CALL_NOT_IMPLEMENTED = 120& - call for Windows 9x functions available only for Windows NT
   • ERROR_INVALID_PARAMETER = 87& - incorrect parameter value

   However, there are plenty of functions to rotate the values ​​of a given parameter (for example, OpenFile rotates the values ​​of a file description). In this case, the value is assigned to some other special Return& values, most often 0 -1.

2. The Win32 API has strictly fixed methods for transferring the simplest types of data. a) ByVal...As Long

   At least 80% of argument passing is done with the Long type. Revise the argument first of all is accompanied by the ByVal keyword, and this, among other things, means that one-way data transfer is linked - from VB programs to an API function.

   B) ByVal...As String

   This type of transmission also tends to occur frequently, and with the same argument first of all ByVal gets stuck. When an API function is called, row addresses are written to the stack, allowing for two-way data exchange. When working in rows, it is necessary to take care of some problems.

   First, memory reservation for rows is carried out by the program that calls, so if the API function will store rows, it is necessary to create a row of the required size before calling it. For example, the GetWindowsDirectory function rotates the path to the Windows directory, which is not required to take up more than 144 characters. Evidently, the implementation of this function may look something like this:

   WinPath$ = Space$(144) ' reserve row in _ 144 character Result& = GetWindowsDirectory& (WinTath$, 144) _ ' buffer filling ' Result& - actual number of characters in the name _ directory WinPath$ = Left$(WinPath, Result&)

   Another problem lies in the fact that when an API function is converted to an API function, the output row is recreated on its internal display, and when exiting the function - in the same way. Just as in the early days of Win16 this operation required only the addition of a zero byte, for example, a row, then with the advent of Win32, the transformation of the double-byte encoding of Unicode into ANSI was achieved, and so on. (This was reported in the article “Features of robots with row changes in VB”, Computer Press 10'99 and 01'2000). It is only significant that with the help of the ByVal... As String construction it is possible to exchange rows of symbolic data.

   B) ... As Any

   This means that the value of the memory buffer address will be placed on the stack, the interpretation instead of what the API function will handle, for example, is independent of the meaning of other arguments. However, As Any can only be used in the Declare operator - when a specific function is applied, the argument may be assigned a specific value.

   D) ... As UserDefinedType

   Such a structure also often gets stuck when it is necessary to exchange data (the promise of the offending party) for the sake of some other structure. In fact, this design is a simple type of specific implementation of the As Any transmission form, it’s just that each function has a fixed structure.

   The form of the data structure is determined by a specific API function, and it is the responsibility of the program to correctly describe and reserve them with the same program. This is the design first of all vikorist without the words ByVal, then the transfer after sending is added to this box - the exchange address is written to the stack.

Butt up to the API function

This is illustrated by using the example of two basic functions of working with files - lopen and lread, which are described as follows:

Declare Function lopen Lib "kernel32" _ Alias ​​"_lopen" (_ ByVal lpFileName As String, _ ByVal wReadWrite As Long) As Long Declare Function lread Lib "kernel32" _ Alias ​​"_lread" (_ ByVal hFile As Long, lpBuff _ ByVal wBytes As Long) As Long

In VB, their analogues - sometimes more precise - are the Open and Get operators (for Binary mode). We are very impressed by the use of the Alias ​​keyword in the empty function - this is the very same problem, if you can’t do without it. These function names in the library begin with an under-chair symbol (typical style for movie C), which is not allowed by VB.

The operation of opening a file might look like this:

Const INVALID_HANDLE_VALUE = -1 ' invalid _ value description lpFileName$ = “D:\calc.bas” ' file name wReadWrite& = 2 ' read-write mode hFile& = lopen(lpFileName$, wReadWrite&) _ ' valued = INVALID_HANDLE _VALUE Then _ ' fix the file ' specify the fix code CodeError& = Err.LastDllError 'CodeError& = GetLastError _ ' this construction does not work End If

Here we must emphasize two points:

• As the value of the function we determine the value of the file description. The value confirms the value -1;
• In this case, it is not necessary to go to the GetLastError function - to retrieve the specified value of the error, we went to the Err object (we talked more about the possibility of such a situation).

Then you can read instead of the file, but it also conveys that the program is responsible for recognizing its structure (as is the case when working with multiple double files). In this case, the description of the lread function can look like this:

Dim MyVar As Single wBytes = lread (hFile&, MyVar, Len(MyVar) ' reading of the speech number, 4 bytes ' wBytes - number of data actually read, '-1 - parity... Type MyStruct x As Single i As Integer End Type Dim MyVar As MyStruct wBytes = lread (hFile&, MyVar, Len(MyVar)) ' read data structure, 6 bytes

Show respect once again: the other argument of the function is passed on to the senders, and to the return to the values.

Dim MyVar As String MyVar = Space$(10) ' reserve space for 10 characters wBytes = lread (hFile&, ByVal MyVar, Len(MyVar)) ' read character string, 10 characters

Here you can see the importance of the previously introduced butt - the row change is necessarily accompanied by the ByVal keyword.

Reading instead of a file in an array (for simplicity, we will use a single byte array) is compiled like this:

Dim MyArray(1 To 10) As Byte wBytes = lread (hFile&, MyArray(1), _ Len(MyArray(1))* 10) ‘ read 10 elements from the array

Specifying the first element of the array as an argument, we pass the address of the head of the memory area reserved for the array. Obviously, you can store any fragment of an array using this method:

WBytes = lread (hFile&, MyArray(4), _ Len(MyArray(1))* 5) reading array elements from 4th to 8th

Porada 5. Vickory Alias ​​for transfer Settings As Any

Here, based on the front butt, we reveal the essence of the fourth for the sake of Dan Appleman.

When working with the lread function, it is important to remember that when running an ordinary variable before it, it is necessary to use the ByVal keyword (otherwise the information about the illegal operation will not be lost). To be on the safe side, you can create an additional special description of this function for working only with common changes:

Declare Function lreadString Lib “kernel32” _ Alias ​​​​“_lread” (_ ByVal hFile As Long, ByVal lpBuffer As String, _ ByVal wBytes As Long) As Long

When working with this description, it is no longer necessary to indicate ByVal when printing:

WBytes = lreadString(hFile&, MyVarString, _ Len(MyVarString)) ‘

It would seem that the syntax of the Declare operator allows you to create such a special description for an array:

Declare Function lreadString Lib “kernel32” Alias ​​“_lread” (_ ByVal hFile As Long, lpBuffer() As Byte, _ ByVal wBytes As Long) As Long

Prote animal

WBytes = lreadArray(hFile&, MyArray(), 10)

inevitably lead to a fatal execution by the program.

This is a continuation of the discussion about the peculiarities of processing row changes Visual Basic: VB uses double-byte Unicode encoding, Win API - single-byte ANSI (and with a format accepted in C - with a zero byte at the end). It is obvious that when changing row changes as an argument, the conversion from Unicode to ANSI is automatically carried out when you call an API function (more precisely, a DLL function) and the conversion is carried out when rotated.

The bottom line here is simple: you can exchange symbolic data with the help of variable Strings, but they cannot be used to exchange sufficiently double information (as was the case when working with 16-bit versions of VB). It is better to use a one-dimensional byte array.

Apparently, the String type can be used to describe the structure of the structure. The connection with this memory is as follows:

• It is categorically not possible to use the following construction for the development of the Win API: Type MyStruct x As Single s As String

  In the order of the changeover, the row descriptor is passed along with all the inheritances in the appearance of the program.

• It is possible as a structure element of a row of fixed doubling: Type MyStruct x As Single s As String*8 ‘ row of fixed doubling End Type

In this case, be sure to re-create the code.

And respect remains: it is not possible to consolidate an array of row changes (both fixed and changeable) when upgraded to an API function at the same time. Otherwise, the emergence of an “illegal operation” will be guaranteed.

It is quite clear that you are in a bad situation if you need to write a DLL function to your library. The need will inevitably appear if you use mixed programming technology - a combination of two or more programs to implement one program.

It is significant in connection with the fact that mixed programming is the primary goal for implementation to achieve a comprehensive report. Indeed, the language language (more precisely, the programming system based on the language) has its strengths and weaknesses, so it is entirely logical to use the advantages of various tools to achieve various tasks. For example, VB - for creating a computer interface, C - for effective access to system resources, Fortran - for implementing numerical algorithms.

The author's idea is this: serious involvement in programming is emphasized by the developer using two tools. Obviously, in modern minds, it is very difficult to be an independent expert in two systems, which makes the “main and additional language” scheme more logical. The idea here is that bringing over the knowledge of the “additional” language (written to a number of simple procedures) can significantly advance the effectiveness of the “main” language. It is important that knowledge of VB, as an additional benefit, is now a practical requirement for a professional programmer. Before speaking, in just a few hours of DOS, for any programmer, let's look at Basic, it would be extremely important to know the basics of Assembler.

So it’s different, but in the minds of group robots, when the skin programmer is engaged in his own specific work, statements about the peculiarities of the procedural interface in different languages ​​are the fault of all participants in the project. I know that there are a lot of programming systems (including VB), in addition to the interface that needs to be explained, it is possible to establish other methods, extending the processing methods to procedures that allow you to adapt the interface to Other languages.

When using the interprocedural interface, be aware of the following possible pitfalls:

• Different languages ​​may be of interest to you about the rules for writing identifiers. For example, the alias sign of the name of the procedure, which is hidden in VB, is often used. This problem can easily be explained by the use of the Alias ​​keyword in the Declare operator (excellent example for 2.3).
• You can determine the sequence of writing arguments that are passed onto the stack. For example, in DOS hours (to be honest, I don’t know what it looks like in the Windows middle), writing down arguments from the end of the list, other languages ​​(Fortran, Pascal, Basic) – from the beginning.
• Various principles of transferring parameters - for instructions or meanings - are explained.
• Rigorous principles of preserving the rank and file. For example, in C (the same as in Fortran and Pascal), the end of a row is indicated by a zero byte at its end, and in Basic the end is written explicitly in the row descriptor. Obviously, it is necessary to remember the ability to change different codes of symbols.
• When transferring rich-world arrays, remember that there are different options for transforming rich-world structures on one-world (starting from the first index or from the rest, one hundred two-dimensional arrays - “in rows” or “in rows” to the little birds").

Based on this, the following recommendations can be formulated:

• Check out the simplest things by revising the way arguments are passed to a DLL function. The standards adopted for the Win API are entirely consistent.
• Every time, do not transfer masses of ordinary soldiers.
• Respectfully vikorist the transfer of simple ordinary and rich arrays.
• Be sure to carefully check the functionality of the mechanism for passing arguments to the procedure that is called and back. Write a special test to verify the data. Carefully check the correctness of the transfer of the skin argument. For example, if you have a procedure with many arguments, first check the correctness of passing the skin parameter for the option with one argument, and then for the entire list.

What does it do if the DLL function is already written, for example, in Fortran, but the input interface does not fit well with the new VB standard? Here you can give two dates. First: write a test DLL function and with its help, try using the trial and error method to select the required functionality for VB programs. Another: write an adapter procedure in Fortran that would provide a simple interface between VB and a DLL function with the transformation of simple data structures in a warehouse (for example, the transformation of a large byte array from a row array).

Otzhe: vykorist DLL functions. Also, save the sweetness.

ComputerPress 9"2000

Working with the API, you can feel both joy and disappointment at the same time. On the one hand, by interacting with other programs, you can greatly increase the audience retention and “wow-effect” of your program. Other than that, this includes reading tons of documentation, learning authentication strategies, and sifting through non-informative (or, well, random) notifications about amortizations.

First of all, if you still don’t fully understand what an API (Application Programming Interface) is, read the explanation in Skillcrush, and then the first part of this article so that you can use it.

"API" is an incredibly great concept - especially if your add-on is bundled with another add-on, it is not accessed through that API. Components in the middle of your own program, in other words, different parts of Rails, are also linked together through the API. They are also smaller independent subordinates that transmit data necessary for the skin to carry out specific power tasks. In the world of add-ons, everything is an API!

If you create programs with more dynamic frontend functionality (both single-sided Javascript add-ons and simple programs with side-by-side AJAX calls), they will connect to the Rails backend through your powerful API, which is really easy Danish pair-three rows of codes, What should you tell your controllers to use JSON or XML instead of HTML?

In this lesson you will learn how to create your own powerful API. In the upcoming lessons we will highlight how to interact with the API of other programs. Lessons can be a good springboard for learning the value of those, but they are unlikely to be able to completely cover all the consequences. Most of the work with the API means reading its documentation and figuring out what they want.

Points for reflection

Look at the instructions and see if you know the answers on them. Turn over to yourself again after the Victoire.

• As Rails understands, what type of file you will see when you force an HTTP request.
• Why is there a meta method for #respond_to?
• How do I rotate the user object (User) while specifying attributes that I don't want to include in that object (so you can't just rotate User.first)?
• Name 2 shortcuts that will be added to the #to_json method.
• How can I tell the controller that it is necessary to render the notification about the amend?
• How can I notify the authorities about the amends?
• Why can't you use session-based controller authentication methods if you want to allow programmatic connections to your API?
• What is “Service-oriented architecture”?

API Basics

Your Rails add-on is actually an API, although you might not think of it as an API. The web browser your client runs is also a program, so it actually sends an API request to your Rails add-on when the client opens a new page. We thought so because the rendering of HTML desktop templates is more extensive, so we simply embed this functionality into our server programs as a standard type of connection, and everything else is important.

However, often you want to earn money without having to deal with the headache of using a browser. You may not be interested in the page structure (HTML), but you just want to extract pure data. Let's say you want to remove the list of all successful clients. You can visit http://yourapplication.com/users to run the #index action and render a list of all your applications.

Why bother with all this information because all you want is to cancel the list of clients? The simplest option would be to send the request to the same URL, indicating the JSON or XML content type. Once you set up your Rails controller correctly, you end up with a simple JSON array object to accommodate all your users. Wonderful!

The same principle will stagnate if you use an external API. Let's say you want to undo the recent “tweets” of a koristuvach on Twitter. You only need to tell your Rails plugin how to interact with the Twitter API (to authenticate yourself), submit a query, and process the type of “replies” that will be returned.

Creation API

You may want to build your Rails utility by cleaning up the backend API for frontend web stories, or you might just want to learn how to write JSON if the frontend is asking for it. This section is not visible as you create a full-fledged RESTful API with authentication functions. This is smoothly introduced in connection with your addendum as an API.

Basics

If you want your Rails plugin to convert JSON instead of HTML, you will need to tell your controller to do so. The most miraculous thing is that one and the same controller can rotate different types in the sequence by running your computer from the browser or accessing the API through the command line. This means what type of request was made, based on the extension of the requested file, for example example.xml or example.json.

You can check what Rails “thinks” about the file type by checking the server log:

Started GET "/posts/new" for 127.0.0.1 at 2013-12-02 15:21:08 -0800 Processing by PostsController#new as HTML

The first row tells you what the request URL is, and the second row tells you where the requests are and how Rails processes them. Yakbi vi vikoristovali expanded.json , it would look like this:

Started GET "/posts.json" for 127.0.0.1 at 2013-12-04 12:02:01 -0800 PostsController#index as JSON

If you are running a test program, try querying different URLs. If your controller can't process them, you can disable the pardon, but still have to figure out what Rails understands about your requests.

Rendering JSON or XML

If you decide that you want to render JSON or XML instead of HTML, you will need to inform your controller that you need to render JSON or XML instead of HTML. One way to earn this is to use the #respond_to method:

Class UsersController< ApplicationController def index @users = User.all respond_to do |format| format.html # index.html.erb format.xml { render xml: @users } format.json { render json: @users } end end end

In this case, #respond_to transfers the object format to the block, until you can add a confirmation response to the rendering. You won't gain anything if you render HTML using a standard Rails template (in this application app/views/index.html.erb).

The #render function is useful to understand how to render a wide range of formats. If you pass the key: json, you will see #to_json on the value, in this application @users. This converts your Ruby object(s) into JSON rows that will be passed to the appendix that asks for it.

In this way, you will remove your API. Of course, the API creation can be more complex if you want to work on some non-routine speech, but keep everything down to the basics.

Indication of attributes that rotate

It’s possible that you want to reconnect, but don’t return the email address of the client at the same time as the user’s object (User). In this case you will want to change the attributes that will be rotated, modifying those that run the #to_json method.

Previously, you would simply rename the #to_json method with your version, but now you don’t need to - in fact, you will instead rename the #as_json method. The #as_json method is substituted for the #to_json method, so that its modification implicitly changes the result of #to_json, but does so in a specific way.

#to_json works in two ways: it runs #as_json and retrieves the hash of attributes that will be rendered in JSON. Then you can render using JSON using ActiveSupport::json.encode. Then, when modifying #as_json, you are more specifically telling the part of the #to_json method that you really want to change.

In our version, we need to modify #as_json in our model in such a way as to rotate the attributes that we don’t need:

# app/models/user.rb class User< ActiveRecord::Base # Вариант 1: Полное переопределение метода #as_json def as_json(options={}) { :name =>self.name ) # The email field is NOT included end # Option 2: Vikorist's standard method #as_json def as_json(options=()) super(only: [:name]) end end

Then, our controller will no longer need to render JSON as before (in the application below, JSON will always be rendered, regardless of whether the HTML query was sent or not):

# app/controllers/users_controller.rb class UsersController< ApplicationController def index render json: User.all end end

Please note that you do not need to click #to_json yourself if you are using #render - we can do this for you.

Heroku inodes can extract additional shortcuts for correct display of pages with corrections. Marvel. You may need to first remove static pages from the app/public directory.

Security calls

Perhaps you want to be able to access the API only for login purposes. Your authentication in the controller can already work for this robot - just check that you have the correct #before_action settings (for example, before_action:require_login). You may need functionality if you can view the side of the login, or you may be guilty of different data. You don’t want unlogged clients to be unable to access the API to retrieve important data. Likewise, you should not allow unauthorized users to display songs on your HTML page.

If you want to process requests from programs other than the browser (for example, from the command line), you cannot rely on browser cookies for authentication. In fact, most APIs provide power tokens as part of the authentication process. We'll talk a little more about tokens in the coming lesson.

The coming days

Now you have the skills to use your Rails program to output not only HTML, but also some other format. If you want to move forward and allow other vendors to use the resources of your platform (for example, so that they can use software instead of authentication as a customer), you will need to build up your API system most reliable. We will not highlight everything here, but rather marvel at the following materials:

• The article Building Awesome Rails APIs contains a description of the best approaches for the development of gaming applications and industry API standards.

Service-oriented architecture

The time has come to present an architectural approach under the name “Service-Oriented Architecture” (SOA). The main idea is that your income will be accumulated from anonymous services, payment system platform, customer registration, recommendation module, etc. Instead of doing everything in one head program, you break up the subsystems into independent units that interact one with another, vicariously through internal APIs.

This is good for many reasons. However, since your program doesn’t know how other parts work and only knows how to request data through their API, you can make changes to the service code and decide how to Vati, as before. You can completely replace one service with another, and as long as you communicate using the same API methods, everything will go even smoother. You can use external APIs as part of your programs (for example, payment systems) instead of writing it properly. You can create a PHP add-on that interacts with a Python add-on, that interacts with a Rails add-on, and all work together, even if they link to each other using an additional API.

As a rule, trying to keep your skin as free as possible with your program is a good idea. The concept of SOA encourages you to think in terms of what methods you want to give to other parts of your program, and at the same time make your code cleaner. Moreover, assuming that every major component of your program is independent, you will also be able to overcome problems much easier and make decisions more meaningful.

Developing a service-oriented architecture for an entire program is all about developing a giant collapsible Ruby script on a sophisticated class and method, or on a larger scale.

One of the most popular examples of the transition to service-oriented architecture is Amazon.com. Apparently in 2002, Jeff Bezos directly stated that all work groups must switch to SOA, otherwise they will be fired. Sumno Vidomy blog post Google's browser, for internal corporate purposes, and suddenly becoming open to the public by revealing Amazon's pressure on SOA. This is a wonderful read, so it’s easy to evaluate it, and the main points of Bezos’s sheet are included in the next quote from the post:

1) All commands now provide their data and functionality through service interfaces.

2) Commands are required to interact one with one through other interfaces.

3) Other forms of inter-process communication: the same direct messages, the same direct reading of data from another command, the same memory models, the same “backdoors”, etc. A single permissible method of interaction is access to the services interface through a boundary.

4) Whether the technology stinks. HTTP, Corba, Pubsub, power protocols - it doesn’t matter. I don’t blame Bezos at all.

5) All service interfaces, without blame, are designed with the ability to control calls. The team must plan and design in such a way as to be able to provide an interface to the developers of the company. Good blame.

6) Anyone who has ignored these disadvantages will be relieved.

SOA is not serious on the right side. Of course, there are a lot of problems that come with this wiki - marvel at this post about “taking away lessons” from Amazon - but it also has a lot of advantages.

You, of course, don’t worry about SOA while you’re creating “game” additions for yourself, but this food will definitely stand in front of you if you start working for an IT company, so getting to know it is a good practice.

Your meta

1. Read Section 7 of the Rails Controller Framework to learn about JSON and XML rendering.
2. The stinks are not difficult to look at (since they are a little far away, they are prepared at once), but if you like, take a look at Railscasts in the Additional Resources section at the bottom of the lesson to learn more about the API advantages.

Visnovok

We will do more with your add-on as an API during the Javascript course. In this course, you will create a number of full-stack add-ons that will use AJAX backends for a shorter backend interface, which actually includes rendering XML or JSON data instead of a full-fledged HTML page. Then you will create a bunch of one-sided Javascript add-ons that rely on the API provided by your Rails add-on to extract all the necessary data from the database, and otherwise, to process on the client side (in the browser).

The best way to interact with the API is to create and interact with it, which is what we focus on in our projects.

Perhaps you coined the term “API”. The operating system, web browser and updated programs often announce new APIs for consumers. What's an API?

Application Programming Interface

The term API is an abbreviation and stands for “Application Programming Interface”.

API tse yak menu in a restaurant. The menu contains a list of herbs that you can use, as well as a description of the skin herbs. If you indicate which menu items you want, the restaurant kitchen completes the work and prepares the food. You don’t know exactly how the restaurant prepares this food, and you don’t need it.

Likewise, the API provides a variety of operations that vikors can perform, as well as a description of what to do. The retailer needs to know how, for example, the operating system is created and the “Save” dialog box is displayed. They just need to know what is available for use in the supplement.

This is not an ideal metaphor, but some developers may have to give the API power to extract the results, which, perhaps, is more like a chimerical restaurant, where you can do things from your ingredients that the kitchen will produce.

APIs allow developers to save time by quickly using the platform's resources to earn a valuable job. This helps to change the amount of code that is broken down, and also helps to create compatibility between add-ons for the same platform. APIs can control access to hardware and software resources.

API makes life easier for retailers

Let's say you want to develop a program for the iPhone. The Apple iOS operating system provides a large number of API interfaces, like any other operating system, to make it easier for you.

For example, if you want to use a web browser to display one or several web pages, you do not need to program a web browser from scratch for your program. In and
You can use the WKWebView API to install a WebKit (Safari) web browser in your program.

If you want to take photos or videos from the iPhone camera, you do not need to write the camera interface. You can use the camera API to install an iPhone camera in your program. If there was no API, software developers would have to create the camera's own software and interpret the inputs of the camera's hardware. If the developers of the Apple operating system have developed all this important work for the robot, then the developers can simply use the camera API interface to add a camera, and then continue writing their programs. And if Apple improves the camera API, all programs that use it will automatically speed up these changes.

This applies to all platforms. For example, do you want to create a Windows dialog box? For whom is the API. Do you want to support fingerprint authentication on Android? For this API, you do not need to test the finger sensor of any Android vendor. Retailers do not need to repeat the wheel again and again.

API interfaces provide access to resources

APIs are also used to provide access to hardware devices and software functions that may not be allowed to be accessed by other programs. That's why APIs often play a big role in the marketplace.

For example, if you have ever visited a website and received notifications from your browser about the fact that the website is asking for your exact settings, this website is designed to use the geolocation API in your web browser. Web browsers are providing APIs to make it easy for web browsers to deny access to your data - they can simply ask “Where you are?”, and the browser will need to work with access to GPS or Wi-Fi connections to find your physical location. M_scescience.

However, browsers also provide this information via an API, so access to it can be controlled. If a website wants to deny access to your exact location, the only way to access it is through the extension API. I, if the website is trying to vikoristuvach yogo, you, koristuvach, can allow or edit this request. Access to hardware resources, such as a GPS sensor, is only possible through the API, so the browser can control access to the hardware and limit the capabilities of programs.

This same principle applies to current mobile operating systems, such as iOS and Android, where mobile programs have permissions that can be implemented by means of API access control. For example, if the user wants to deny access to the camera through the camera API, you can change the request for permission, and the program will not allow access to the camera of your device.

File systems that allow permissions, such as Windows, Mac and Linux, have permissions to set the file system API. A typical program does not have direct access to an unshared physical hard drive. In this case, the program can deny access to files via the API.

API is wikipedia for communication between services

APIs are also criticized for other reasons. For example, if you have ever downloaded a Google Maps object, you have sent it to a website, that website uses the Google Maps API to load that map. Google provides APIs similar to these for web browsers, who can then use the APIs to collect complex objects directly on their website. Since there are no such APIs, retailers may have to create and submit their own cards in order to place a small interactive map on a website.

Because of this API, Google can control access to Google Maps on third-party websites, ensuring that they will abuse it in a proper manner and not be tempted to recklessly leak the frame that the Google Maps website displays, for example.

There are a lot of different online services. Create an API to translate text from Google Translate or display Facebook comments or Twitter replies on websites.

The OAuth standard also defines a number of APIs that allow you to log into a site through another service, for example, using Facebook, Google, or Twitter account accounts to log into a new website without creating a new account account for that particular site. APIs are standard contracts that determine how retailers interact with the service, and the type of products that retailers are responsible for producing.

If you have read this article, then you will have the best statements about those such as APIs. By the way, you don’t need to know what an API is, since you’re not a developer. If you know that the software platform or service has added new APIs for various hardware or services, it may be easier for developers to use such functions.