This short term is well-known to everyone who has at least some experience with development. But not everyone understands what exactly it means and why it is needed. Developer Peter Gazarov talked about the API in simple words on your blog.

The abbreviation API stands for “Application Programming Interface” (application programming interface, application programming interface). Most large companies at some stage develop APIs for clients or for internal use. To understand how and how APIs are used in development and business, you first need to understand how the World Wide Web works.

World Wide Web and remote servers

The WWW can be thought of as a huge network of interconnected servers on which every page is stored. Regular laptop can be turned into a server capable of serving an entire website on the network, and local servers developers use it to create websites before making them available to the public.

When introduced into address bar browser www.facebook.com A corresponding request is sent to the remote Facebook server. Once the browser receives the response, it interprets the code and displays the page.

Every time a user visits a page on the web, they interact with the API remote server. The API is the component part of the server that receives requests and sends responses.

API as a way to serve clients

Many companies offer APIs as a ready-made product. For example, Weather Underground sells access to its weather data API.

Usage scenario: On the website of a small company there is a form for making appointments for clients. The company wants to integrate Google Calendar into it to give customers the ability to automatically create an event and enter details about an upcoming meeting.

API Application: The goal is for the site server to directly contact the Google server with a request to create an event with the specified details, receive Google's response, process it, and send the appropriate information to the browser, for example, a confirmation message to the user.

Alternatively, the browser can make a request to Google's server API without going through the company's server.

Than API Google Calendar different from the API of any other remote server on the network?

Technically, the difference is in the format of the request and response. To generate a full web page, the browser expects a response in HTML markup language, while the Google Calendar API will simply return data in a format like JSON.

If a request to the API is made by the server of a company's website, then it is the client (just as the browser is the client when the user opens the website).

Thanks to the API, the user gets the opportunity to perform an action without leaving the company’s website.

Most modern websites use at least a few third-party APIs. Many tasks already have ready-made solutions offered by third-party developers, be it a library or a service. It is often easier and more reliable to resort to a ready-made solution.

Many developers spread the application across several servers, which interact with each other when API help. Servers that perform a supporting function to the main application server are called microservices.

So, when a company offers an API to its users, it simply means that it has created a series of special URLs that return only data as a response.

Such requests can often be sent through a browser. Since HTTP data transfer occurs in text form, the browser will always be able to display the response. For example, through a browser you can directly access the GitHub API (https://api.github.com/users/petrgazarov), without an access token, and receive this response in JSON format:

The browser perfectly displays the JSON response, which can be inserted into the code. It is easy enough to extract data from such text to use it at your discretion.

Some more API examples

The word "application" can be used in different meanings. In the context of the API, this means:

• fragment software with a specific function,
• the entire server, the entire application, or just a separate part of the application.

Any piece of software that can be clearly distinguished from the environment can replace the letter “A” in an English abbreviation, and can also have some kind of API. For example, when a developer implements a third-party library into the code, it becomes part of the entire application. As a standalone piece of software, the library will have some kind of API that allows it to interact with the rest of the application code.

In object-oriented design, code is represented as a collection of objects. In an application, there can be hundreds of such objects interacting with each other. Each of them has its own API - a set public properties and methods for interacting with other objects in the application. Objects may also have private, internal logic that is hidden from the environment and is not an API.

API is short for Application Programming Interface. In general, every program, operating system, etc. has its own API. The Windows API consists of a number of functions that allow you to use Windows system constructs. All Windows API functions were written in C++, but your programs can easily use them from Visual Basic. API functions must be declared! The declaration of API functions has the following syntax:
Declare Function name Lib "libname" [()]

Keyword lib specifies in which library Visual Basic can find the desired function. This refers to dynamic link libraries (*.dll). But there is no need to specify the extension in aliasname. Alias ​​specifies under what name the program should look for a given function in the library. Arglist is the passed parameters. The Windows API allows two things: carrying out certain tasks and accessing system resources. You can view a list of various API functions and their declarations using the standard API Viewer program.

Windows APIs can be called from Visual Basic to perform tasks for which the standard one is not sufficient program code Visual Basic. For example, standards Visual tools Basic does not allow you to restart your computer. However, a reboot can be performed by calling the appropriate Window API function.

Note: If an API function expects a variable from you, you must Necessarily declare it and fill it with spaces. Those. the variable must be user defined. These are features of the C++ language, in which the Windows API was written.

Let's look at a couple of examples:

Let's say your application needs to determine the directory where the Windows 95/98/NT operating system is installed. The easiest way to do this is to use the GetWindowsDirectory API function.

1. In the module we declare the GetWindowsDirectory API function:

3. In the Main subroutine we enter:

Code

"The variable that needs to be passed to the API, we have already “we announced and now we fill in the blanks. "There should be approximately as many spaces as "approximately how many characters should the variable have. "In this case, 20 will be enough, since Windows is usually installed in " C:\Windows or C:\Win95, etc. That is, the sum of characters is more likely "the total will not exceed 20 WinDir = Space(20) Debug.Print Left(WinDir, GetWindowsDirectory(WinDir, 20)) "Since the API is a function, it should return some kind of "value. In this case, the GetWindowsDirectory function returns "the length of the sought value. That is, if, for example, the sought value " this is C:\WINDOWS, then the function will return the value 10. "The variable has a length of 20. These 10 characters are written "first, and then there are 10 spaces. Why do we, one might ask, "extra 10 characters? After all, this is using unnecessary memory... "Therefore, with the Left instruction we pull out from the WinDir variable "exactly as many first characters as are generally needed...

Second example:
For example, your program must determine which of your media is CD-ROM or remote, etc. The "native" Visual Basic toolkit does not allow you to do this - you have to resort to the GetDriveType API function.

1. In the module we declare the GetDriveType API function:

2. In the Main subroutine we enter:

This is what the GetDriveType function will return to us, for example, for me:
A: - 2
C: - 3
D: - 3
E: - 5
All other letters are marked with the number 1. Yes, to understand these designations you need to know the following table:

Constant name and value:
DRIVE_UNKNOWN 0
DRIVE_NO_ROOT_DIR 1
DRIVE_REMOVEABLE 2
DRIVE_FIXED 3
DRIVE_REMOTE 4
DRIVE_CDROM 5
DRIVE_RAMDISK 6

The Main subroutine in the module is like Form_Load on the form, i.e. is considered the main one and is loaded by default. Back

The purpose of many API functions can be easily guessed by their names. For example, GetWindowsDirectory (get the Windows directory) or GetDriveType (get the media type).

Answer taken from: www.mtsecurity.narod.ru

In order to make the work of their colleagues easier and to provide all Windows programs with a universal interface, Microsoft programmers created such a thing as an API - "Application Programming Interface".

This is a set of functions and procedures that can be most often used by programs: displaying a directory tree, searching for files, displaying a standard window with close, minimize and maximize buttons, and many others. As a result, a developer creating a program for Windows does not have to think through and develop special subroutines for displaying the program window, the window for selecting a folder and other similar elementary operations - he can simply call kernel32.dll or user32.dll from the libraries containing functions and procedures API, the function he needs, and she will do everything for him herself. There are many such functions and procedures - about 600.

In the MS-DOS operating system there was no such thing as an API - the one who undertook to write a program for this operating system was obliged to think through and implement methods for displaying images on the screen, receiving data from the user, from start to finish. traveling through the file system, drawing graphics, if such a possibility was necessary 2. This made the process of developing programs with a user-friendly interface a very labor-intensive process; often the time and effort spent on creating an acceptable graphical interface for the program exceeded the costs of implementing the program’s own algorithm, for which it was created. It is not for nothing that so-called “console” applications, that is, programs that work only from command line, without an interface - data was entered on the same command line or made from a file specified in it, and the results were output in simple text mode.

With the advent of the operating room Windows systems The backbreaking work of programmers to develop the appearance of the program and convenient ways to input and output information was greatly facilitated - API functions were already used in Windows 3.0. Now a programmer, if, for example, he wanted to create a text input window or a scroll bar, he only had to write a call to the function for displaying such a window with the parameters he needed, just like any other function of the language in which he wrote his program, and not to introduce huge amounts of code to create a program that re-draws such a window or bar (while being aware that when developing the next program that also uses such objects, he will have to develop such code again or try to partially use the old one, adapting it to the needs this new program). Therefore, the emergence of APIs made a revolutionary breakthrough in programming technology, allowing the creation necessary programs with the familiar convenient interface much faster, without worrying about such routine details as programming standard interface objects for input and output of information.

In the Visual Basic for Applications (VBA) language, many functions and API procedures are called themselves when the program is executed by the interpreter, so there is absolutely no need to use them to display text input and output windows, draw geometric shapes on the screen and other simple actions - VBA calls them as needed, and the program on it only needs to use the appropriate functions of this language. However, sometimes there is a need for certain actions for which either there are no analogues in the built-in VBA functions, or they work irrationally or too slowly. For example, a folder selection window with an image of a directory tree (Fig. 5.1) or a file search program (analogue in VBA functions - the "Application.FileSearch" object - works too slowly with large numbers of files). For such cases, VBA provides the ability to call API functions.

Unfortunately, the use of API functions in VBA is not documented in the help, so to learn how to use them you have to either look for books or online sources on office programming, or analyze the code of programs that contain calls to API functions.

In the vast majority of cases, when programming for Office, you can do without using the API, but sometimes just calling an API function can achieve the desired result. Let's say you need to ensure that different macros are called when you simply click a button on a panel with the mouse. Word tools and in the case of simultaneously pressing this button and the Shift or Control key. Here's a snippet of code doing this:

Declare Function GetAsyncKeyState Lib "user32.dll" (ByVal kState As Long) As Integer

GetAsyncKeyState(vbKeyShift Or vbKeyControl)

If GetAsyncKeyState(vbKeyShift) Then

Call macro1: Exit Sub

ElseIf GetAsyncKeyState(vbKeyControl) Then

Call macro2: Exit Sub

The first line is like “reserving” an API function for use in a VBA program. It can be seen that the GetAsyncKeyState function is called from the library (a file containing programs intended only for use by other programs) user32.dll, and the key number is passed to this function, and it returns an integer (namely 0, if the key with the corresponding number is not pressed, and -32767 or 1 if pressed). Any function or procedure called from non-VBA libraries must be so reserved using the Declare command.

The vbKeyShift phrase in the command is a substitute for the Shift key code (its value is 16), and vbKeyControl, as is easy to understand, is a substitute for the Control key code. The structure of the "If...Then" statements seems to be clear 3, but if not, look in the VBA help. The Call command before the macro name, as you remember, means launching it.

There are Russian sites on the Internet dedicated to API 4. Visit them to learn more about this feature set.

You've probably seen the term "API". Operating system, web browser, and application updates frequently announce new APIs for developers. But what is an API?

Application Programming Interface

The term API is an acronym and it stands for Application Programming Interface.

An API is like a menu in a restaurant. The menu contains a list of dishes that you can order, as well as a description of each dish. When you specify which menu items you want, the restaurant kitchen does the job and provides you with the finished dishes. You don't know exactly how the restaurant prepares this food, and you don't need to.

Likewise, the API provides many operations that developers can use, as well as a description of what they do. The developer does not need to know how, for example, the operating system is created and the Save As dialog box is displayed. They just need to know that it is available for use in the application.

This isn't a perfect metaphor as developers may have to provide their own API data to get results, so perhaps it's more like a fancy restaurant where you can provide some of your own ingredients for the kitchen to work with.

APIs allow developers to save time by leveraging platform implementation to get important work done. This helps reduce the amount of code to develop and also helps create consistency between applications on the same platform. APIs can control access to hardware and software resources.

APIs make life easier for developers

Let's say you want to develop an iPhone application. operating system Apple iOS provides a large number of APIs, just like any other operating system, to make this easier for you.

For example, if you want to embed a web browser to display one or more web pages, you don't have to program your own web browser from scratch just for your application. You
You can use the WKWebView API to embed a WebKit (Safari) web browser into your application.

If you want to take photos or videos from iPhone cameras You don't need to write your own camera interface. You can use the Camera API to embed the iPhone camera into your app. If the API didn't exist, app developers would have to create their own camera software and interpret camera hardware inputs. But Apple's operating system developers have done all that hard work, so developers can simply use the camera API to embed the camera and then continue writing their app. And when Apple improves the camera API, all apps that use it will automatically take advantage of that improvement.

This applies to all platforms. For example, do you want to create a dialog box in Windows? There is an API for this. Want to support fingerprint authentication on Android? There's an API for this, so you don't have to test every fingerprint sensor from every Android manufacturer. Developers don't have to reinvent the wheel over and over again.

APIs control access to resources

APIs are also used to control access to hardware devices and software features that the application may not have permission to use. This is why APIs often play a big role in security.

For example, if you have ever visited a website and seen a message in your browser that the website is asking for your exact location, that website is attempting to use the geolocation API in your web browser. Web browsers provide APIs to make it easy for web developers to access your location - they can simply ask "where are you?" and the browser will do the hard work of accessing your GPS or nearby Wi-Fi networks to find your physical location.

However, browsers also expose this information through APIs because access to it can be controlled. When a website wants to access your exact location, the only way to get it is through the location API. And, when a website tries to use it, you—the user—can allow or deny the request. Hardware resources such as a GPS sensor can only be accessed through an API, so the browser can control access to the hardware and limit what apps can do.

The same principle is used for modern mobile phones. operating systems, such as iOS and Android, where mobile applications have permissions that can be enforced by controlling access to the API. For example, if a developer tries to access the camera through the camera API, you can deny the permission request and the app will not have access to your device's camera.

File systems that use permissions, like Windows, Mac and Linux, have those permissions that are enforced by the API file system. A typical application does not have direct access to a raw physical hard drive. Instead, the application must access the files through the API.

APIs are used for communication between services

APIs are also used for other reasons. For example, if you have ever seen a Google Maps object embedded on a website, that website uses the Google Maps API to embed that map. Google provides APIs like these for web developers, who can then use the APIs to assemble complex objects directly on their website. If no such APIs exist, developers may have to create their own maps and provide their own map data to accommodate a small interactive map on the website.

And since it's an API, Google can control access to Google Maps on third party websites, ensuring that they use it in a consistent manner rather than trying to randomly implement the frame that the website is showing Google Maps, For example.

This applies to many different online services. There are APIs for requesting translation of text from Google Translate or display Facebook comments or tweets from Twitter on the website.

The OAuth standard also defines a number of APIs that allow you to log into a site through another service, such as using your Facebook, Google, or Twitter accounts to log into a new website without creating a new one. account user only for this site. APIs are standard contracts that define how developers interact with a service and the type of output that developers should expect to receive.

If you have read this article, you will have a better idea of ​​what an API is. Ultimately, you don't need to know what an API is unless you're a developer. But, if you see that a software platform or service has added new APIs for different hardware or services, it should be easier for developers to use such features.

Sooner or later, any programmer is faced with such a concept as API. However, when such a meeting occurs, not everyone knows what it is, why it is needed and how to use it. And in this article I am going to fill this gap in the knowledge of some of you, and also give an example from my practice.

API (application programming interface) - This application programming interface. More to the point in simple language, then this is a set various functions, constants, classes, query formats that can be used in other programs.

It can be considered that API- this is a certain object, the implementation of which we do not know, however, we can use it. For example, a computer is an object whose implementation very few people know, however, almost everyone can use it to perform some actions: watching videos, surfing the Internet, printing text, etc. Few people know how it all works, but almost everyone can do it.

Example API is Windows API, OpenGL API, Direct3D API and so on.

For example, not long ago I also encountered directly API. I registered for the mailing list service" SmartResponder.ru" and started a newsletter, which people began to subscribe to. The task was as follows: within 24 hours after subscribing, a person can purchase my paid video course at a discount. Since all information about subscribers is stored on the server " SmartResponder.ru", then normal access (for example, through DB) I did not have access to this data, but it was necessary to implement it. Thankfully, " SmartResponder.ru"have your own API, which I used.

I found in them API request format to get the subscription date as a result. Further through cURL I sent the corresponding request and received the required subscription date for a specific e-mail addresses. Next is standard processing and output of the result.