In this article, we discuss Header File List And Functions In C Language. Header files contain the set of predefined standard library functions that we can include in our c programs. But to use these various library functions, we have to include the appropriate header files. Oct 18, 2019 Dev-C is a free full-featured integrated development environment (IDE) for programming in C and C. Written in Delphi and is bundled with, and uses, the MinGW or TDM-GCC 64bit port of the GCC as its compiler. It can also be used in combination with Cygwin or any other GCC-based compiler. C code files (with a.cpp extension) are not the only files commonly seen in C programs. The other type of file is called a header file. Header files usually have a.h extension, but you will occasionally see them with a.hpp extension or no extension at all.
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The header files for the Windows API enable you to create 32- and 64-bit applications. They include declarations for both Unicode and ANSI versions of the API. For more information, see Unicode in the Windows API. They use data types that enable you to build both 32- and 64-bit versions of your application from a single source code base. For more information, see Getting Ready for 64-bit Windows. Additional features include Header Annotations and STRICT Type Checking.
Visual C++ and the Windows Header Files
Microsoft Visual C++ includes copies of the Windows header files that were current at the time Visual C++ was released. Therefore, if you install updated header files from an SDK, you may end up with multiple versions of the Windows header files on your computer. If you do not ensure that you are using the latest version of the SDK header files, you will receive the following error code when compiling code that uses features that were introduced after Visual C++ was released: error C2065: undeclared identifier.
Macros for Conditional Declarations
Certain functions that depend on a particular version of Windows are declared using conditional code. This enables you to use the compiler to detect whether your application uses functions that are not supported on its target version(s) of Windows. To compile an application that uses these functions, you must define the appropriate macros. Otherwise, you will receive the C2065 error message.
The Windows header files use macros to indicate which versions of Windows support many programming elements. Therefore, you must define these macros to use new functionality introduced in each major operating system release. (Individual header files may use different macros; therefore, if compilation problems occur, check the header file that contains the definition for conditional definitions.) For more information, see SdkDdkVer.h.
The following table describes the preferred macros used in the Windows header files. If you define NTDDI_VERSION, you must also define _WIN32_WINNT.
The following tables describe other macros used in the Windows header files.
Setting WINVER or _WIN32_WINNT
You can define these symbols by using the #define statement in each source file, or by specifying the /D compiler option supported by Visual C++.
For example, to set WINVER in your source file, use the following statement:
#define WINVER 0x0502
To set _WIN32_WINNT in your source file, use the following statement:
#define _WIN32_WINNT 0x0502
To set _WIN32_WINNT using the /D compiler option, use the following command:
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cl -c /D_WIN32_WINNT=0x0502source.cpp
For information on using the /D compiler option, see /D (preprocessor definitions).
Note that some features introduced in the latest version of Windows may be added to a service pack for a previous version of Windows. Therefore, to target a service pack, you may need to define _WIN32_WINNT with the value for the next major operating system release. For example, the GetDllDirectory function was introduced in Windows Server 2003 and is conditionally defined if _WIN32_WINNT is 0x0502 or greater. This function was also added to Windows XP with SP1. Therefore, if you were to define _WIN32_WINNT as 0x0501 to target Windows XP, you would miss features that are defined in Windows XP with SP1.
Controlling Structure Packing
Projects should be compiled to use the default structure packing, which is currently 8 bytes because the largest integral type is 8 bytes. Doing so ensures that all structure types within the header files are compiled into the application with the same alignment the Windows API expects. It also ensures that structures with 8-byte values are properly aligned and will not cause alignment faults on processors that enforce data alignment.
For more information, see /Zp (struct member alignment) or pack.
Faster Builds with Smaller Header Files
You can reduce the size of the Windows header files by excluding some of the less common API declarations as follows:
Related topics
A header file is a file with extension .h which contains C function declarations and macro definitions to be shared between several source files. There are two types of header files: the files that the programmer writes and the files that comes with your compiler.
You request to use a header file in your program by including it with the C preprocessing directive #include, like you have seen inclusion of stdio.h header file, which comes along with your compiler.
Including a header file is equal to copying the content of the header file but we do not do it because it will be error-prone and it is not a good idea to copy the content of a header file in the source files, especially if we have multiple source files in a program.
A simple practice in C or C++ programs is that we keep all the constants, macros, system wide global variables, and function prototypes in the header files and include that header file wherever it is required.
Include Syntax
Both the user and the system header files are included using the preprocessing directive #include. It has the following two forms −
This form is used for system header files. It searches for a file named 'file' in a standard list of system directories. You can prepend directories to this list with the -I option while compiling your source code.
This form is used for header files of your own program. It searches for a file named 'file' in the directory containing the current file. You can prepend directories to this list with the -I option while compiling your source code.
Include Operation
The #include directive works by directing the C preprocessor to scan the specified file as input before continuing with the rest of the current source file. The output from the preprocessor contains the output already generated, followed by the output resulting from the included file, followed by the output that comes from the text after the #include directive. For example, if you have a header file header.h as follows −
and a main program called program.c that uses the header file, like this −
the compiler will see the same token stream as it would if program.c read.
C++ Header Files ExampleOnce-Only Headers
If a header file happens to be included twice, the compiler will process its contents twice and it will result in an error. The standard way to prevent this is to enclose the entire real contents of the file in a conditional, like this −
This construct is commonly known as a wrapper #ifndef. When the header is included again, the conditional will be false, because HEADER_FILE is defined. The preprocessor will skip over the entire contents of the file, and the compiler will not see it twice.
Computed Includes
Sometimes it is necessary to select one of the several different header files to be included into your program. For instance, they might specify configuration parameters to be used on different sorts of operating systems. You could do this with a series of conditionals as follows −
Header File In C
But as it grows, it becomes tedious, instead the preprocessor offers the ability to use a macro for the header name. This is called a computed include. Instead of writing a header name as the direct argument of #include, you simply put a macro name there −
Dev C++ Header Files List Windows 10
SYSTEM_H will be expanded, and the preprocessor will look for system_1.h as if the #include had been written that way originally. SYSTEM_H could be defined by your Makefile with a -D option.
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