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The C standard library is declared as a collection of header files. The C++ standard library is similar, but the declarations may be provided by the compiler without reading an actual file. C standard header files are named with a .h file name extension, as in #include <stdio.h>. Typically, custom C header files have the same extension. Custom ...
This directive, inserted at the top of a header file, will ensure that the file is included only once. The Objective-C language (which is a superset of C) has an #import directive, which works exactly like #include, except that it includes each file only once, thus obviating the need for #include guards. [3]
The application programming interface (API) of the C standard library is declared in a number of header files. Each header file contains one or more function declarations, data type definitions, and macros. After a long period of stability, three new header files (iso646.h, wchar.h, and wctype.h) were added with Normative Addendum 1 (NA1), an ...
windows.h is a source code header file that Microsoft provides for the development of programs that access the Windows API (WinAPI) via C language syntax. It declares the WinAPI functions, associated data types and common macros. Access to WinAPI can be enabled for a C or C++ program by including it into a source file: #include <windows.h>
In computer programming, a precompiled header (PCH) is a (C or C++) header file that is compiled into an intermediate form that is faster to process for the compiler.Usage of precompiled headers may significantly reduce compilation time, especially when applied to large header files, header files that include many other header files, or header files that are included in many translation units.
C does not have a notion of modules. However, separate object files (and hence also the translation units used to produce object files) function similarly to separate modules, and if a source file does not include other source files, internal linkage (translation unit scope) may be thought of as "file scope, including all header files".
But the preprocessor includes a file regardless of the extension. In fact, sometimes code includes .c or .cpp files. To prevent including the same file multiple times which often leads to a compiler error, a header file typically contains an include guard or if supported by the preprocessor #pragma once to prevent multiple inclusion.
The angle brackets surrounding stdio.h indicate that the header file can be located using a search strategy that prefers headers provided with the compiler to other headers having the same name (as opposed to double quotes which typically include local or project-specific header files).