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The C preprocessor (used with C, C++ and in other contexts) defines an include directive as a line that starts #include and is followed by a file specification. COBOL defines an include directive indicated by copy in order to include a copybook. Generally, for C/C++ the include directive is used to include a header file, but can
In C and C++, the language supports a simple macro preprocessor. Source lines that should be handled by the preprocessor, such as #define and #include are referred to as preprocessor directives . Syntactic constructs similar to C's preprocessor directives, such as C# 's #if , are also typically called "directives", although in these cases there ...
The preprocessor replaces the line #include <stdio.h> with the textual content of the file 'stdio.h', which declares the printf() function among other things. This can also be written using double quotes, e.g. #include "stdio.h". If the filename is enclosed within angle brackets, the file is searched for in the standard compiler include paths.
Access to WinAPI can be enabled for a C or C++ program by including it into a source file: #include <windows.h> Also, the executable must be linked to each static library that either contains the function code or more commonly defines runtime, dynamic linking to a system dynamic link library (DLL).
For #include guards to work properly, each guard must test and conditionally set a different preprocessor macro. Therefore, a project using #include guards must work out a coherent naming scheme for its include guards, and make sure its scheme doesn't conflict with that of any third-party headers it uses, or with the names of any globally visible macros.
C standard library functions are exported from the C++ standard library in two ways. For backwards-/cross-compatibility to C and pre-Standard C++, functions can be accessed in the global namespace (::), after #include ing the C standard header name as in C. [42] Thus, the C++98 program
Using #pragma once allows the C preprocessor to include a header file when it is needed and to ignore an #include directive otherwise. This has the effect of altering the behavior of the C preprocessor itself, and allows programmers to express file dependencies in a simple fashion, obviating the need for manual management.
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.