Preprocessor
From cppreference.com
< c
The preprocessor is executed at translation phase 4, before the compilation. The result of preprocessing is single file which is then passed to the actual compiler.
Contents |
[edit] Directives
The preprocessing directives control the behavior of the preprocessor. Each directive occupies one line and has the following format:
-
#character - preprocessing instruction (one of
define,undef,include,if,ifdef,ifndef,else,elif,endif,line,error,pragma) [1] - arguments (depends on the instruction)
- line break
The null directive (# followed by a line break) is allowed and has no effect.
[edit] Capabilities
The preprocessor has the source file translation capabilities:
- conditionally compile of parts of source file (controlled by directive
#if,#ifdef,#ifndef,#else,#elifand#endif). - replace text macros while possibly concatenating or quoting identifiers (controlled by directives
#defineand#undef, and operators#and##) - include other files (controlled by directive
#include) - cause an error (controlled by directive
#error)
The following aspects of the preprocessor can be controlled:
- implementation defined behavior (controlled by directives
#pragma) - file name and line information available to the preprocessor (controlled by directives
#line)
[edit] Footnotes
-
↑ These are the directives defined by the standard. The standard does not define behavior for other directives: they might be ignored, have some useful meaning, or make the program ill-formed. Even if otherwise ignored, they are removed from the source code when the preprocessor is done. A common non-standard extension is the directive
#warningwhich emits a user-defined message during compilation.
[edit] See also
|
C++ documentation for preprocessor
|