Difference between revisions of "c/preprocessor"
From cppreference.com
< c
m (→Capabilities) |
|||
| (4 intermediate revisions by 4 users not shown) | |||
| Line 7: | Line 7: | ||
* {{tt|#}} character | * {{tt|#}} character | ||
| − | * preprocessing instruction (one of {{tt|define}}, {{tt|undef}}, {{tt|include}}, {{tt|if}}, {{tt|ifdef}}, {{tt|ifndef}}, {{tt|else}}, {{tt|elif}}{{rev inl|since=c23|, {{tt|elifdef}}, {{tt|elifndef}}}}, {{tt|endif}}, {{tt|line}}, {{tt|error}}, {{tt|pragma}}) <ref>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. {{rev inl|until=c23|A common non-standard extension is the directive {{tt|#warning}} which emits a user-defined message during compilation.}}</ref> | + | * preprocessing instruction (one of {{tt|define}}, {{tt|undef}}, {{tt|include}}, {{tt|if}}, {{tt|ifdef}}, {{tt|ifndef}}, {{tt|else}}, {{tt|elif}}{{rev inl|since=c23|, {{tt|elifdef}}, {{tt|elifndef}}}}, {{tt|endif}}, {{tt|line}}{{rev inl|since=c23|, {{tt|embed}}}}, {{tt|error}}{{rev inl|since=c23|, {{tt|warning}}}}, {{tt|pragma}}) <ref>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. {{rev inl|until=c23|A common non-standard extension is the directive {{tt|#warning}} which emits a user-defined message during compilation.}}</ref> |
* arguments (depends on the instruction) | * arguments (depends on the instruction) | ||
* line break | * line break | ||
| Line 18: | Line 18: | ||
* '''{{rl | conditional | conditionally}}''' compile of parts of source file (controlled by directive {{tt|#if}}, {{tt|#ifdef}}, {{tt|#ifndef}}, {{tt|#else}}, {{tt|#elif}}{{rev inl|since=c23|, {{tt|#elifdef}}, {{tt|#elifndef}}}} and {{tt|#endif}}). | * '''{{rl | conditional | conditionally}}''' compile of parts of source file (controlled by directive {{tt|#if}}, {{tt|#ifdef}}, {{tt|#ifndef}}, {{tt|#else}}, {{tt|#elif}}{{rev inl|since=c23|, {{tt|#elifdef}}, {{tt|#elifndef}}}} and {{tt|#endif}}). | ||
* '''{{rl | replace}}''' text macros while possibly concatenating or quoting identifiers (controlled by directives {{tt|#define}} and {{tt|#undef}}, and operators {{tt|#}} and {{tt|##}}) | * '''{{rl | replace}}''' text macros while possibly concatenating or quoting identifiers (controlled by directives {{tt|#define}} and {{tt|#undef}}, and operators {{tt|#}} and {{tt|##}}) | ||
| − | * '''{{rl|include}}''' other files (controlled by directive {{tt|#include}}) | + | * '''{{rl|include}}''' other files (controlled by directive {{tt|#include}} {{rev inl|since=c23|and checked with {{c|__has_include}}}}) |
* cause an '''{{rl|error}}''' {{rev inl|since=c23|or '''{{rl|error|warning}}'''}} (controlled by directive {{tt|#error}}{{rev inl|since=c23| or {{tt|#warning}} respectively}}) | * cause an '''{{rl|error}}''' {{rev inl|since=c23|or '''{{rl|error|warning}}'''}} (controlled by directive {{tt|#error}}{{rev inl|since=c23| or {{tt|#warning}} respectively}}) | ||
| Line 44: | Line 44: | ||
===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc see cpp | cpp/preprocessor | Preprocessor | nomono=true}} | + | {{dsc see c|c/preprocessor/replace#Predefined macros|Predefined Macro Symbols|nomono=true}} |
| + | {{dsc see c|c/symbol index/macro|Macro Symbol Index|nomono=true}} | ||
| + | {{dsc see cpp|cpp/preprocessor|Preprocessor|nomono=true}} | ||
{{dsc end}} | {{dsc end}} | ||
{{langlinks|ar|cs|de|es|fr|it|ja|ko|pl|pt|ru|tr|zh}} | {{langlinks|ar|cs|de|es|fr|it|ja|ko|pl|pt|ru|tr|zh}} | ||
Latest revision as of 14:31, 22 June 2023
The preprocessor is executed at translation phase 4, before the compilation. The result of preprocessing is a 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,elifdef,elifndef(since C23),endif,line,embed(since C23),error,warning(since C23),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,#elif,#elifdef,#elifndef(since C23) and#endif). - replace text macros while possibly concatenating or quoting identifiers (controlled by directives
#defineand#undef, and operators#and##) - include other files (controlled by directive
#includeand checked with __has_include(since C23)) - cause an error or warning(since C23) (controlled by directive
#erroror#warningrespectively(since C23))
The following aspects of the preprocessor can be controlled:
- implementation defined behavior (controlled by directive
#pragmaand operator_Pragma(since C99)) - 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.(until C23)
[edit] References
- C17 standard (ISO/IEC 9899:2018):
- 6.10 Preprocessing directives (p: 117-129)
- C11 standard (ISO/IEC 9899:2011):
- 6.10 Preprocessing directives (p: 160-178)
- C99 standard (ISO/IEC 9899:1999):
- 6.10 Preprocessing directives (p: 145-162)
- C89/C90 standard (ISO/IEC 9899:1990):
- 3.8 PREPROCESSING DIRECTIVES
[edit] See also
| C documentation for Predefined Macro Symbols
| |
| C documentation for Macro Symbol Index
| |
| C++ documentation for Preprocessor
|
