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      Diagnostic directives

      From cppreference.com
      <c‎ |preprocessor
       
       
       
       

      Shows the given error message and renders the program ill-formed, or given warning message without affect the validity of the program(since C23).

      Contents

      [edit]Syntax

      #errordiagnostic-message (1)
      #warningdiagnostic-message (2)(since C23)

      [edit]Explanation

      1) After encountering the#error directive, an implementation displays the messagediagnostic-message and renders the program ill-formed (the compilation stops).
      2) Same as(1), except that the validity of the program is not affected and the compilation continues.

      diagnostic-message can consist of several words not necessarily in quotes.

      [edit]Notes

      Before its standardization in C23,#warning has been provided by many compilers in all modes as a conforming extension.

      [edit]Example

      Run this code
      #if __STDC__ != 1#  error "Not a standard compliant compiler"#endif #if __STDC_VERSION__ >= 202311L#  warning "Using #warning as a standard feature"#endif #include <stdio.h> int main(void){printf("The compiler used conforms to the ISO C Standard !!");}

      Possible output:

      The compiler used conforms to the ISO C Standard !!

      [edit]References

      • C23 standard (ISO/IEC 9899:2024):
      • 6.10.5 Error directive (p: TBD)
      • C17 standard (ISO/IEC 9899:2018):
      • 6.10.5 Error directive (p: 126-127)
      • C11 standard (ISO/IEC 9899:2011):
      • 6.10.5 Error directive (p: 174)
      • C99 standard (ISO/IEC 9899:1999):
      • 6.10.5 Error directive (p: 159)
      • C89/C90 standard (ISO/IEC 9899:1990):
      • 3.8.5 Error directive

      [edit]See also

      C++ documentation forDiagnostic directives
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