Diagnostic directives - cppreference.com (original) (raw)

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

[edit] Syntax

[edit] Explanation

1. After encountering the #error directive, an implementation displays the message diagnostic-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

#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