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).
Syntax
#error diagnostic-message
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(1) | ||||||||
#warning diagnostic-message
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(2) | (since C23) | |||||||
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.
Notes
Before its standardization in C23, #warning has been provided by many compilers in all modes as a conforming extension.
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 !!
References
- 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
See also
| C++ documentation for Diagnostic directives
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