Diagnostic directives
Shows the given error message and renders the program ill-formed, or given warning message without affect the validity of the program(since C23).
# Notes
Before its standardization in C23, #warning has been provided by many compilers in all modes as a conforming extension.
# 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 !!");
}