Error numbers

Each of the macros defined in <errno.h> expands to an integer constant expression with type int and with a unique positive value. The following constants are defined by ISO C. The implementation may define more, as long as they begin with 'E' followed by digits or uppercase letters.

Notes

Many additional errno constants are defined by POSIX and by the C++ standard library , and individual implementations may define even more, e.g. errno(3) on Linux or intro(2) on BSD and OS X.

Example

#include <stdio.h>
#include <math.h>
#include <errno.h>
#include <string.h>
 
int main(void)
{
    errno = 0;
    printf("log(-1.0) = %f\n", log(-1.0));
    printf("%s\n\n",strerror(errno));
 
    errno = 0;
    printf("log(0.0)  = %f\n", log(0.0));
    printf("%s\n",strerror(errno));
}

log(-1.0) = nan
Numerical argument out of domain
 
log(0.0)  = -inf
Numerical result out of range

References