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.

Defined in header `<errno.h>`
EDOM	Mathematics argument out of domain of function (macro constant)
EILSEQ (C95)	Illegal byte sequence (macro constant)
ERANGE	Result too large (macro constant)

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));
}

Possible output:

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

References

C11 standard (ISO/IEC 9899:2011):

7.5/2 Errors (p: 205)

C99 standard (ISO/IEC 9899:1999):

7.5/2 Errors (p: 186)

C89/C90 standard (ISO/IEC 9899:1990):

4.1.3 Errors

errno	macro which expands to POSIX-compatible thread-local error number variable (macro variable)
perror	displays a character string corresponding of the current error to `stderr` (function)
strerrorstrerror_sstrerrorlen_s (C11)(C11)	returns a text version of a given error code (function)

Error numbers

Contents

Error numbers

Notes

Example

References

See also