Error numbers

 

C

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Error handling

Error codes

Error codes

errno

Assertions

assert

static_assert (C11)(removed in C23)

Bounds checking

set_constraint_handler_s (C11)

abort_handler_s (C11)

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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

Run this code

#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 <errno.h> (p: 205)

• C99 standard (ISO/IEC 9899:1999):

• 7.5/2 Errors <errno.h> (p: 186)

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

• 4.1.3 Errors <errno.h>

See also

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)
C++ documentation for Error numbers