This documentation is copyright © 1998-2001 Sandro Sigala <sandro@sigala.it>.
All rights reserved.
Released under the GNU General Public License.
errno
Prototype
#include <errno.h>
#define errno implementation-defined
or
extern int errno;
Description
The errno
symbol holds the last error number set by several library
functions. It may be implemented as a macro or as an identifier with
external linkage. Please note that errno
value is set to zero only
at startup, and the user should set it to zero before a library
function call, then inspect it before a subsequent library function call.
Example
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
{
FILE *f;
/* Try to open an unexistent file. */
if ((f = fopen("noexist.txt", "r")) == NULL) {
fprintf(stderr, "Cannot open: error number %d: %s\n",
errno, strerror(errno));
return EXIT_FAILURE;
}
fclose(f);
return EXIT_SUCCESS;
}
References
ISO C 9899:1990 7.1.4