errno

Global error variable

Synopsis:

#include <errno.h>

extern int errno;

Library:

libc

Description:

The errno variable is set to certain error values by many functions whenever an error has occurred.

It may be implemented as a macro, but errno can always be examined or set as if it were a simple integer variable. Values for errno are defined in the file <errno.h>, and include at least the following values:

Examples:

/*
 *  The following program makes an illegal call
 *  to the write() function, then prints the
 *  value held in errno.
 */
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

int main( void )
{
    int errvalue;

    errno = EOK;
    write( -1, "hello, world\n",
           strlen( "hello, world\n" ) );
    errvalue = errno;
    printf( "The error generated was %d\n", errvalue );
    printf( "That means: %s\n", strerror( errvalue ) );
}

Classification:

POSIX 1003.1

See also:

herrno(), strerror()