ccan

Browse Source Download (without any required ccan dependencies)

Module:

noerr

Summary:

routines for cleaning up without blatting errno

Author:

Rusty Russell <rusty@rustcorp.com.au>

Description:

It is a good idea to follow the standard C convention of setting errno in your own helper functions. Unfortunately, care must be taken in the error paths as most standard functions can (and do) overwrite errno, even if they succeed.

Example:

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdbool.h>
#include <string.h>
#include <errno.h>
#include <ccan/noerr/noerr.h>

static bool write_string_to_file(const char *file, const char *string)
{
        int ret, fd = open(file, O_WRONLY|O_CREAT|O_EXCL, 0600);
        if (fd < 0)
                return false;
        ret = write(fd, string, strlen(string));
        if (ret < 0) {
                // Preserve errno from write above.
                close_noerr(fd);
                unlink_noerr(file);
                return false;
        }
        if (close(fd) != 0) {
                // Again, preserve errno.
                unlink_noerr(file);
                return false;
        }
        // A short write means out of space.
        if (ret < strlen(string)) {
                unlink(file);
                errno = ENOSPC;
                return false;
        }
        return true;
}

License: