[Xastir-Dev] Snapshot problem

[Derrick J Brashear]

Curt said:

> if ( system( command ) != 0 ) {
>            // We _may_ have had an error.  Check errno to make
>            // sure.
>            if (errno) {
>                fprintf(stderr, "%s\n", strerror(errno));
>                fprintf(stderr,
>                    "Failed to convert snapshot: %s -> %s\n",
>                    xpm_filename,
>                    png_filename);
>            }
>        }
>
>
> I did not see the "Failed to convert snapshot" message.  This means
> that ImageMagick's convert didn't return an error code in "errno"?
> Is ImageMagick not playing by the rules (again)?  I guess I'll add
> yet another error message to see if the system call is returning
> with an error.

No, that's legit. errno is set if system() fails, not if the command you
run returns non-zero.

>From system(3):
       The value returned is -1 on error (e.g. fork failed),  and
       the  return  status of the command otherwise.  This latter
       return status is  in  the  format  specified  in  wait(2).
       Thus,  the  exit  code  of  the  command will be WEXITSTA
       TUS(status).  In case /bin/sh could not be  executed,  the
       exit status will be that of a command that does exit(127).


So expect -1 and check errno, or greater than 0 and use WEXITSTATUS
(except on pre-posix systems but that's another story)