The explain_vfprintf_or_die function is used to call the
vfprintf(3) system call. On failure an explanation will be printed
to stderr, obtained from the explain_vfprintf(3) function,
and then the process terminates by calling exit(EXIT_FAILURE).
The explain_vfprintf_on_error function is used to call the
vfprintf(3) system call. On failure an explanation will be printed
to stderr, obtained from the explain_vfprintf(3) function,
but still returns to the caller.
fp
The fp, exactly as to be passed to the vfprintf(3) system call.
format
The format, exactly as to be passed to the vfprintf(3) system call.
ap
The ap, exactly as to be passed to the vfprintf(3) system call.
RETURN VALUE
The explain_vfprintf_or_die function only returns on success, see
vfprintf(3) for more information. On failure, prints an explanation
and exits, it does not return.
The explain_vfprintf_on_error function always returns the value
return by the wrapped vfprintf(3) system call.
EXAMPLE
The explain_vfprintf_or_die function is intended to be used in a
fashion similar to the following example: