Question

Code

printf("Doing functionname... ");
if (functionname(args) == -1)
{
    perror("functionname");
}
else
{
    printf("ok\n");
}

Expected behavior

Doing functionname… ok

OR

Doing functionname… functionname: Error blah blah

Actual behavior

However stderr and stdout are different output streams so the result looks like this,

functionname: Error blah blah

Doing functionname…

What are the possible workarounds?

Answer 1

Flush the output stream. stdout, by default, is line buffered; so the output is only effectivelly written when it sees a ‘\n’ (or when the buffer gets filled). By contrast, stderr is not buffered by default, so every single character is output immediately.

printf("blah blah blah");
fflush(stdout);

If you terminate the string with a ‘\n’, the stream will be flushed with no need for a specific fflush statement.

printf("blah blah blah\n"); /* stream flushed */

---

Alternatively, print your information stuff to the stderr stream

fprintf(stderr, "Doing functioname...");

This has the advantage that users may redirect all information messages to /dev/null