Check if stderr is empty

Question

I write string to stderr by fprintf(strderr,format strimg, string) and later from other function I need to check if anything was written to stderr.

For this matter, is it ok to just check if stderr is empty? Or maybe ferror(stderr) will do the trick?

Afaik you can't check if stderr has been written to in any portable way. Couldn't you just break out the output to stderr to a separate function and set a boolean if it's ever called? — Joachim Isaksson, Mar 09 '12 at 13:14

score 1 · Answer 1 · answered Mar 09 '12 at 13:13

1

Probably better to use a boolean flag to track whether an error has been given or not - initialise it to false and set it to true any time you write to stderr. Then check that...

answered Mar 09 '12 at 13:13

JTeagle

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score 0 · Answer 2 · edited May 23 '17 at 12:12

0

have a look at this

in the comments, there's something about EOF, too. could be exactly what you're looking for?

edited May 23 '17 at 12:12

Community

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answered Mar 09 '12 at 13:41

sinned

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That's great for input files, not so useful for output. – JeremyP Mar 09 '12 at 14:14

score 0 · Answer 3 · answered Mar 09 '12 at 14:19

If you have the chance, do

#include <stdio.h>
#include <stdarg.h>
char errprintf_called = 0;
int errprintf(const char * fmt, ...)
{
    errprintf_called = 1;
    va_list ap;
    va_start(ap, fmt);
    int ret = vfprintf(stderr, ap);
    va_end(ap);
    return ret;
}

and use

errprintf("Error %d has occured!", 42);
if (errprintf_called) {
    whine();
} else {
    laugh();
}

Check if stderr is empty

3 Answers3