source: azure_iot_hub/trunk/musl-1.1.18/src/stdio/fflush.c@ 388

#include "stdio_impl.h"

/* stdout.c will override this if linked */
#ifndef __c2__
static FILE *volatile dummy = 0;
weak_alias(dummy, __stdout_used);
#else
extern FILE *volatile __stdout_used;
#endif

int fflush(FILE *f)
{
        if (!f) {
                int r = __stdout_used ? fflush(__stdout_used) : 0;

                for (f=*__ofl_lock(); f; f=f->next) {
                        FLOCK(f);
                        if (f->wpos > f->wbase) r |= fflush(f);
                        FUNLOCK(f);
                }
                __ofl_unlock();

                return r;
        }

        FLOCK(f);

        /* If writing, flush output */
        if (f->wpos > f->wbase) {
                f->write(f, 0, 0);
                if (!f->wpos) {
                        FUNLOCK(f);
                        return EOF;
                }
        }

        /* If reading, sync position, per POSIX */
        if (f->rpos < f->rend) f->seek(f, f->rpos-f->rend, SEEK_CUR);

        /* Clear read and write modes */
        f->wpos = f->wbase = f->wend = 0;
        f->rpos = f->rend = 0;

        FUNLOCK(f);
        return 0;
}

#ifndef __c2__
weak_alias(fflush, fflush_unlocked);
#else
int fflush_unlocked(FILE *f)
{
        return fflush_unlocked(f);
}
#endif