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#include "stdio_impl.h"
int ungetc(int c, FILE *f)
{
if (c == EOF) return c;
FLOCK(f);
/* Fail if unreadable or writing and unable to flush */
if ((f->flags & (F_ERR|F_NORD)) || (f->wpos && __oflow(f))) {
FUNLOCK(f);
return EOF;
}
/* Clear write mode */
f->wbase = f->wpos = f->wstop = f->wend = 0;
/* Put the file in read mode */
if (!f->rpos) f->rpos = f->rend = f->buf;
/* If unget buffer is already full, fail. */
if (f->rpos <= f->buf - UNGET) {
FUNLOCK(f);
return EOF;
}
/* Put a byte back into the buffer */
*--f->rpos = c;
f->flags &= ~F_EOF;
FUNLOCK(f);
return c;
}
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