4.8 ferror, ferror_unlocked—test whether read/write error has occurred

Synopsis

#include <stdio.h>
int ferror(FILE *fp);

#define _BSD_SOURCE
#include <stdio.h>
int ferror_unlocked(FILE *fp);

Description
The stdio functions maintain an error indicator with each file pointer fp, to record whether any read or write errors have occurred on the associated file or stream. Use ferror to query this indicator.

See clearerr to reset the error indicator.

ferror_unlocked is a non-thread-safe version of ferror. ferror_unlocked may only safely be used within a scope protected by flockfile() (or ftrylockfile()) and funlockfile(). This function may safely be used in a multi-threaded program if and only if they are called while the invoking thread owns the (FILE *) object, as is the case after a successful call to the flockfile() or ftrylockfile() functions. If threads are disabled, then ferror_unlocked is equivalent to ferror.

Returns
ferror returns 0 if no errors have occurred; it returns a nonzero value otherwise.

Portability
ANSI C requires ferror.

ferror_unlocked is a BSD extension also provided by GNU libc.

No supporting OS subroutines are required.