freebsd-dev/lib/libc/stdio/ferror.3

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.\"     @(#)ferror.3	8.2 (Berkeley) 4/19/94
.\" $FreeBSD$
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.Dd January 28, 2009
.Dt FERROR 3
.Os
.Sh NAME
.Nm clearerr ,
.Nm clearerr_unlocked ,
.Nm feof ,
.Nm feof_unlocked ,
.Nm ferror ,
.Nm ferror_unlocked ,
.Nm fileno ,
.Nm fileno_unlocked
.Nd check and reset stream status
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Ft void
.Fn clearerr "FILE *stream"
.Ft void
.Fn clearerr_unlocked "FILE *stream"
.Ft int
.Fn feof "FILE *stream"
.Ft int
.Fn feof_unlocked "FILE *stream"
.Ft int
.Fn ferror "FILE *stream"
.Ft int
.Fn ferror_unlocked "FILE *stream"
.Ft int
.Fn fileno "FILE *stream"
.Ft int
.Fn fileno_unlocked "FILE *stream"
.Sh DESCRIPTION
The function
.Fn clearerr
clears the end-of-file and error indicators for the stream pointed
to by
.Fa stream .
.Pp
The function
.Fn feof
tests the end-of-file indicator for the stream pointed to by
.Fa stream ,
returning non-zero if it is set.
The end-of-file indicator may be cleared by explicitly calling
.Fn clearerr ,
or as a side-effect of other operations, e.g.\&
.Fn fseek .
.Pp
The function
.Fn ferror
tests the error indicator for the stream pointed to by
.Fa stream ,
returning non-zero if it is set.
.Pp
The function
.Fn fileno
examines the argument
.Fa stream
and returns its integer descriptor.
.Pp
The
.Fn clearerr_unlocked ,
.Fn feof_unlocked ,
.Fn ferror_unlocked ,
and
.Fn fileno_unlocked
functions are equivalent to
.Fn clearerr ,
.Fn feof ,
.Fn ferror ,
and
.Fn fileno
respectively, except that the caller is responsible for locking the stream
with
.Xr flockfile 3
before calling them.
These functions may be used to avoid the overhead of locking the stream
and to prevent races when multiple threads are operating on the same stream.
.Sh ERRORS
These functions should not fail and do not set the external
variable
.Va errno .
.Sh SEE ALSO
.Xr open 2 ,
.Xr fdopen 3 ,
.Xr flockfile 3 ,
.Xr stdio 3
.Sh STANDARDS
The functions
.Fn clearerr ,
.Fn feof ,
and
.Fn ferror
conform to
.St -isoC .