125 lines
3.7 KiB
Groff
125 lines
3.7 KiB
Groff
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.\" $NetBSD: fread.3,v 1.14 2009/01/11 02:46:29 christos Exp $
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.\"
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.\" Copyright (c) 1990, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Chris Torek and the American National Standards Committee X3,
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.\" on Information Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)fread.3 8.2 (Berkeley) 3/8/94
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.\"
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.Dd December 19, 2008
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.Dt FREAD 3
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.Os
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.Sh NAME
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.Nm fread ,
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.Nm fwrite
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.Nd binary stream input/output
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdio.h
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.Ft size_t
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.Fn fread "void * restrict ptr" "size_t size" "size_t nmemb" "FILE * restrict stream"
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.Ft size_t
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.Fn fwrite "const void * restrict ptr" "size_t size" "size_t nmemb" "FILE * restrict stream"
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.Sh DESCRIPTION
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The function
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.Fn fread
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reads
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.Fa nmemb
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objects, each
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.Fa size
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bytes long, from the stream pointed to by
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.Fa stream ,
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storing them at the location given by
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.Fa ptr .
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.Pp
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The function
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.Fn fwrite
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writes
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.Fa nmemb
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objects, each
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.Fa size
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bytes long, to the stream pointed to by
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.Fa stream ,
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obtaining them from the location given by
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.Fa ptr .
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.Pp
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Mixing
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.Fn fread
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and
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.Fn fwrite
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calls without setting the file position explicitly using
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.Fn fsetpos
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between read and write or write and read operations will lead to unexpected
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results because of buffering the file pointer not being set to the
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expected position after each operation completes.
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This behavior is allowed by ANSI C for efficiency and it will not be changed.
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.Sh RETURN VALUES
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The functions
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.Fn fread
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and
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.Fn fwrite
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advance the file position indicator for the stream
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by the number of bytes read or written.
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They return the number of objects read or written.
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If
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.Fa size
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or
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.Fa nmemb
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is 0, the functions return 0 and the state of
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.Fa stream
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remains unchanged.
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If an error occurs, or the end-of-file is reached,
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the return value is a short object count (or zero).
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.Pp
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The function
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.Fn fread
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does not distinguish between end-of-file and error, and callers
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must use
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.Xr feof 3
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and
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.Xr ferror 3
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to determine which occurred.
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The function
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.Fn fwrite
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returns a value less than
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.Fa nmemb
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only if a write error has occurred.
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.Sh SEE ALSO
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.Xr read 2 ,
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.Xr write 2
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.Sh STANDARDS
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The functions
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.Fn fread
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and
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.Fn fwrite
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conform to
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.St -ansiC .
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