156 lines
4.6 KiB
Groff
156 lines
4.6 KiB
Groff
.\" Copyright (c) 2013 Hudson River Trading LLC
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.\" Written by: John H. Baldwin <jhb@FreeBSD.org>
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.\" All rights reserved.
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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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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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.\" $FreeBSD$
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.\"
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.Dd August 1, 2015
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.Dt OPEN_MEMSTREAM 3
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.Os
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.Sh NAME
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.Nm open_memstream ,
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.Nm open_wmemstream
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.Nd dynamic memory buffer stream open functions
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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 FILE *
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.Fn open_memstream "char **bufp" "size_t *sizep"
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.In wchar.h
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.Ft FILE *
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.Fn open_wmemstream "wchar_t **bufp" "size_t *sizep"
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.Sh DESCRIPTION
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The
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.Fn open_memstream
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and
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.Fn open_wmemstream
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functions create a write-only, seekable stream backed by a dynamically
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allocated memory buffer.
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The
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.Fn open_memstream
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function creates a byte-oriented stream,
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while the
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.Fn open_wmemstream
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function creates a wide-oriented stream.
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.Pp
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Each stream maintains a current position and size.
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Initially,
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the position and size are set to zero.
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Each write begins at the current position and advances it the number of
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successfully written bytes for
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.Fn open_memstream
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or wide characters for
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.Fn open_wmemstream .
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If a write moves the current position beyond the length of the buffer,
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the length of the buffer is extended and a null character is appended to the
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buffer.
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.Pp
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A stream's buffer always contains a null character at the end of the buffer
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that is not included in the current length.
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.Pp
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If a stream's current position is moved beyond the current length via a
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seek operation and a write is performed,
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the characters between the current length and the current position are filled
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with null characters before the write is performed.
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.Pp
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After a successful call to
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.Xr fclose 3
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or
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.Xr fflush 3 ,
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the pointer referenced by
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.Fa bufp
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will contain the start of the memory buffer and the variable referenced by
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.Fa sizep
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will contain the smaller of the current position and the current buffer length.
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.Pp
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After a successful call to
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.Xr fflush 3 ,
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the pointer referenced by
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.Fa bufp
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and the variable referenced by
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.Fa sizep
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are only valid until the next write operation or a call to
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.Xr fclose 3 .
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.Pp
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Once a stream is closed,
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the allocated buffer referenced by
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.Fa bufp
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should be released via a call to
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.Xr free 3
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when it is no longer needed.
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.Sh IMPLEMENTATION NOTES
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Internally all I/O streams are effectively byte-oriented,
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so using wide-oriented operations to write to a stream opened via
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.Fn open_wmemstream
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results in wide characters being expanded to a stream of multibyte characters
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in stdio's internal buffers.
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These multibyte characters are then converted back to wide characters when
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written into the stream.
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As a result,
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the wide-oriented streams maintain an internal multibyte character conversion
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state that is cleared on any seek opertion that changes the current position.
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This should have no effect as long as wide-oriented output operations are used
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on a wide-oriented stream.
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.Sh RETURN VALUES
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Upon successful completion,
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.Fn open_memstream
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and
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.Fn open_wmemstream
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return a
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.Tn FILE
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pointer.
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Otherwise,
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.Dv NULL
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is returned and the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EINVAL
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The
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.Fa bufp
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or
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.Fa sizep
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argument was
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.Dv NULL .
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.It Bq Er ENOMEM
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Memory for the stream or buffer could not be allocated.
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.El
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.Sh SEE ALSO
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.Xr fclose 3 ,
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.Xr fflush 3 ,
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.Xr fopen 3 ,
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.Xr free 3 ,
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.Xr fseek 3 ,
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.Xr stdio 3 ,
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.Xr sbuf 9
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.Sh STANDARDS
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The
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.Fn open_memstream
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and
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.Fn open_wmemstream
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functions conform to
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.St -p1003.1-2008 .
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