OPEN_MEMSTREAM
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
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NAME
open_memstream, open_wmemstream - open a dynamic memory buffer stream
SYNOPSIS
#include <stdio.h>
FILE *open_memstream(char **ptr, size_t *sizeloc);
#include <wchar.h>
FILE *open_wmemstream(wchar_t **ptr, size_t *sizeloc);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
open_memstream(),
open_wmemstream():
-
- Since glibc 2.10:
-
_POSIX_C_SOURCE >= 200809L
- Before glibc 2.10:
-
_GNU_SOURCE
DESCRIPTION
The
open_memstream()
function opens a stream for writing to a memory buffer.
The function dynamically allocates the buffer,
and the buffer automatically grows as needed.
Initially, the buffer has a size of zero.
After closing the stream, the caller should
free(3)
this buffer.
The locations pointed to by
ptr
and
sizeloc
are used to report, respectively,
the current location and the size of the buffer.
The locations referred to by these pointers are updated
each time the stream is flushed
(fflush(3))
and when the stream is closed
(fclose(3)).
These values remain valid only as long as the caller
performs no further output on the stream.
If further output is performed, then the stream
must again be flushed before trying to access these values.
A null byte is maintained at the end of the buffer.
This byte is
not
included in the size value stored at
sizeloc.
The stream maintains the notion of a current position,
which is initially zero (the start of the buffer).
Each write operation implicitly adjusts the buffer position.
The stream's buffer position can be explicitly changed with
fseek(3)
or
fseeko(3).
Moving the buffer position past the end
of the data already written fills the intervening space with
null characters.
The
open_wmemstream()
is similar to
open_memstream(),
but operates on wide characters instead of bytes.
RETURN VALUE
Upon successful completion,
open_memstream()
and
open_wmemstream()
return a
FILE
pointer.
Otherwise, NULL is returned and
errno
is set to indicate the error.
VERSIONS
open_memstream()
was already available in glibc 1.0.x.
open_wmemstream()
is available since glibc 2.4.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
open_memstream(),
open_wmemstream
| Thread safety | MT-Safe
|
CONFORMING TO
POSIX.1-2008.
These functions are not specified in POSIX.1-2001,
and are not widely available on other systems.
NOTES
There is no file descriptor associated with the file stream
returned by these functions
(i.e.,
fileno(3)
will return an error if called on the returned stream).
BUGS
In glibc before version 2.7, seeking past the end of a stream created by
open_memstream()
does not enlarge the buffer; instead the
fseek(3)
call fails, returning -1.
EXAMPLE
See
fmemopen(3).
SEE ALSO
fmemopen(3),
fopen(3),
setbuf(3)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- VERSIONS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- BUGS
-
- EXAMPLE
-
- SEE ALSO
-
- COLOPHON
-
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