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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | EXAMPLE | SEE ALSO | COLOPHON |
OPEN_MEMSTREAM(3) Linux Programmer's Manual OPEN_MEMSTREAM(3)
open_memstream, open_wmemstream - open a dynamic memory buffer
stream
#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
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.
Upon successful completion, open_memstream() and open_wmemstream()
return a FILE pointer. Otherwise, NULL is returned and errno is set
to indicate the error.
open_memstream() was already available in glibc 1.0.x.
open_wmemstream() is available since glibc 2.4.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────┼───────────────┼─────────┤
│open_memstream(), │ Thread safety │ MT-Safe │
│open_wmemstream │ │ │
└──────────────────┴───────────────┴─────────┘
POSIX.1-2008. These functions are not specified in POSIX.1-2001, and
are not widely available on other systems.
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).
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.
See fmemopen(3).
fmemopen(3), fopen(3), setbuf(3)
This page is part of release 4.12 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/.
GNU 2016-03-15 OPEN_MEMSTREAM(3)
Pages that refer to this page: fmemopen(3), fopen(3), malloc_info(3)