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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | VERSIONS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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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 5.10 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 2020-06-09 OPEN_MEMSTREAM(3)
Pages that refer to this page: fmemopen(3), fopen(3), malloc_info(3)
Copyright and license for this manual page
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