open_memstream, open_wmemstream - open a dynamic memory buffer stream
Standard C library (
libc,
-lc)
#include <stdio.h>
FILE *open_memstream(char **ptr, size_t *sizeloc);
#include <wchar.h>
FILE *open_wmemstream(wchar_t **ptr, size_t *sizeloc);
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 (), open_wmemstream () |
Thread safety |
MT-Safe |
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).
Before glibc 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)