OPEN_MEMSTREAM(3) NEWLIB OPEN_MEMSTREAM(3)NAME
4.42 `open_memstream', `open_wmemstream'--open a write stream around an
arbitrary-length string
SYNOPSIS
#include <stdio.h>
FILE *open_memstream(char **restrict BUF,
size_t *restrict SIZE);
#include <wchar.h>
FILE *open_wmemstream(wchar_t **restrict BUF,
size_t *restrict SIZE);
DESCRIPTION
`open_memstream' creates a seekable, byte-oriented `FILE' stream that
wraps an arbitrary-length buffer, created as if by `malloc'. The cur‐
rent contents of *BUF are ignored; this implementation uses *SIZE as a
hint of the maximum size expected, but does not fail if the hint was
wrong. The parameters BUF and SIZE are later stored through following
any call to `fflush' or `fclose', set to the current address and usable
size of the allocated string; although after fflush, the pointer is
only valid until another stream operation that results in a write.
Behavior is undefined if the user alters either *BUF or *SIZE prior to
`fclose'.
`open_wmemstream' is like `open_memstream' just with the associated
stream being wide-oriented. The size set in SIZE in subsequent opera‐
tions is the number of wide characters.
The stream is write-only, since the user can directly read *BUF
after a flush; see `fmemopen' for a way to wrap a string with a read‐
able stream. The user is responsible for calling `free' on the final
*BUF after `fclose'.
Any time the stream is flushed, a NUL byte is written at the current
position (but is not counted in the buffer length), so that the string
is always NUL-terminated after at most *SIZE bytes (or wide characters
in case of `open_wmemstream'). However, data previously written beyond
the current stream offset is not lost, and the NUL value written during
a flush is restored to its previous value when seeking elsewhere in the
string.
RETURNS
The return value is an open FILE pointer on success. On error, `NULL'
is returned, and `errno' will be set to EINVAL if BUF or SIZE is NULL,
ENOMEM if memory could not be allocated, or EMFILE if too many streams
are already open.
PORTABILITY
POSIX.1-2008
Supporting OS subroutines required: `sbrk'.
SEE ALSOopen_memstream is part of the library. The full documentation for is
maintained as a Texinfo manual. If info and are properly installed at
your site, the command
info
will give you access to the complete manual.
NEWLIB April 2010 OPEN_MEMSTREAM(3)
