OPEN_MEMSTREAM(3)	   Linux Programmer's Manual	     OPEN_MEMSTREAM(3)



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, respec-
       tively, 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 out-
       put  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 ini-
       tially 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 posi-
       tion  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_wmem-
       stream() 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(), | Thread safety | MT-Safe |
       |open_wmemstream	  |		  |	    |
       +------------------+---------------+---------+

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 4.10 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				  2016-03-15		     OPEN_MEMSTREAM(3)