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:

       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 ex-
       plicitly 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.

       Upon  successful completion, open_memstream() and open_wmemstream() re-
       turn 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_wmem-
       stream() is available since glibc 2.4.

       For an  explanation  of  the  terms  used  in  this  section,  see  at-

       |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)

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GNU                               2017-09-15                 OPEN_MEMSTREAM(3)
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