open_memstream

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,
       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.

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_wmemstream()
       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(), open_wmemstream             │ Thread safety │ MT-Safe │
       └──────────────────────────────────────────────┴───────────────┴─────────┘

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.

EXAMPLES
       See fmemopen(3).

SEE ALSO
       fmemopen(3), fopen(3), setbuf(3)

COLOPHON
       This page is part of release 5.11 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                                2021-03-22                  OPEN_MEMSTREAM(3)