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FMEMOPEN(3)                Library Functions Manual                FMEMOPEN(3)

NAME
     fmemopen - open a stream that points to a memory buffer

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <stdio.h>

     FILE *
     fmemopen(void *restrict buffer, size_t size, const char *restrict mode);

DESCRIPTION
     The fmemopen() function associates a stream with the given buffer and
     size.  The buffer can be either NULL, or must be of the given size.  If
     the buffer is NULL, a buffer of the given size will be dynamically
     allocated using malloc(3) and freed when fclose(3) is called.

     The mode argument has the same meaning as in fopen(3).

     The stream treats the buffer as it would treat a file tracking the
     current position to perform I/O operations.  For example, in the
     beginning the stream points to the beginning of the buffer, unless a was
     specified in the mode argument, and then it points to the first NUL byte.
     If a NULL buffer was specified, then the stream will always point at the
     first byte of the buffer.

     The stream also keeps track of the size of the buffer.  The size is
     initialized depending on the mode:

     r/r+  Set to the size argument.

     w/w+  Set to 0.

     a/a+  Set to the first NUL byte, or the size argument if one is not
           found.

     Read or write operations advance the buffer, but not to exceed the given
     size of the buffer.  Trying to read beyond the size of the buffer results
     in EOF returned.  NUL bytes are read normally.  Trying to write beyond
     the size of the buffer has no effect.

     When a stream open for writing is either flushed or closed, a NUL byte is
     written at the current position or at the end of the current size as kept
     internally, if there is room.

RETURN VALUES
     Upon successful completion, fmemopen() returns a FILE pointer.
     Otherwise, NULL is returned and the global variable errno is set to
     indicate the error.

ERRORS
     [EINVAL]           The size was 0; or the mode argument is invalid; or
                        the buffer argument is NULL and the mode argument does
                        not specify a +.

     The fmemopen() function may also fail and set errno for any of the errors
     specified for the routine malloc(3).

SEE ALSO
     fclose(3), fflush(3), fopen(3), malloc(3)

STANDARDS
     The fmemopen() function conforms to IEEE Std 1003.1-2008 ("POSIX.1").

HISTORY
     The fmemopen() function first appeared in NetBSD 6.0.

NetBSD 10.99                   September 5, 2015                  NetBSD 10.99