fmemopen(3) - NetBSD Manual Pages

FMEMOPEN(3)             NetBSD 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 allo-
     cated 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 cur-
     rent 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 ini-
     tialized 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.  Other-
     wise, 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 9.3                     September 5, 2015                    NetBSD 9.3