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FMEMOPEN(3) NetBSD Library Functions Manual FMEMOPEN(3)
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by Kimmo Suominen.
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fmemopen -- open a stream that points to a memory buffer
Standard C Library (libc, -lc)
fmemopen(void *restrict buffer, size_t size, const char *restrict mode);
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
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.
Upon successful completion, fmemopen() returns a FILE pointer. Other-
wise, NULL is returned and the global variable errno is set to indicate
[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).
fclose(3), fflush(3), fopen(3), malloc(3)
The fmemopen() function conforms to IEEE Std 1003.1-2008 (``POSIX.1'').
The fmemopen() function first appeared in NetBSD 6.0.
NetBSD 9.99 September 5, 2015 NetBSD 9.99