FUNOPEN(3) NEWLIB FUNOPEN(3)NAME
4.29 `funopen', `fropen', `fwopen'--open a stream with custom callbacks
SYNOPSIS
#include <stdio.h>
FILE *funopen(const void *COOKIE,
int (*READFN) (void *cookie, char *buf, int n),
int (*WRITEFN) (void *cookie, const char *buf, int n),
fpos_t (*SEEKFN) (void *cookie, fpos_t off, int whence),
int (*CLOSEFN) (void *cookie));
FILE *fropen(const void *COOKIE,
int (*READFN) (void *cookie, char *buf, int n));
FILE *fwopen(const void *COOKIE,
int (*WRITEFN) (void *cookie, const char *buf, int n));
DESCRIPTION
`funopen' creates a `FILE' stream where I/O is performed using custom
callbacks. At least one of READFN and WRITEFN must be provided, which
determines whether the stream behaves with mode <"r">, <"w">, or
<"r+">.
READFN should return -1 on failure, or else the number of bytes read
(0 on EOF). It is similar to `read', except that <int> rather than
<size_t> bounds a transaction size, and COOKIE will be passed as the
first argument. A NULL READFN makes attempts to read the stream fail.
WRITEFN should return -1 on failure, or else the number of bytes
written. It is similar to `write', except that <int> rather than
<size_t> bounds a transaction size, and COOKIE will be passed as the
first argument. A NULL WRITEFN makes attempts to write the stream
fail.
SEEKFN should return (fpos_t)-1 on failure, or else the current file
position. It is similar to `lseek', except that COOKIE will be passed
as the first argument. A NULL SEEKFN makes the stream behave similarly
to a pipe in relation to stdio functions that require positioning.
This implementation assumes fpos_t and off_t are the same type.
CLOSEFN should return -1 on failure, or 0 on success. It is similar
to `close', except that COOKIE will be passed as the first argument. A
NULL CLOSEFN merely flushes all data then lets `fclose' succeed. A
failed close will still invalidate the stream.
Read and write I/O functions are allowed to change the underlying
buffer on fully buffered or line buffered streams by calling `setvbuf'.
They are also not required to completely fill or empty the buffer.
They are not, however, allowed to change streams from unbuffered to
buffered or to change the state of the line buffering flag. They must
also be prepared to have read or write calls occur on buffers other
than the one most recently specified.
The functions `fropen' and `fwopen' are convenience macros around
`funopen' that only use the specified callback.
RETURNS
The return value is an open FILE pointer on success. On error, `NULL'
is returned, and `errno' will be set to EINVAL if a function pointer is
missing, ENOMEM if the stream cannot be created, or EMFILE if too many
streams are already open.
PORTABILITY
This function is a newlib extension, copying the prototype from BSD.
It is not portable. See also the `fopencookie' interface from Linux.
Supporting OS subroutines required: `sbrk'.
SEE ALSOfunopen is part of the library. The full documentation for is main‐
tained as a Texinfo manual. If info and are properly installed at your
site, the command
info
will give you access to the complete manual.
NEWLIB April 2010 FUNOPEN(3)
