.\" Copyright (c) 1990, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" This code is derived from software contributed to Berkeley by .\" Chris Torek. .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)funopen.3 8.1 (Berkeley) 6/9/93 .\" $FreeBSD: src/lib/libc/stdio/funopen.3,v 1.12 2001/10/01 16:08:59 ru Exp $ .\" .Dd June 9, 1993 .Dt FUNOPEN 3 .Os .Sh NAME .Nm funopen , .Nm fropen , .Nm fwopen .Nd open a stream .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In stdio.h .Ft FILE * .Fn funopen "const void *cookie" "int (*readfn)(void *, char *, int)" "int (*writefn)(void *, const char *, int)" "fpos_t (*seekfn)(void *, fpos_t, int)" "int (*closefn)(void *)" .Ft FILE * .Fn fropen "void *cookie" "int (*readfn)(void *, char *, int)" .Ft FILE * .Fn fwopen "void *cookie" "int (*writefn)(void *, const char *, int)" .Sh DESCRIPTION The .Fn funopen function associates a stream with up to four .Dq Tn I/O No functions . Either .Fa readfn or .Fa writefn must be specified; the others can be given as an appropriately-typed .Dv NULL pointer. These .Tn I/O functions will be used to read, write, seek and close the new stream. .Pp In general, omitting a function means that any attempt to perform the associated operation on the resulting stream will fail. If the close function is omitted, closing the stream will flush any buffered output and then succeed. .Pp The calling conventions of .Fa readfn , .Fa writefn , .Fa seekfn and .Fa closefn must match those, respectively, of .Xr read 2 , .Xr write 2 , .Xr lseek 2 , and .Xr close 2 with the single exception that they are passed the .Fa cookie argument specified to .Fn funopen in place of the traditional file descriptor argument. .Pp Read and write .Tn I/O functions are allowed to change the underlying buffer on fully buffered or line buffered streams by calling .Xr setvbuf 3 . 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. .Pp All user .Tn I/O functions can report an error by returning \-1. Additionally, all of the functions should set the external variable .Va errno appropriately if an error occurs. .Pp An error on .Fn closefn does not keep the stream open. .Pp As a convenience, the include file .Aq Pa stdio.h defines the macros .Fn fropen and .Fn fwopen as calls to .Fn funopen with only a read or write function specified. .Sh RETURN VALUES Upon successful completion, .Fn funopen returns a .Dv FILE pointer. Otherwise, .Dv NULL is returned and the global variable .Va errno is set to indicate the error. .Sh ERRORS .Bl -tag -width Er .It Bq Er EINVAL The .Fn funopen function was called without either a read or write function. The .Fn funopen function may also fail and set .Va errno for any of the errors specified for the routine .Xr malloc 3 . .El .Sh SEE ALSO .Xr fcntl 2 , .Xr open 2 , .Xr fclose 3 , .Xr fopen 3 , .Xr fseek 3 , .Xr setbuf 3 .Sh HISTORY The .Fn funopen functions first appeared in .Bx 4.4 . .Sh BUGS The .Fn funopen function may not be portable to systems other than .Bx .