xref: /freebsd/lib/libc/stdio/funopen.3 (revision 6990ffd8a95caaba6858ad44ff1b3157d1efba8f)
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34.\"     @(#)funopen.3	8.1 (Berkeley) 6/9/93
35.\" $FreeBSD$
36.\"
37.Dd June 9, 1993
38.Dt FUNOPEN 3
39.Os
40.Sh NAME
41.Nm funopen ,
42.Nm fropen ,
43.Nm fwopen
44.Nd open a stream
45.Sh LIBRARY
46.Lb libc
47.Sh SYNOPSIS
48.Fd #include <stdio.h>
49.Ft FILE *
50.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 *)"
51.Ft FILE *
52.Fn fropen "void  *cookie" "int  (*readfn)(void *, char *, int)"
53.Ft FILE *
54.Fn fwopen "void  *cookie" "int  (*writefn)(void *, const char *, int)"
55.Sh DESCRIPTION
56The
57.Fn funopen
58function
59associates a stream with up to four
60.Dq Tn I/O No functions .
61Either
62.Fa readfn
63or
64.Fa writefn
65must be specified;
66the others can be given as an appropriately-typed
67.Dv NULL
68pointer.
69These
70.Tn I/O
71functions will be used to read, write, seek and
72close the new stream.
73.Pp
74In general, omitting a function means that any attempt to perform the
75associated operation on the resulting stream will fail.
76If the close function is omitted, closing the stream will flush
77any buffered output and then succeed.
78.Pp
79The calling conventions of
80.Fa readfn ,
81.Fa writefn ,
82.Fa seekfn
83and
84.Fa closefn
85must match those, respectively, of
86.Xr read 2 ,
87.Xr write 2 ,
88.Xr lseek 2 ,
89and
90.Xr close 2
91with the single exception that they are passed the
92.Fa cookie
93argument specified to
94.Fn funopen
95in place of the traditional file descriptor argument.
96.Pp
97Read and write
98.Tn I/O
99functions are allowed to change the underlying buffer
100on fully buffered or line buffered streams by calling
101.Xr setvbuf 3 .
102They are also not required to completely fill or empty the buffer.
103They are not, however, allowed to change streams from unbuffered to buffered
104or to change the state of the line buffering flag.
105They must also be prepared to have read or write calls occur on buffers other
106than the one most recently specified.
107.Pp
108All user
109.Tn I/O
110functions can report an error by returning \-1.
111Additionally, all of the functions should set the external variable
112.Va errno
113appropriately if an error occurs.
114.Pp
115An error on
116.Fn closefn
117does not keep the stream open.
118.Pp
119As a convenience, the include file
120.Aq Pa stdio.h
121defines the macros
122.Fn fropen
123and
124.Fn fwopen
125as calls to
126.Fn funopen
127with only a read or write function specified.
128.Sh RETURN VALUES
129Upon successful completion,
130.Fn funopen
131returns a
132.Dv FILE
133pointer.
134Otherwise,
135.Dv NULL
136is returned and the global variable
137.Va errno
138is set to indicate the error.
139.Sh ERRORS
140.Bl -tag -width Er
141.It Bq Er EINVAL
142The
143.Fn funopen
144function
145was called without either a read or write function.
146The
147.Fn funopen
148function
149may also fail and set
150.Va errno
151for any of the errors
152specified for the routine
153.Xr malloc 3 .
154.El
155.Sh SEE ALSO
156.Xr fcntl 2 ,
157.Xr open 2 ,
158.Xr fclose 3 ,
159.Xr fopen 3 ,
160.Xr fseek 3 ,
161.Xr setbuf 3
162.Sh HISTORY
163The
164.Fn funopen
165functions first appeared in
166.Bx 4.4 .
167.Sh BUGS
168The
169.Fn funopen
170function
171may not be portable to systems other than
172.Bx .
173