1 /* Fmemopen implementation.
2 Copyright (C) 2000, 2002 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Hanno Mueller, kontakt@hanno.de, 2000.
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, write to the Free
18 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
22 * fmemopen() - "my" version of a string stream
23 * Hanno Mueller, kontakt@hanno.de
26 * I needed fmemopen() for an application that I currently work on,
27 * but couldn't find it in libio. The following snippet of code is an
28 * attempt to implement what glibc's documentation describes.
30 * No, it isn't really tested yet. :-)
34 * I already see some potential problems:
36 * - I never used the "original" fmemopen(). I am sure that "my"
37 * fmemopen() behaves differently than the original version.
39 * - The documentation doesn't say wether a string stream allows
40 * seeks. I checked the old fmemopen implementation in glibc's stdio
41 * directory, wasn't quite able to see what is going on in that
42 * source, but as far as I understand there was no seek there. For
43 * my application, I needed fseek() and ftell(), so it's here.
45 * - "append" mode and fseek(p, SEEK_END) have two different ideas
46 * about the "end" of the stream.
48 * As described in the documentation, when opening the file in
49 * "append" mode, the position pointer will be set to the first null
50 * character of the string buffer (yet the buffer may already
51 * contain more data). For fseek(), the last byte of the buffer is
52 * used as the end of the stream.
54 * - It is unclear to me what the documentation tries to say when it
55 * explains what happens when you use fmemopen with a NULL
58 * Quote: "fmemopen [then] allocates an array SIZE bytes long. This
59 * is really only useful if you are going to write things to the
60 * buffer and then read them back in again."
62 * What does that mean if the original fmemopen() did not allow
63 * seeking? How do you read what you just wrote without seeking back
64 * to the beginning of the stream?
66 * - I think there should be a second version of fmemopen() that does
67 * not add null characters for each write. (At least in my
68 * application, I am not actually using strings but binary data and
69 * so I don't need the stream to add null characters on its own.)
77 #include <sys/types.h>
81 typedef struct fmemopen_cookie_struct fmemopen_cookie_t;
82 struct fmemopen_cookie_struct
93 fmemopen_read (void *cookie, char *b, size_t s)
97 c = (fmemopen_cookie_t *) cookie;
99 if (c->pos + s > c->size)
101 if ((size_t) c->pos == c->size)
103 s = c->size - c->pos;
106 memcpy (b, &(c->buffer[c->pos]), s);
109 if ((size_t) c->pos > c->maxpos)
117 fmemopen_write (void *cookie, const char *b, size_t s)
119 fmemopen_cookie_t *c;
122 c = (fmemopen_cookie_t *) cookie;
124 addnullc = s == 0 || b[s - 1] != '\0';
126 if (c->pos + s + addnullc > c->size)
128 if ((size_t) (c->pos + addnullc) == c->size)
130 __set_errno (ENOSPC);
133 s = c->size - c->pos - addnullc;
136 memcpy (&(c->buffer[c->pos]), b, s);
139 if ((size_t) c->pos > c->maxpos)
143 c->buffer[c->maxpos] = '\0';
151 fmemopen_seek (void *cookie, _IO_off64_t *p, int w)
154 fmemopen_cookie_t *c;
156 c = (fmemopen_cookie_t *) cookie;
176 if (np < 0 || (size_t) np > c->size)
186 fmemopen_close (void *cookie)
188 fmemopen_cookie_t *c;
190 c = (fmemopen_cookie_t *) cookie;
201 fmemopen (void *buf, size_t len, const char *mode)
203 cookie_io_functions_t iof;
204 fmemopen_cookie_t *c;
206 c = (fmemopen_cookie_t *) malloc (sizeof (fmemopen_cookie_t));
210 c->mybuffer = (buf == NULL);
214 c->buffer = (char *) malloc (len);
215 if (c->buffer == NULL)
230 c->maxpos = strlen (c->buffer);
237 iof.read = fmemopen_read;
238 iof.write = fmemopen_write;
239 iof.seek = fmemopen_seek;
240 iof.close = fmemopen_close;
242 return _IO_fopencookie (c, mode, iof);