compat/vsnprintf: return number of bytes required on truncation.
[libav.git] / compat / msvcrt / snprintf.c
1 /*
2 * C99-compatible snprintf() and vsnprintf() implementations
3 * Copyright (c) 2012 Ronald S. Bultje <rsbultje@gmail.com>
4 *
5 * This file is part of Libav.
6 *
7 * Libav is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
11 *
12 * Libav is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
16 *
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with Libav; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20 */
21
22 #include <stdio.h>
23 #include <stdarg.h>
24 #include <limits.h>
25 #include <string.h>
26
27 #include "libavutil/error.h"
28
29 #if !defined(va_copy) && defined(_MSC_VER)
30 #define va_copy(dst, src) ((dst) = (src))
31 #endif
32
33 int avpriv_snprintf(char *s, size_t n, const char *fmt, ...)
34 {
35 va_list ap;
36 int ret;
37
38 va_start(ap, fmt);
39 ret = avpriv_vsnprintf(s, n, fmt, ap);
40 va_end(ap);
41
42 return ret;
43 }
44
45 int avpriv_vsnprintf(char *s, size_t n, const char *fmt,
46 va_list ap)
47 {
48 int ret;
49 va_list ap_copy;
50
51 if (n == 0)
52 return _vscprintf(fmt, ap);
53 else if (n > INT_MAX)
54 return AVERROR(EOVERFLOW);
55
56 /* we use n - 1 here because if the buffer is not big enough, the MS
57 * runtime libraries don't add a terminating zero at the end. MSDN
58 * recommends to provide _snprintf/_vsnprintf() a buffer size that
59 * is one less than the actual buffer, and zero it before calling
60 * _snprintf/_vsnprintf() to workaround this problem.
61 * See http://msdn.microsoft.com/en-us/library/1kt27hek(v=vs.80).aspx */
62 memset(s, 0, n);
63 va_copy(ap_copy, ap);
64 ret = _vsnprintf(s, n - 1, fmt, ap_copy);
65 va_end(ap_copy);
66 if (ret == -1)
67 ret = _vscprintf(fmt, ap);
68
69 return ret;
70 }