bprint.h (5997B)
1 /* 2 * Copyright (c) 2012 Nicolas George 3 * 4 * This file is part of FFmpeg. 5 * 6 * FFmpeg 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. 10 * 11 * FFmpeg 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. 15 * 16 * You should have received a copy of the GNU Lesser General Public 17 * License along with FFmpeg; if not, write to the Free Software 18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 19 */ 20 21 #ifndef AVUTIL_BPRINT_H 22 #define AVUTIL_BPRINT_H 23 24 #include "attributes.h" 25 26 /** 27 * Define a structure with extra padding to a fixed size 28 * This helps ensuring binary compatibility with future versions. 29 */ 30 #define FF_PAD_STRUCTURE(size, ...) \ 31 __VA_ARGS__ \ 32 char reserved_padding[size - sizeof(struct { __VA_ARGS__ })]; 33 34 /** 35 * Buffer to print data progressively 36 * 37 * The string buffer grows as necessary and is always 0-terminated. 38 * The content of the string is never accessed, and thus is 39 * encoding-agnostic and can even hold binary data. 40 * 41 * Small buffers are kept in the structure itself, and thus require no 42 * memory allocation at all (unless the contents of the buffer is needed 43 * after the structure goes out of scope). This is almost as lightweight as 44 * declaring a local "char buf[512]". 45 * 46 * The length of the string can go beyond the allocated size: the buffer is 47 * then truncated, but the functions still keep account of the actual total 48 * length. 49 * 50 * In other words, buf->len can be greater than buf->size and records the 51 * total length of what would have been to the buffer if there had been 52 * enough memory. 53 * 54 * Append operations do not need to be tested for failure: if a memory 55 * allocation fails, data stop being appended to the buffer, but the length 56 * is still updated. This situation can be tested with 57 * av_bprint_is_complete(). 58 * 59 * The size_max field determines several possible behaviours: 60 * 61 * size_max = -1 (= UINT_MAX) or any large value will let the buffer be 62 * reallocated as necessary, with an amortized linear cost. 63 * 64 * size_max = 0 prevents writing anything to the buffer: only the total 65 * length is computed. The write operations can then possibly be repeated in 66 * a buffer with exactly the necessary size 67 * (using size_init = size_max = len + 1). 68 * 69 * size_max = 1 is automatically replaced by the exact size available in the 70 * structure itself, thus ensuring no dynamic memory allocation. The 71 * internal buffer is large enough to hold a reasonable paragraph of text, 72 * such as the current paragraph. 73 */ 74 typedef struct AVBPrint { 75 FF_PAD_STRUCTURE(1024, 76 char *str; /** string so far */ 77 unsigned len; /** length so far */ 78 unsigned size; /** allocated memory */ 79 unsigned size_max; /** maximum allocated memory */ 80 char reserved_internal_buffer[1]; 81 ) 82 } AVBPrint; 83 84 /** 85 * Convenience macros for special values for av_bprint_init() size_max 86 * parameter. 87 */ 88 #define AV_BPRINT_SIZE_UNLIMITED ((unsigned)-1) 89 #define AV_BPRINT_SIZE_AUTOMATIC 1 90 #define AV_BPRINT_SIZE_COUNT_ONLY 0 91 92 /** 93 * Init a print buffer. 94 * 95 * @param buf buffer to init 96 * @param size_init initial size (including the final 0) 97 * @param size_max maximum size; 98 * 0 means do not write anything, just count the length; 99 * 1 is replaced by the maximum value for automatic storage; 100 * any large value means that the internal buffer will be 101 * reallocated as needed up to that limit; -1 is converted to 102 * UINT_MAX, the largest limit possible. 103 * Check also AV_BPRINT_SIZE_* macros. 104 */ 105 void av_bprint_init(AVBPrint *buf, unsigned size_init, unsigned size_max); 106 107 /** 108 * Init a print buffer using a pre-existing buffer. 109 * 110 * The buffer will not be reallocated. 111 * 112 * @param buf buffer structure to init 113 * @param buffer byte buffer to use for the string data 114 * @param size size of buffer 115 */ 116 void av_bprint_init_for_buffer(AVBPrint *buf, char *buffer, unsigned size); 117 118 /** 119 * Append a formated string to a print buffer. 120 */ 121 void av_bprintf(AVBPrint *buf, const char *fmt, ...) av_printf_format(2, 3); 122 123 /** 124 * Append char c n times to a print buffer. 125 */ 126 void av_bprint_chars(AVBPrint *buf, char c, unsigned n); 127 128 /** 129 * Allocate bytes in the buffer for external use. 130 * 131 * @param[in] buf buffer structure 132 * @param[in] size required size 133 * @param[out] mem pointer to the memory area 134 * @param[out] actual_size size of the memory area after allocation; 135 * can be larger or smaller than size 136 */ 137 void av_bprint_get_buffer(AVBPrint *buf, unsigned size, 138 unsigned char **mem, unsigned *actual_size); 139 140 /** 141 * Reset the string to "" but keep internal allocated data. 142 */ 143 void av_bprint_clear(AVBPrint *buf); 144 145 /** 146 * Test if the print buffer is complete (not truncated). 147 * 148 * It may have been truncated due to a memory allocation failure 149 * or the size_max limit (compare size and size_max if necessary). 150 */ 151 static inline int av_bprint_is_complete(AVBPrint *buf) 152 { 153 return buf->len < buf->size; 154 } 155 156 /** 157 * Finalize a print buffer. 158 * 159 * The print buffer can no longer be used afterwards, 160 * but the len and size fields are still valid. 161 * 162 * @arg[out] ret_str if not NULL, used to return a permanent copy of the 163 * buffer contents, or NULL if memory allocation fails; 164 * if NULL, the buffer is discarded and freed 165 * @return 0 for success or error code (probably AVERROR(ENOMEM)) 166 */ 167 int av_bprint_finalize(AVBPrint *buf, char **ret_str); 168 169 #endif /* AVUTIL_BPRINT_H */