137 lines
4.7 KiB
C
137 lines
4.7 KiB
C
/*
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* Copyright (c) 2012 Nicolas George
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#ifndef AVUTIL_BPRINT_H
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#define AVUTIL_BPRINT_H
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#include "attributes.h"
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/**
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* Define a structure with extra padding to a fixed size
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* This helps ensuring binary compatibility with future versions.
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*/
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#define FF_PAD_STRUCTURE(size, ...) \
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__VA_ARGS__ \
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char reserved_padding[size - sizeof(struct { __VA_ARGS__ })];
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/**
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* Buffer to print data progressively
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*
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* The string buffer grows as necessary and is always 0-terminated.
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* The content of the string is never accessed, and thus is
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* encoding-agnostic and can even hold binary data.
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*
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* Small buffers are kept in the structure itself, and thus require no
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* memory allocation at all (unless the contents of the buffer is needed
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* after the structure goes out of scope). This is almost as lightweight as
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* declaring a local "char buf[512]".
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*
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* The length of the string can go beyond the allocated size: the buffer is
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* then truncated, but the functions still keep account of the actual total
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* length.
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*
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* In other words, buf->len can be greater than buf->size and records the
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* total length of what would have been to the buffer if there had been
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* enough memory.
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*
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* Append operations do not need to be tested for failure: if a memory
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* allocation fails, data stop being appended to the buffer, but the length
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* is still updated. This situation can be tested with
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* av_bprint_is_complete().
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*
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* The size_max field determines several possible behaviours:
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*
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* size_max = -1 (= UINT_MAX) or any large value will let the buffer be
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* reallocated as necessary, with an amortized linear cost.
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*
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* size_max = 0 prevents writing anything to the buffer: only the total
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* length is computed. The write operations can then possibly be repeated in
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* a buffer with exactly the necessary size
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* (using size_init = size_max = len + 1).
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*
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* size_max = 1 is automatically replaced by the exact size available in the
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* structure itself, thus ensuring no dynamic memory allocation. The
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* internal buffer is large enough to hold a reasonable paragraph of text,
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* such as the current paragraph.
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*/
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typedef struct AVBPrint {
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FF_PAD_STRUCTURE(1024,
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char *str; /** string so far */
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unsigned len; /** length so far */
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unsigned size; /** allocated memory */
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unsigned size_max; /** maximum allocated memory */
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char reserved_internal_buffer[1];
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)
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} AVBPrint;
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/**
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* Init a print buffer.
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*
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* @param buf buffer to init
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* @param size_init initial size (including the final 0)
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* @param size_max maximum size;
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* 0 means do not write anything, just count the length;
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* 1 is replaced by the maximum value for automatic storage
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*/
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void av_bprint_init(AVBPrint *buf, unsigned size_init, unsigned size_max);
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/**
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* Convenience macros for special values for size_max.
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*/
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#define AV_BPRINT_SIZE_UNLIMITED ((unsigned)-1)
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#define AV_BPRINT_SIZE_AUTOMATIC 1
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#define AV_BPRINT_SIZE_COUNT_ONLY 0
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/**
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* Append a formated string to a print buffer.
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*/
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void av_bprintf(AVBPrint *buf, const char *fmt, ...) av_printf_format(2, 3);
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/**
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* Append char c n times to a print buffer.
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*/
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void av_bprint_chars(AVBPrint *buf, char c, unsigned n);
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/**
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* Test if the print buffer is complete (not truncated).
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*
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* It may have been truncated due to a memory allocation failure
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* or the size_max limit (compare size and size_max if necessary).
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*/
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static inline int av_bprint_is_complete(AVBPrint *buf)
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{
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return buf->len < buf->size;
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}
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/**
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* Finalize a print buffer.
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*
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* The print buffer can no longer be used afterwards,
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* but the len and size fields are still valid.
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*
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* @arg[out] ret_str if not NULL, used to return a permanent copy of the
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* buffer contents, or NULL if memory allocation fails;
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* if NULL, the buffer is discarded and freed
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* @return 0 for success or error code (probably AVERROR(ENOMEM))
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*/
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int av_bprint_finalize(AVBPrint *buf, char **ret_str);
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#endif /* AVUTIL_BPRINT_H */
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