1/********************************************************************
2 * *
3 * THIS FILE IS PART OF THE OggTheora SOFTWARE CODEC SOURCE CODE. *
4 * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS *
5 * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
6 * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING. *
7 * *
8 * THE Theora SOURCE CODE IS COPYRIGHT (C) 2002-2009 *
9 * by the Xiph.Org Foundation http://www.xiph.org/ *
10 * *
11 ********************************************************************
12
13 function:
14 last mod: $Id: theora.h,v 1.8 2004/03/15 22:17:32 derf Exp $
15
16 ********************************************************************/
17
18/**\mainpage
19 *
20 * \section intro Introduction
21 *
22 * This is the documentation for the <tt>libtheora</tt> C API.
23 *
24 * The \c libtheora package is the current reference
25 * implementation for <a href="http://www.theora.org/">Theora</a>, a free,
26 * patent-unencumbered video codec.
27 * Theora is derived from On2's VP3 codec with additional features and
28 * integration with Ogg multimedia formats by
29 * <a href="http://www.xiph.org/">the Xiph.Org Foundation</a>.
30 * Complete documentation of the format itself is available in
31 * <a href="http://www.theora.org/doc/Theora.pdf">the Theora
32 * specification</a>.
33 *
34 * \section Organization
35 *
36 * The functions documented here are divided between two
37 * separate libraries:
38 * - \c libtheoraenc contains the encoder interface,
39 * described in \ref encfuncs.
40 * - \c libtheoradec contains the decoder interface,
41 * described in \ref decfuncs, \n
42 * and additional \ref basefuncs.
43 *
44 * New code should link to \c libtheoradec. If using encoder
45 * features, it must also link to \c libtheoraenc.
46 *
47 * During initial development, prior to the 1.0 release,
48 * \c libtheora exported a different \ref oldfuncs which
49 * combined both encode and decode functions.
50 * In general, legacy API symbols can be indentified
51 * by their \c theora_ or \c OC_ namespace prefixes.
52 * The current API uses \c th_ or \c TH_ instead.
53 *
54 * While deprecated, \c libtheoraenc and \c libtheoradec
55 * together export the legacy api as well at the one documented above.
56 * Likewise, the legacy \c libtheora included with this package
57 * exports the new 1.x API. Older code and build scripts can therefore
58 * but updated independently to the current scheme.
59 */
60
61/**\file
62 * The shared <tt>libtheoradec</tt> and <tt>libtheoraenc</tt> C API.
63 * You don't need to include this directly.*/
64
65#if !defined(_O_THEORA_CODEC_H_)
66# define _O_THEORA_CODEC_H_ (1)
67# include <ogg/ogg.h>
68
69#if defined(__cplusplus)
70extern "C" {
71#endif
72
73
74
75/**\name Return codes*/
76/*@{*/
77/**An invalid pointer was provided.*/
78#define TH_EFAULT (-1)
79/**An invalid argument was provided.*/
80#define TH_EINVAL (-10)
81/**The contents of the header were incomplete, invalid, or unexpected.*/
82#define TH_EBADHEADER (-20)
83/**The header does not belong to a Theora stream.*/
84#define TH_ENOTFORMAT (-21)
85/**The bitstream version is too high.*/
86#define TH_EVERSION (-22)
87/**The specified function is not implemented.*/
88#define TH_EIMPL (-23)
89/**There were errors in the video data packet.*/
90#define TH_EBADPACKET (-24)
91/**The decoded packet represented a dropped frame.
92 The player can continue to display the current frame, as the contents of the
93 decoded frame buffer have not changed.*/
94#define TH_DUPFRAME (1)
95/*@}*/
96
97/**The currently defined color space tags.
98 * See <a href="http://www.theora.org/doc/Theora.pdf">the Theora
99 * specification</a>, Chapter 4, for exact details on the meaning
100 * of each of these color spaces.*/
101typedef enum{
102 /**The color space was not specified at the encoder.
103 It may be conveyed by an external means.*/
104 TH_CS_UNSPECIFIED,
105 /**A color space designed for NTSC content.*/
106 TH_CS_ITU_REC_470M,
107 /**A color space designed for PAL/SECAM content.*/
108 TH_CS_ITU_REC_470BG,
109 /**The total number of currently defined color spaces.*/
110 TH_CS_NSPACES
111}th_colorspace;
112
113/**The currently defined pixel format tags.
114 * See <a href="http://www.theora.org/doc/Theora.pdf">the Theora
115 * specification</a>, Section 4.4, for details on the precise sample
116 * locations.*/
117typedef enum{
118 /**Chroma decimation by 2 in both the X and Y directions (4:2:0).
119 The Cb and Cr chroma planes are half the width and half the
120 height of the luma plane.*/
121 TH_PF_420,
122 /**Currently reserved.*/
123 TH_PF_RSVD,
124 /**Chroma decimation by 2 in the X direction (4:2:2).
125 The Cb and Cr chroma planes are half the width of the luma plane, but full
126 height.*/
127 TH_PF_422,
128 /**No chroma decimation (4:4:4).
129 The Cb and Cr chroma planes are full width and full height.*/
130 TH_PF_444,
131 /**The total number of currently defined pixel formats.*/
132 TH_PF_NFORMATS
133}th_pixel_fmt;
134
135
136
137/**A buffer for a single color plane in an uncompressed image.
138 * This contains the image data in a left-to-right, top-down format.
139 * Each row of pixels is stored contiguously in memory, but successive
140 * rows need not be.
141 * Use \a stride to compute the offset of the next row.
142 * The encoder accepts both positive \a stride values (top-down in memory)
143 * and negative (bottom-up in memory).
144 * The decoder currently always generates images with positive strides.*/
145typedef struct{
146 /**The width of this plane.*/
147 int width;
148 /**The height of this plane.*/
149 int height;
150 /**The offset in bytes between successive rows.*/
151 int stride;
152 /**A pointer to the beginning of the first row.*/
153 unsigned char *data;
154}th_img_plane;
155
156/**A complete image buffer for an uncompressed frame.
157 * The chroma planes may be decimated by a factor of two in either
158 * direction, as indicated by th_info#pixel_fmt.
159 * The width and height of the Y' plane must be multiples of 16.
160 * They may need to be cropped for display, using the rectangle
161 * specified by th_info#pic_x, th_info#pic_y, th_info#pic_width,
162 * and th_info#pic_height.
163 * All samples are 8 bits.
164 * \note The term YUV often used to describe a colorspace is ambiguous.
165 * The exact parameters of the RGB to YUV conversion process aside, in
166 * many contexts the U and V channels actually have opposite meanings.
167 * To avoid this confusion, we are explicit: the name of the color
168 * channels are Y'CbCr, and they appear in that order, always.
169 * The prime symbol denotes that the Y channel is non-linear.
170 * Cb and Cr stand for "Chroma blue" and "Chroma red", respectively.*/
171typedef th_img_plane th_ycbcr_buffer[3];
172
173/**Theora bitstream information.
174 * This contains the basic playback parameters for a stream, and corresponds to
175 * the initial 'info' header packet.
176 * To initialize an encoder, the application fills in this structure and
177 * passes it to th_encode_alloc().
178 * A default encoding mode is chosen based on the values of the #quality and
179 * #target_bitrate fields.
180 * On decode, it is filled in by th_decode_headerin(), and then passed to
181 * th_decode_alloc().
182 *
183 * Encoded Theora frames must be a multiple of 16 in size;
184 * this is what the #frame_width and #frame_height members represent.
185 * To handle arbitrary picture sizes, a crop rectangle is specified in the
186 * #pic_x, #pic_y, #pic_width and #pic_height members.
187 *
188 * All frame buffers contain pointers to the full, padded frame.
189 * However, the current encoder <em>will not</em> reference pixels outside of
190 * the cropped picture region, and the application does not need to fill them
191 * in.
192 * The decoder <em>will</em> allocate storage for a full frame, but the
193 * application <em>should not</em> rely on the padding containing sensible
194 * data.
195 *
196 * It is also generally recommended that the offsets and sizes should still be
197 * multiples of 2 to avoid chroma sampling shifts when chroma is sub-sampled.
198 * See <a href="http://www.theora.org/doc/Theora.pdf">the Theora
199 * specification</a>, Section 4.4, for more details.
200 *
201 * Frame rate, in frames per second, is stored as a rational fraction, as is
202 * the pixel aspect ratio.
203 * Note that this refers to the aspect ratio of the individual pixels, not of
204 * the overall frame itself.
205 * The frame aspect ratio can be computed from pixel aspect ratio using the
206 * image dimensions.*/
207typedef struct{
208 /**\name Theora version
209 * Bitstream version information.*/
210 /*@{*/
211 unsigned char version_major;
212 unsigned char version_minor;
213 unsigned char version_subminor;
214 /*@}*/
215 /**The encoded frame width.
216 * This must be a multiple of 16, and less than 1048576.*/
217 ogg_uint32_t frame_width;
218 /**The encoded frame height.
219 * This must be a multiple of 16, and less than 1048576.*/
220 ogg_uint32_t frame_height;
221 /**The displayed picture width.
222 * This must be no larger than width.*/
223 ogg_uint32_t pic_width;
224 /**The displayed picture height.
225 * This must be no larger than height.*/
226 ogg_uint32_t pic_height;
227 /**The X offset of the displayed picture.
228 * This must be no larger than #frame_width-#pic_width or 255, whichever is
229 * smaller.*/
230 ogg_uint32_t pic_x;
231 /**The Y offset of the displayed picture.
232 * This must be no larger than #frame_height-#pic_height, and
233 * #frame_height-#pic_height-#pic_y must be no larger than 255.
234 * This slightly funny restriction is due to the fact that the offset is
235 * specified from the top of the image for consistency with the standard
236 * graphics left-handed coordinate system used throughout this API, while
237 * it is stored in the encoded stream as an offset from the bottom.*/
238 ogg_uint32_t pic_y;
239 /**\name Frame rate
240 * The frame rate, as a fraction.
241 * If either is 0, the frame rate is undefined.*/
242 /*@{*/
243 ogg_uint32_t fps_numerator;
244 ogg_uint32_t fps_denominator;
245 /*@}*/
246 /**\name Aspect ratio
247 * The aspect ratio of the pixels.
248 * If either value is zero, the aspect ratio is undefined.
249 * If not specified by any external means, 1:1 should be assumed.
250 * The aspect ratio of the full picture can be computed as
251 * \code
252 * aspect_numerator*pic_width/(aspect_denominator*pic_height).
253 * \endcode */
254 /*@{*/
255 ogg_uint32_t aspect_numerator;
256 ogg_uint32_t aspect_denominator;
257 /*@}*/
258 /**The color space.*/
259 th_colorspace colorspace;
260 /**The pixel format.*/
261 th_pixel_fmt pixel_fmt;
262 /**The target bit-rate in bits per second.
263 If initializing an encoder with this struct, set this field to a non-zero
264 value to activate CBR encoding by default.*/
265 int target_bitrate;
266 /**The target quality level.
267 Valid values range from 0 to 63, inclusive, with higher values giving
268 higher quality.
269 If initializing an encoder with this struct, and #target_bitrate is set
270 to zero, VBR encoding at this quality will be activated by default.*/
271 /*Currently this is set so that a qi of 0 corresponds to distortions of 24
272 times the JND, and each increase by 16 halves that value.
273 This gives us fine discrimination at low qualities, yet effective rate
274 control at high qualities.
275 The qi value 63 is special, however.
276 For this, the highest quality, we use one half of a JND for our threshold.
277 Due to the lower bounds placed on allowable quantizers in Theora, we will
278 not actually be able to achieve quality this good, but this should
279 provide as close to visually lossless quality as Theora is capable of.
280 We could lift the quantizer restrictions without breaking VP3.1
281 compatibility, but this would result in quantized coefficients that are
282 too large for the current bitstream to be able to store.
283 We'd have to redesign the token syntax to store these large coefficients,
284 which would make transcoding complex.*/
285 int quality;
286 /**The amount to shift to extract the last keyframe number from the granule
287 * position.
288 * This can be at most 31.
289 * th_info_init() will set this to a default value (currently <tt>6</tt>,
290 * which is good for streaming applications), but you can set it to 0 to
291 * make every frame a keyframe.
292 * The maximum distance between key frames is
293 * <tt>1<<#keyframe_granule_shift</tt>.
294 * The keyframe frequency can be more finely controlled with
295 * #TH_ENCCTL_SET_KEYFRAME_FREQUENCY_FORCE, which can also be adjusted
296 * during encoding (for example, to force the next frame to be a keyframe),
297 * but it cannot be set larger than the amount permitted by this field after
298 * the headers have been output.*/
299 int keyframe_granule_shift;
300}th_info;
301
302/**The comment information.
303 *
304 * This structure holds the in-stream metadata corresponding to
305 * the 'comment' header packet.
306 * The comment header is meant to be used much like someone jotting a quick
307 * note on the label of a video.
308 * It should be a short, to the point text note that can be more than a couple
309 * words, but not more than a short paragraph.
310 *
311 * The metadata is stored as a series of (tag, value) pairs, in
312 * length-encoded string vectors.
313 * The first occurrence of the '=' character delimits the tag and value.
314 * A particular tag may occur more than once, and order is significant.
315 * The character set encoding for the strings is always UTF-8, but the tag
316 * names are limited to ASCII, and treated as case-insensitive.
317 * See <a href="http://www.theora.org/doc/Theora.pdf">the Theora
318 * specification</a>, Section 6.3.3 for details.
319 *
320 * In filling in this structure, th_decode_headerin() will null-terminate
321 * the user_comment strings for safety.
322 * However, the bitstream format itself treats them as 8-bit clean vectors,
323 * possibly containing null characters, so the length array should be
324 * treated as their authoritative length.
325 */
326typedef struct th_comment{
327 /**The array of comment string vectors.*/
328 char **user_comments;
329 /**An array of the corresponding length of each vector, in bytes.*/
330 int *comment_lengths;
331 /**The total number of comment strings.*/
332 int comments;
333 /**The null-terminated vendor string.
334 This identifies the software used to encode the stream.*/
335 char *vendor;
336}th_comment;
337
338
339
340/**A single base matrix.*/
341typedef unsigned char th_quant_base[64];
342
343/**A set of \a qi ranges.*/
344typedef struct{
345 /**The number of ranges in the set.*/
346 int nranges;
347 /**The size of each of the #nranges ranges.
348 These must sum to 63.*/
349 const int *sizes;
350 /**#nranges <tt>+1</tt> base matrices.
351 Matrices \a i and <tt>i+1</tt> form the endpoints of range \a i.*/
352 const th_quant_base *base_matrices;
353}th_quant_ranges;
354
355/**A complete set of quantization parameters.
356 The quantizer for each coefficient is calculated as:
357 \code
358 Q=MAX(MIN(qmin[qti][ci!=0],scale[ci!=0][qi]*base[qti][pli][qi][ci]/100),
359 1024).
360 \endcode
361
362 \a qti is the quantization type index: 0 for intra, 1 for inter.
363 <tt>ci!=0</tt> is 0 for the DC coefficient and 1 for AC coefficients.
364 \a qi is the quality index, ranging between 0 (low quality) and 63 (high
365 quality).
366 \a pli is the color plane index: 0 for Y', 1 for Cb, 2 for Cr.
367 \a ci is the DCT coefficient index.
368 Coefficient indices correspond to the normal 2D DCT block
369 ordering--row-major with low frequencies first--\em not zig-zag order.
370
371 Minimum quantizers are constant, and are given by:
372 \code
373 qmin[2][2]={{4,2},{8,4}}.
374 \endcode
375
376 Parameters that can be stored in the bitstream are as follows:
377 - The two scale matrices ac_scale and dc_scale.
378 \code
379 scale[2][64]={dc_scale,ac_scale}.
380 \endcode
381 - The base matrices for each \a qi, \a qti and \a pli (up to 384 in all).
382 In order to avoid storing a full 384 base matrices, only a sparse set of
383 matrices are stored, and the rest are linearly interpolated.
384 This is done as follows.
385 For each \a qti and \a pli, a series of \a n \a qi ranges is defined.
386 The size of each \a qi range can vary arbitrarily, but they must sum to
387 63.
388 Then, <tt>n+1</tt> matrices are specified, one for each endpoint of the
389 ranges.
390 For interpolation purposes, each range's endpoints are the first \a qi
391 value it contains and one past the last \a qi value it contains.
392 Fractional values are rounded to the nearest integer, with ties rounded
393 away from zero.
394
395 Base matrices are stored by reference, so if the same matrices are used
396 multiple times, they will only appear once in the bitstream.
397 The bitstream is also capable of omitting an entire set of ranges and
398 its associated matrices if they are the same as either the previous
399 set (indexed in row-major order) or if the inter set is the same as the
400 intra set.
401
402 - Loop filter limit values.
403 The same limits are used for the loop filter in all color planes, despite
404 potentially differing levels of quantization in each.
405
406 For the current encoder, <tt>scale[ci!=0][qi]</tt> must be no greater
407 than <tt>scale[ci!=0][qi-1]</tt> and <tt>base[qti][pli][qi][ci]</tt> must
408 be no greater than <tt>base[qti][pli][qi-1][ci]</tt>.
409 These two conditions ensure that the actual quantizer for a given \a qti,
410 \a pli, and \a ci does not increase as \a qi increases.
411 This is not required by the decoder.*/
412typedef struct{
413 /**The DC scaling factors.*/
414 ogg_uint16_t dc_scale[64];
415 /**The AC scaling factors.*/
416 ogg_uint16_t ac_scale[64];
417 /**The loop filter limit values.*/
418 unsigned char loop_filter_limits[64];
419 /**The \a qi ranges for each \a ci and \a pli.*/
420 th_quant_ranges qi_ranges[2][3];
421}th_quant_info;
422
423
424
425/**The number of Huffman tables used by Theora.*/
426#define TH_NHUFFMAN_TABLES (80)
427/**The number of DCT token values in each table.*/
428#define TH_NDCT_TOKENS (32)
429
430/**A Huffman code for a Theora DCT token.
431 * Each set of Huffman codes in a given table must form a complete, prefix-free
432 * code.
433 * There is no requirement that all the tokens in a table have a valid code,
434 * but the current encoder is not optimized to take advantage of this.
435 * If each of the five grouops of 16 tables does not contain at least one table
436 * with a code for every token, then the encoder may fail to encode certain
437 * frames.
438 * The complete table in the first group of 16 does not have to be in the same
439 * place as the complete table in the other groups, but the complete tables in
440 * the remaining four groups must all be in the same place.*/
441typedef struct{
442 /**The bit pattern for the code, with the LSbit of the pattern aligned in
443 * the LSbit of the word.*/
444 ogg_uint32_t pattern;
445 /**The number of bits in the code.
446 * This must be between 0 and 32, inclusive.*/
447 int nbits;
448}th_huff_code;
449
450
451
452/**\defgroup basefuncs Functions Shared by Encode and Decode*/
453/*@{*/
454/**\name Basic shared functions
455 * These functions return information about the library itself,
456 * or provide high-level information about codec state
457 * and packet type.
458 *
459 * You must link to \c libtheoradec if you use any of the
460 * functions in this section.*/
461/*@{*/
462/**Retrieves a human-readable string to identify the library vendor and
463 * version.
464 * \return the version string.*/
465extern const char *th_version_string(void);
466/**Retrieves the library version number.
467 * This is the highest bitstream version that the encoder library will produce,
468 * or that the decoder library can decode.
469 * This number is composed of a 16-bit major version, 8-bit minor version
470 * and 8 bit sub-version, composed as follows:
471 * \code
472 * (VERSION_MAJOR<<16)+(VERSION_MINOR<<8)+(VERSION_SUBMINOR)
473 * \endcode
474 * \return the version number.*/
475extern ogg_uint32_t th_version_number(void);
476/**Converts a granule position to an absolute frame index, starting at
477 * <tt>0</tt>.
478 * The granule position is interpreted in the context of a given
479 * #th_enc_ctx or #th_dec_ctx handle (either will suffice).
480 * \param _encdec A previously allocated #th_enc_ctx or #th_dec_ctx
481 * handle.
482 * \param _granpos The granule position to convert.
483 * \returns The absolute frame index corresponding to \a _granpos.
484 * \retval -1 The given granule position was invalid (i.e. negative).*/
485extern ogg_int64_t th_granule_frame(void *_encdec,ogg_int64_t _granpos);
486/**Converts a granule position to an absolute time in seconds.
487 * The granule position is interpreted in the context of a given
488 * #th_enc_ctx or #th_dec_ctx handle (either will suffice).
489 * \param _encdec A previously allocated #th_enc_ctx or #th_dec_ctx
490 * handle.
491 * \param _granpos The granule position to convert.
492 * \return The absolute time in seconds corresponding to \a _granpos.
493 * This is the "end time" for the frame, or the latest time it should
494 * be displayed.
495 * It is not the presentation time.
496 * \retval -1 The given granule position was invalid (i.e. negative).*/
497extern double th_granule_time(void *_encdec,ogg_int64_t _granpos);
498/**Determines whether a Theora packet is a header or not.
499 * This function does no verification beyond checking the packet type bit, so
500 * it should not be used for bitstream identification; use
501 * th_decode_headerin() for that.
502 * As per the Theora specification, an empty (0-byte) packet is treated as a
503 * data packet (a delta frame with no coded blocks).
504 * \param _op An <tt>ogg_packet</tt> containing encoded Theora data.
505 * \retval 1 The packet is a header packet
506 * \retval 0 The packet is a video data packet.*/
507extern int th_packet_isheader(ogg_packet *_op);
508/**Determines whether a theora packet is a key frame or not.
509 * This function does no verification beyond checking the packet type and
510 * key frame bits, so it should not be used for bitstream identification; use
511 * th_decode_headerin() for that.
512 * As per the Theora specification, an empty (0-byte) packet is treated as a
513 * delta frame (with no coded blocks).
514 * \param _op An <tt>ogg_packet</tt> containing encoded Theora data.
515 * \retval 1 The packet contains a key frame.
516 * \retval 0 The packet contains a delta frame.
517 * \retval -1 The packet is not a video data packet.*/
518extern int th_packet_iskeyframe(ogg_packet *_op);
519/*@}*/
520
521
522/**\name Functions for manipulating header data
523 * These functions manipulate the #th_info and #th_comment structures
524 * which describe video parameters and key-value metadata, respectively.
525 *
526 * You must link to \c libtheoradec if you use any of the
527 * functions in this section.*/
528/*@{*/
529/**Initializes a th_info structure.
530 * This should be called on a freshly allocated #th_info structure before
531 * attempting to use it.
532 * \param _info The #th_info struct to initialize.*/
533extern void th_info_init(th_info *_info);
534/**Clears a #th_info structure.
535 * This should be called on a #th_info structure after it is no longer
536 * needed.
537 * \param _info The #th_info struct to clear.*/
538extern void th_info_clear(th_info *_info);
539
540/**Initialize a #th_comment structure.
541 * This should be called on a freshly allocated #th_comment structure
542 * before attempting to use it.
543 * \param _tc The #th_comment struct to initialize.*/
544extern void th_comment_init(th_comment *_tc);
545/**Add a comment to an initialized #th_comment structure.
546 * \note Neither th_comment_add() nor th_comment_add_tag() support
547 * comments containing null values, although the bitstream format does
548 * support them.
549 * To add such comments you will need to manipulate the #th_comment
550 * structure directly.
551 * \param _tc The #th_comment struct to add the comment to.
552 * \param _comment Must be a null-terminated UTF-8 string containing the
553 * comment in "TAG=the value" form.*/
554extern void th_comment_add(th_comment *_tc,const char *_comment);
555/**Add a comment to an initialized #th_comment structure.
556 * \note Neither th_comment_add() nor th_comment_add_tag() support
557 * comments containing null values, although the bitstream format does
558 * support them.
559 * To add such comments you will need to manipulate the #th_comment
560 * structure directly.
561 * \param _tc The #th_comment struct to add the comment to.
562 * \param _tag A null-terminated string containing the tag associated with
563 * the comment.
564 * \param _val The corresponding value as a null-terminated string.*/
565extern void th_comment_add_tag(th_comment *_tc,const char *_tag,
566 const char *_val);
567/**Look up a comment value by its tag.
568 * \param _tc An initialized #th_comment structure.
569 * \param _tag The tag to look up.
570 * \param _count The instance of the tag.
571 * The same tag can appear multiple times, each with a distinct
572 * value, so an index is required to retrieve them all.
573 * The order in which these values appear is significant and
574 * should be preserved.
575 * Use th_comment_query_count() to get the legal range for
576 * the \a _count parameter.
577 * \return A pointer to the queried tag's value.
578 * This points directly to data in the #th_comment structure.
579 * It should not be modified or freed by the application, and
580 * modifications to the structure may invalidate the pointer.
581 * \retval NULL If no matching tag is found.*/
582extern char *th_comment_query(th_comment *_tc,const char *_tag,int _count);
583/**Look up the number of instances of a tag.
584 * Call this first when querying for a specific tag and then iterate over the
585 * number of instances with separate calls to th_comment_query() to
586 * retrieve all the values for that tag in order.
587 * \param _tc An initialized #th_comment structure.
588 * \param _tag The tag to look up.
589 * \return The number of instances of this particular tag.*/
590extern int th_comment_query_count(th_comment *_tc,const char *_tag);
591/**Clears a #th_comment structure.
592 * This should be called on a #th_comment structure after it is no longer
593 * needed.
594 * It will free all memory used by the structure members.
595 * \param _tc The #th_comment struct to clear.*/
596extern void th_comment_clear(th_comment *_tc);
597/*@}*/
598/*@}*/
599
600
601
602#if defined(__cplusplus)
603}
604#endif
605
606#endif
607