请大仙们帮我看看这是什么代码呀，这是我从libcue里面拿出来的，神奇的VC竟然可以编译
下面的代码是从cue_parser.y这个文件里面拿出来的，搞不懂，
%{/* * Copyright (c) 2004, 2005, 2006, 2007, Svend Sorensen * Copyright (c) 2009, 2010 Jochen Keil * For license terms, see the file COPYING in this distribution. */#include <stdlib.h>#include <stdio.h>#include <string.h>#include "config.h"#include "cd.h"#include "time.h"#ifdef YY_BUF_SIZE#undef YY_BUF_SIZE#endif#define YY_BUF_SIZE 16384#define YYDEBUG 1char fnamebuf[PARSER_BUFFER];/* debugging *///int yydebug = 1;extern int yylineno;extern FILE* yyin;static Cd *cd = NULL;static Track *track = NULL;static Track *prev_track = NULL;static Cdtext *cdtext = NULL;static Rem *rem = NULL;static char *prev_filename = NULL; /* last file in or before last track */static char *cur_filename = NULL; /* last file in the last track */static char *new_filename = NULL; /* last file in this track *//* lexer interface */typedef struct yy_buffer_state* YY_BUFFER_STATE;int yylex(void);void yyerror(const char*);YY_BUFFER_STATE yy_scan_string(const char*);YY_BUFFER_STATE yy_create_buffer(FILE*, int);void yy_switch_to_buffer(YY_BUFFER_STATE);void yy_delete_buffer(YY_BUFFER_STATE);/* parser interface */int yyparse(void);Cd *cue_parse_file(FILE *fp);Cd *cue_parse_string(const char*);%}%start cuefile%union { long ival; char *sval;}%token <ival> NUMBER%token <sval> STRING/* global (header) */%token CATALOG%token CDTEXTFILE%token FFILE%token BINARY%token MOTOROLA%token AIFF%token WAVE%token MP3/* track */%token TRACK%token <ival> AUDIO%token <ival> MODE1_2048%token <ival> MODE1_2352%token <ival> MODE2_2336%token <ival> MODE2_2048%token <ival> MODE2_2342%token <ival> MODE2_2332%token <ival> MODE2_2352/* ISRC is with CD_TEXT */%token TRACK_ISRC%token FLAGS%token <ival> PRE%token <ival> DCP%token <ival> FOUR_CH%token <ival> SCMS%token PREGAP%token INDEX%token POSTGAP/* CD-TEXT */%token <ival> TITLE%token <ival> PERFORMER%token <ival> SONGWRITER%token <ival> COMPOSER%token <ival> ARRANGER%token <ival> MESSAGE%token <ival> DISC_ID%token <ival> GENRE%token <ival> TOC_INFO1%token <ival> TOC_INFO2%token <ival> UPC_EAN%token <ival> ISRC%token <ival> SIZE_INFO%type <ival> track_mode%type <ival> track_flag%type <ival> time%type <ival> cdtext_item/* REM */%type <ival> rem_item%token <ival> DATE%token <ival> REPLAYGAIN_ALBUM_GAIN%token <ival> REPLAYGAIN_ALBUM_PEAK%token <ival> REPLAYGAIN_TRACK_GAIN%token <ival> REPLAYGAIN_TRACK_PEAK%%cuefile : new_cd global_statements track_list ;new_cd : /* empty */ { cd = cd_init(); cdtext = cd_get_cdtext(cd); rem = cd_get_rem(cd); } ;global_statements : /* empty */ | global_statements global_statement ;global_statement : CATALOG STRING '\n' { cd_set_catalog(cd, $2); } | CDTEXTFILE STRING '\n' { cd_set_cdtextfile(cd, $2); } | cdtext | rem | track_data | error '\n' ;track_data : FFILE STRING file_format '\n' { if (NULL != new_filename) { yyerror("too many files specified\n"); } new_filename = strncpy(fnamebuf, $2, sizeof(fnamebuf)); new_filename[strlen(new_filename)] = '\0'; } ;track_list : track | track_list track ;track : new_track track_def track_statements ;file_format : BINARY | MOTOROLA | AIFF | WAVE | MP3 ;new_track : /*empty */ { /* save previous track, to later set length */ prev_track = track; track = cd_add_track(cd); cdtext = track_get_cdtext(track); rem = track_get_rem(track); cur_filename = new_filename; if (NULL != cur_filename) prev_filename = cur_filename; if (NULL == prev_filename) yyerror("no file specified for track"); else track_set_filename(track, prev_filename); new_filename = NULL; } ;track_def : TRACK NUMBER track_mode '\n' { track_set_mode(track, $3); } ;track_mode : AUDIO | MODE1_2048 | MODE1_2352 | MODE2_2336 | MODE2_2048 | MODE2_2342 | MODE2_2332 | MODE2_2352 ;track_statements : track_statement | track_statements track_statement ;track_statement : cdtext | rem | FLAGS track_flags '\n' | TRACK_ISRC STRING '\n' { track_set_isrc(track, $2); } | PREGAP time '\n' { track_set_zero_pre(track, $2); } | INDEX NUMBER time '\n' { int i = track_get_nindex(track); long prev_length; if (0 == i) { /* first index */ track_set_start(track, $3); if (NULL != prev_track && NULL == cur_filename) { /* track shares file with previous track */ prev_length = $3 - track_get_start(prev_track); track_set_length(prev_track, prev_length); } } for (; i <= $2; i++) track_add_index(track, \ track_get_zero_pre(track) + $3 \ - track_get_start(track)); } | POSTGAP time '\n' { track_set_zero_post(track, $2); } | track_data | error '\n' ;track_flags : /* empty */ | track_flags track_flag { track_set_flag(track, $2); } ;track_flag : PRE | DCP | FOUR_CH | SCMS ;cdtext : cdtext_item STRING '\n' { cdtext_set ($1, $2, cdtext); } ;cdtext_item : TITLE | PERFORMER | SONGWRITER | COMPOSER | ARRANGER | MESSAGE | DISC_ID | GENRE | TOC_INFO1 | TOC_INFO2 | UPC_EAN | ISRC | SIZE_INFO ;time : NUMBER | NUMBER ':' NUMBER ':' NUMBER { $$ = time_msf_to_frame($1, $3, $5); } ;rem : rem_item STRING '\n' { rem_set($1, $2, rem); } ;rem_item : DATE | REPLAYGAIN_ALBUM_GAIN | REPLAYGAIN_ALBUM_PEAK | REPLAYGAIN_TRACK_GAIN | REPLAYGAIN_TRACK_PEAK ;%%/* lexer interface */void yyerror (const char *s){ fprintf(stderr, "%d: %s\n", yylineno, s);}Cd *cue_parse_file(FILE *fp){ YY_BUFFER_STATE buffer = NULL; yyin = fp; buffer = yy_create_buffer(yyin, YY_BUF_SIZE); yy_switch_to_buffer(buffer); if (0 == yyparse()) { yy_delete_buffer(buffer); return cd; } yy_delete_buffer(buffer); return NULL;}Cd *cue_parse_string(const char* string){ YY_BUFFER_STATE buffer = NULL; buffer = yy_scan_string(string); if (0 == yyparse()) { yy_delete_buffer(buffer); return cd; } yy_delete_buffer(buffer); if(cd) cd_delete(cd); return NULL;}