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，

C/C++ code

%{/* * 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;}