程序中，调用Bison和Flex结合的小例子（语法分析中处理数据）

 1 [root@lex total]# cat lexer.l
 2 %{
 3 
 4 #include "y.tab.h"
 5 #include <stdio.h>
 6 
 7 
 8 #undef YY_INPUT
 9 #define YY_INPUT(b,r,s) readInputForLexer(b,&r,s)
10 
11 #ifndef YYSTYPE
12 #define YYSTYPE int
13 #endif
14 extern YYSTYPE yylval;
15 
16 %}
17 
18 DIGIT   [0-9]
19 %%
20 
21 \+      { printf("got plus\n"); return FUNCTION_PLUS; }
22 \-      { printf("got minus\n"); return FUNCTION_MINUS; }
23 {DIGIT}* { printf("got number\n"); yylval = atoi(yytext); return NUMBER; }
24 \n      { printf("got end of line\n"); return EOL;}
25 %%
26 
27 
28 void yyerror(char* s) {
29     printf("error %s \n",s);
30 }
31 
32 int yywrap() {
33     return -1;
34 }
35 [root@lex total]# 

 1 [root@lex total]# cat parser.y
 2 %{
 3 #include <stdio.h>
 4 extern void yyerror(char* s);
 5 extern int yylex();
 6 extern int readInputForLexer(char* buffer,int *numBytesRead,int maxBytesToRead);
 7 %}
 8 
 9 %token FUNCTION_PLUS FUNCTION_MINUS NUMBER EOL
10 
11 %%
12 exp:
13     NUMBER FUNCTION_PLUS NUMBER { fprintf(stderr,"---\n"); }
14     |
15     NUMBER FUNCTION_MINUS NUMBER { 
16            fprintf(stderr,"left value is: %d\n",$1);
17            fprintf(stderr,"right value is: %d\n",$3);
18     }
19 ;
20 %%
21 [root@lex total]# 

 1 [root@lex total]# cat myparser.c
 2 #include <stdio.h>
 3 #include <string.h>
 4 
 5 int yyparse();
 6 int readInputForLexer( char *buffer, int *numBytesRead, int maxBytesToRead );
 7 
 8 static int globalReadOffset;
 9 // Text to read:
10 static const char *globalInputText = "23 - 5";
11 
12 int main() {
13     globalReadOffset = 0;
14     yyparse();
15     return 0;
16 }
17 
18 int readInputForLexer( char *buffer, int *numBytesRead, int maxBytesToRead ) {
19     int numBytesToRead = maxBytesToRead;
20     int bytesRemaining = strlen(globalInputText)-globalReadOffset;
21     int i;
22     if ( numBytesToRead > bytesRemaining ) { numBytesToRead = bytesRemaining; }
23     for ( i = 0; i < numBytesToRead; i++ ) {
24         buffer[i] = globalInputText[globalReadOffset+i];
25     }
26     *numBytesRead = numBytesToRead;
27     globalReadOffset += numBytesToRead;
28     return 0;
29 }
30 [root@lex total]# 

[root@lex total]# yacc -d parser.y
[root@lex total]# lex lexer.l
[root@lex total]# gcc -o myparser *.c
[root@lex total]# ./myparser
got number
got minus
got number
left value is: 23
right value is: 5
[root@lex total]#