程序中，调用Bison和Flex结合的小例子（类似完成语法树）

接前面的例子：程序中，调用Bison和Flex结合的小例子

要做出存储语法树结构的全局变量：

 1 [root@lex ~]# cd /soft/total

 2 [root@lex total]# ls

 3 lexer.l  lex.yy.c  myparser  myparser.c  myparser.h  parser.y  y.tab.c  y.tab.h

 4 [root@lex total]# cat myparser.h

 5 typedef struct ABlock{

 6   int left;

 7   int right;

 8 }AB;

 9 

10 typedef struct MBlock{

11   int left;

12   int right;

13 }MB;

14 

15 typedef struct Parsetree{

16   int flag; /*0 is init,1 is adding, 2 is minusing*/

17   AB adding;

18   MB minusing;

19 }Parse, *Pointer;

20 Pointer pointer;

21 [root@lex total]# 

主程序中，要完成以下几件事：

声明语法树指针(实际在上述头文件中完成)

调用词法分析/语法分析，得到语法树

根据语法树进行运算

 1 [root@lex total]# cat myparser.c

 2 #include <stdio.h>

 3 #include <string.h>

 4 #include <stdlib.h>

 5 #include "myparser.h"

 6 

 7 int yyparse();

 8 int readInputForLexer( char *buffer, int *numBytesRead, int maxBytesToRead );

 9 

10 static int globalReadOffset;

11 // Text to read:

12 static const char *globalInputText = "23 - 5";

13 

14 int main() {

15     

16     pointer=malloc(sizeof(struct Parsetree) ); 

17     pointer->flag=0;

18      

19     globalReadOffset = 0;

20     yyparse();

21 

22     //calculation

23     if (pointer->flag ==1){

24        fprintf(stderr,"addding result is: %d\n",pointer->adding.left + pointer->adding.right);

25     }

26 

27     if (pointer->flag ==2){

28        fprintf(stderr,"minusing result is: %d\n",pointer->minusing.left - pointer->minusing.right);

29     }

30     

31     free(pointer);

32     return 0;

33 }

34 

35 int readInputForLexer( char *buffer, int *numBytesRead, int maxBytesToRead ) {

36     int numBytesToRead = maxBytesToRead;

37     int bytesRemaining = strlen(globalInputText)-globalReadOffset;

38     int i;

39     if ( numBytesToRead > bytesRemaining ) { numBytesToRead = bytesRemaining; }

40     for ( i = 0; i < numBytesToRead; i++ ) {

41         buffer[i] = globalInputText[globalReadOffset+i];

42     }

43     *numBytesRead = numBytesToRead;

44     globalReadOffset += numBytesToRead;

45     return 0;

46 }

47 [root@lex total]# 

词法分析和句法分析基本不变：

 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 #include "myparser.h"

 5 extern void yyerror(char* s);

 6 extern int yylex();

 7 extern int readInputForLexer(char* buffer,int *numBytesRead,int maxBytesToRead);

 8 %}

 9 

10 

11 %token FUNCTION_PLUS FUNCTION_MINUS NUMBER EOL

12 

13 %%

14 exp:

15     NUMBER FUNCTION_PLUS NUMBER { 

16            fprintf(stderr,"---\n");

17            pointer->flag=1;

18            pointer->adding.left=$1;

19            pointer->adding.right=$3;

20     }      

21     |

22     NUMBER FUNCTION_MINUS NUMBER { 

23            fprintf(stderr,"left value is: %d\n",$1);

24            fprintf(stderr,"right value is: %d\n",$3);

25            pointer->flag=2;

26            pointer->minusing.left=$1;

27            pointer->minusing.right=$3;

28     }

29 ;

30 %%

31 [root@lex total]# 

编译和运行：

[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

minusing result is: 18

[root@lex total]#