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：

[root@lex ~]# cd /soft/total
[root@lex total]# ls
lexer.l  lex.yy.c  myparser  myparser.c  myparser.h  parser.y  y.tab.c  y.tab.h
[root@lex total]# cat myparser.h
typedef struct ABlock{
  int left;
  int right;
}AB;

typedef struct MBlock{
  int left;
  int right;
}MB;

typedef struct Parsetree{
  int flag; /*0 is init,1 is adding, 2 is minusing*/
  AB adding;
  MB minusing;
}Parse, *Pointer;
Pointer pointer;
[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

[root@lex total]# cat myparser.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "myparser.h"

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

static int globalReadOffset;
// Text to read:
static const char *globalInputText = "23 - 5";

int main() {
    
    pointer=malloc(sizeof(struct Parsetree) ); 
    pointer->flag=0;
     
    globalReadOffset = 0;
    yyparse();

    //calculation
    if (pointer->flag ==1){
       fprintf(stderr,"addding result is: %d\n",pointer->adding.left + pointer->adding.right);
    }

    if (pointer->flag ==2){
       fprintf(stderr,"minusing result is: %d\n",pointer->minusing.left - pointer->minusing.right);
    }
    
    free(pointer);
    return 0;
}

int readInputForLexer( char *buffer, int *numBytesRead, int maxBytesToRead ) {
    int numBytesToRead = maxBytesToRead;
    int bytesRemaining = strlen(globalInputText)-globalReadOffset;
    int i;
    if ( numBytesToRead > bytesRemaining ) { numBytesToRead = bytesRemaining; }
    for ( i = 0; i < numBytesToRead; i++ ) {
        buffer[i] = globalInputText[globalReadOffset+i];
    }
    *numBytesRead = numBytesToRead;
    globalReadOffset += numBytesToRead;
    return 0;
}
[root@lex total]# 

词法分析和句法分析基本不变：

[root@lex total]# cat lexer.l
%{

#include "y.tab.h"
#include <stdio.h>


#undef YY_INPUT
#define YY_INPUT(b,r,s) readInputForLexer(b,&r,s)

#ifndef YYSTYPE
#define YYSTYPE int
#endif
extern YYSTYPE yylval;

%}

DIGIT   [0-9]
%%

\+      { printf("got plus\n"); return FUNCTION_PLUS; }
\-      { printf("got minus\n"); return FUNCTION_MINUS; }
{DIGIT}* { printf("got number\n"); yylval = atoi(yytext); return NUMBER; }
\n      { printf("got end of line\n"); return EOL;}
%%


void yyerror(char* s) {
    printf("error %s \n",s);
}

int yywrap() {
    return -1;
}
[root@lex total]# 

[root@lex total]# cat parser.y
%{
#include <stdio.h>
#include "myparser.h"
extern void yyerror(char* s);
extern int yylex();
extern int readInputForLexer(char* buffer,int *numBytesRead,int maxBytesToRead);
%}


%token FUNCTION_PLUS FUNCTION_MINUS NUMBER EOL

%%
exp:
    NUMBER FUNCTION_PLUS NUMBER { 
           fprintf(stderr,"---\n");
           pointer->flag=1;
           pointer->adding.left=$1;
           pointer->adding.right=$3;
    }      
    |
    NUMBER FUNCTION_MINUS NUMBER { 
           fprintf(stderr,"left value is: %d\n",$1);
           fprintf(stderr,"right value is: %d\n",$3);
           pointer->flag=2;
           pointer->minusing.left=$1;
           pointer->minusing.right=$3;
    }
;
%%
[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]#