重新定义YY_INPUT。这是一个工作示例,使用命令编译并运行
yacc -d parser.y
lex lexer.l
gcc -o myparser *.c
输入是从 globalInputText 读取的。您可以修改此示例,以便全局输入文本是您想要的任何字符串或来自您想要的任何输入源。
解析器.y:
%{
#include <stdio.h>
extern void yyerror(char* s);
extern int yylex();
extern int readInputForLexer(char* buffer,int *numBytesRead,int maxBytesToRead);
%}
%token FUNCTION_PLUS FUNCTION_MINUS NUMBER
%%
expression:
NUMBER FUNCTION_PLUS NUMBER { printf("got expression! Yay!\n"); }
;
%%
lexer.l:
%{
#include "y.tab.h"
#include <stdio.h>
#undef YY_INPUT
#define YY_INPUT(b,r,s) readInputForLexer(b,&r,s)
%}
DIGIT [0-9]
%%
\+ { printf("got plus\n"); return FUNCTION_PLUS; }
\- { printf("got minus\n"); return FUNCTION_MINUS; }
{DIGIT}* { printf("got number\n"); return NUMBER; }
%%
void yyerror(char* s) {
printf("error\n");
}
int yywrap() {
return -1;
}
myparser.c:
#include <stdio.h>
#include <string.h>
int yyparse();
int readInputForLexer( char *buffer, int *numBytesRead, int maxBytesToRead );
static int globalReadOffset;
// Text to read:
static const char *globalInputText = "3+4";
int main() {
globalReadOffset = 0;
yyparse();
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;
}