Question

我正在尝试为类似Pascal的迷你语言编写一个编译器。我正在使用Flex和Bison，我想出了这个错误。

我的Flex文件：

%{
#include "y.tab.h"
#include <stdlib.h>
#include <string.h>
#include <math.h>
void yyerror(char *);
%}

%%

[1-9][0-9]*     {
                yylval.i = atoi(yytext);
                return INT;
}

program     return PROGRAM;
or          return OR;
and         return AND;
not         return NOT;
if          return IF;
else        return ELSE ;
while       return WHILE;
"+"         return PLUS;
"-"         return MINUS;
"*"         return MUL;
"/"         return DIV;
"["         return LSB;
"]"         return RSB;
"{"         return LCB;
"}"         return RCB;
"("         return LEFTPAR;
")"         return RIGHTPAR;
":="        return ASSIGN;
"=="        return ISEQUAL;
"<"         return LTHAN;
">"         return GTHAN;
"<>"        return NOTEQUAL;
"<="        return LESSEQUAL;
">="        return GREATEREQUAL;

[a-zA-z][a-z0-9]*   {
                    yylval.s = (char*)malloc(strlen(yytext)*sizeof(char));
                    strcopy(yylval.s,yytext);
                    return ID;
}               

[ \t\n]+                            /* eat up whitespace */         

.                                   yyerror("Unknown Character");

%%
int yywrap(void) {
    return 1;
}

我的野牛档案：

%{
    #include <stdio.h>
    #include <string.h>
    int yylex(void);
    void yyerror(char *s);
%}

%union {
    int i;
    char *s;
};

%token <i> INTEGERNUM

%token PROGRAM;
%token OR;
%token AND;
%token NOT;
%token IF;
%token ELSE;
%token WHILE;
%token PLUS;
%token MINUS;
%token MUL;
%token DIV;
%token LSB;
%token RSB;
%token LCB;
%token RCB;
%token LEFTPAR;
%token RIGHTPAR;
%token ID;
%token INT;
%token ASSIGN;
%token ISEQUAL;
%token LTHAN;
%token GTHAN;
%token NOTEQUAL;
%token LESSEQUAL;
%token GREATEREQUAL;

%%

program:
        PROGRAM ID block
        ;

block:
        LCB sequence RCB
        ;

sequence:
        statement ';' sequence
        | statement ';' 
        ;

bracketsSeq:
        LCB sequence RCB
        ;

brackOrStat:        
        bracketsSeq
        | statement
        ;

statement:
        assignmentStat
        |ifStat
        |whileStat
        |
        ;

assignmentStat:
        ID ':=' expression

ifStat:
        IF LEFTPAR condition RIGHTPAR brackOrStat elsepart
        ;

elsepart:
        ELSE brackOrStat
        |
        ;

whileStat:
        WHILE LEFTPAR condition RIGHTPAR brackOrStat
        ;

expression:
        optionalSign expression
        |expression addOper expression
        |term
        ;

term:
        term mulOper term
        |factor
        ;

factor:
        INT
        |LEFTPAR expression RIGHTPAR
        |ID
        ;

condition:
        condition AND condition
        |boolterm
        ;

boolterm:
        boolterm OR boolterm
        |boolfactor
        ;

boolfactor:
        NOT LSB condition RSB
        |LSB condition RSB
        |expression relationalOper expression
        ;

relationalOper:
        ISEQUAL
        |LTHAN
        |GTHAN
        |NOTEQUAL
        |LESSEQUAL
        |GREATEREQUAL
        ;

addOper:
        PLUS
        |MINUS
        ;

mulOper:
        MUL
        |DIV
        ;

optionalSign:
        addOper
        |
        ;

%%

int main( int argc, char **argv )
             {
             printf("TEST\n");

             }

我执行的一系列步骤是：

$ ./bison.exe -dy comp.y
$ ./flex.exe comp.l
$ gcc -c -w lex.yy.c 
$ gcc -c -w comp.tab.c
$ gcc comp.tab.o lex.yy.o -o ex
comp.tab.o:comp.tab.c:(.text+0x4cd): undefined reference to `_yyerror'
comp.tab.o:comp.tab.c:(.text+0x61c): undefined reference to `_yyerror'
lex.yy.o:lex.yy.c:(.text+0x34a): undefined reference to `_strcopy'
lex.yy.o:lex.yy.c:(.text+0x362): undefined reference to `_yyerror'
/usr/lib/gcc/i686-pc-cygwin/3.4.4/../../../../i686-pc-cygwin/bin/ld: lex.yy.o: bad reloc address                0x828 in section `.rdata'
/usr/lib/gcc/i686-pc-cygwin/3.4.4/../../../../i686-pc-cygwin/bin/ld: final link failed: Invalid                operation
collect2: ld returned 1 exit status
$

关于宣告什么以及原因似乎存在的任何建议我已经宣布了错误的方式！

Answer 1

宣布yyerror是不够的。您必须提供定义。

bison manual建议将以下内容作为最小实现：

 void yyerror (char const *s) {
   fprintf (stderr, "%s\n", s);
 }

您遇到的另一个问题是您在flex文件中拼错了strcpy。

更准确地说，链接器错误显示的另一个问题是拼写错误的strcpy，因为您的复制代码不正确。它不考虑必须终止字符串的NUL字节。 strcpy将复制该字节，结果是它将在未分配的存储中写入0。你会发现使用strdup要简单得多。（当你完成它们时，不要忘记你需要free字符串。）

使用Flex和Bison进行编译时未定义的对“_yyerror”的引用

1 个答案: