使用 flex 和 bison 解析文件时出现语法错误

Question

我正在解析以下文件：

BEGIN BLOCK BLK_ROWDEC            
        NAME                          cell_rowdec
        SIZE                          UNI_rowdecSize
        ITERATE                       itr_rows
        DIRECTION                     lgDir_rowdec
        STRAP                         STRD1,STRD3,STRD2
        WRAP                          WRD1
        VIA                           VIAB,VIAC,VIAD
ENDS BLK_ROWDEC

我的flex和bison文件如下：

lexa.l

%{
#include <iostream>
#include <stdio.h>
const char s[2] = " ";
#include "yacc.tab.h"
char *token;
#define YY_DECL extern "C" int yylex()
int line_num = 1;



using namespace std;
%}

DOT             "."
COLON           ":"
SEMICOLON       ";"
COMMA           ","
ANGLE_LEFT      "<"
ANGLE_RIGHT     ">"
AT              "@"
EQUAL           "="
SQUARE_OPEN     "["
SQUARE_CLOSE    [^\]"]"
OPENBRACE       "\("
CLOSEBRACE      "\)"
QUOTE           "\""
QUOTE_OPEN      "\""
QUOTE_CLOSE     [^\]"\""
SPACE           " "
TAB             "\t"
CRLF            "\r\n"
QUOTED_PAIR     "\"[^\r\n]
DIGIT           [0-9]
ALPHA           [a-zA-Z]
QTEXT           [0-9a-zA-Z!#$%&'()*+,\-.\/:;<=>?@\[\]^_`{|}~]


%%



[ \t]         ;


^BEGIN(.*)\r?\n+\s*BEGIN(.*)     {   printf("\nError : two continous BEGIN is not allowed : "); }

^ENDS(.*)\r?\n+\s*ENDS(.*)   {   printf("\nError : two continous END is not allowed : \n"); }




NAME          {  yylval.sval = strdup(yytext);
    return TOK_NAME; }

SIZE          { yylval.sval = strdup(yytext);
      return TOK_SIZE; }

ITERATE       { yylval.sval = strdup(yytext);
       return TOK_ITERATE; }

DIRECTION   { yylval.sval = strdup(yytext);
      return TOK_DIRECTION; }

STRAP       { yylval.sval = strdup(yytext);
      return TOK_STRAP; }

WRAP        { yylval.sval = strdup(yytext);
      return TOK_WRAP; }

VIA     { yylval.sval = strdup(yytext);
      return TOK_VIA; }

ENDS        { yylval.sval = strdup(yytext);
      return TOK_END; }

BEGIN       { yylval.sval = strdup(yytext);
      return TOK_BEGIN; }

BLOCK       { yylval.sval = strdup(yytext);
      return TOK_BLOCK; }




[a-zA-Z0-9_,]+    { yylval.sval = strdup(yytext);
      return TOK_STRING; }


{SPACE}*          { return TOK_SPACE; }




^ENDS(.*)$        {}


^{CRLF}                         { return TOK_EMPTY_LINE; }
{CRLF}                          {}
.                               {}/* ignore unknown chars */
\n                      { ++line_num; return ENDL; }

yacca.y

%{
#include <cstdio> 
#include <cstring>
#include <iostream>
#include <stdio.h>

#define YYDEBUG 1

using namespace std;

extern "C" int yylex();
extern "C" FILE *yyin;
extern int line_num;


void yyerror(const char* s);
%}

// Symbols.
%union
{
    char* sval;
};

%token <sval> TOK_NAME
%token <sval> TOK_SIZE
%token <sval> TOK_STRING
%token <sval> TOK_ITERATE
%token <sval> TOK_DIRECTION
%token <sval> TOK_STRAP
%token <sval> TOK_WRAP
%token <sval> TOK_VIA
%token <sval> TOK_EMPTY_LINE 
%token <sval> TOK_BLOCK
%token <sval> TOK_LINE
%token <sval> TOK_BEGIN
%token <sval> TOK_END
%token TOK_SPACE
%token END ENDL



%%

language : program ;


program : block
| program block
;

block   : TOK_BEGIN TOK_BLOCK TOK_SPACE TOK_STRING blockcontents TOK_END TOK_SPACE TOK_STRING 
  {
    cout << endl << "SHAILAVI" <<  << " ";

  }
;


blockcontents : item
      | blockcontents item
      ;


item    :   TOK_SPACE TOK_NAME TOK_SPACE TOK_STRING         
    { 
        cout << endl << "Value:" <<  << "->" <<  << "  "; 
    }
    | TOK_SPACE TOK_SIZE TOK_SPACE TOK_STRING        { cout <<  << "->" <<  << "  "; }
    | TOK_SPACE TOK_ITERATE TOK_SPACE TOK_STRING     { cout <<  << "->" <<  << "  ";  }
    | TOK_SPACE TOK_DIRECTION TOK_SPACE TOK_STRING   { cout <<  << "->" <<  << "  " << endl; }
    | TOK_SPACE TOK_STRAP TOK_SPACE TOK_STRING       { cout << "ref:" <<  << "->" <<  << "  "; }
    | TOK_SPACE TOK_WRAP TOK_SPACE TOK_STRING    { cout <<  << "->" <<  << "  "; }
    | TOK_SPACE TOK_VIA TOK_SPACE TOK_STRING     { cout <<  << "->" <<  << "  " << endl; }
    ;



%%



int main(void) {
    FILE * pt = fopen("file", "r" );
    if(!pt)
    {
    cout << "Bad Input.Noexistant file" << endl;
    return -1;
    }
    yyin = pt;
    do
    {
    yydebug = 1;
        yyparse();
    }while (!feof(yyin));      
}
void yyerror(const char *s) {
    cout << "parse error on line " << line_num << "!  Message: " << s << endl;
    exit(-1);
}


#include "lex.yy.c"

编译步骤：

flex lexa.l
bison -d yacca.y
g++ yacca.tab.c -lfl -o scanner.exe

在执行时它给出 syntax error near blockcontents

请帮我找出我犯的错误。

非常感谢。

Answer 1

我花了一段时间，但我找到了缺陷。

在你的词法分析器中，你跳过了所有的制表符和空格序列（第一条规则）。但是您的解析器时不时地期望 white space 。因此语法错误。

因为你没有对白色 space 做任何事情，所以只需在词法分析器中吃掉它们（实际上你现在已经这样做了，但最好消除 {SPACE}*规则）并消除解析器中的 TOK_SPACE。

----编辑给出一些提示----

我为追踪错误所做的工作是：

使词法分析器冗长我添加了（省略了井号；由于某种原因它混淆了渲染器）


         #ifdef DEBUG
         #define RETURN(x)       cerr << "\n--> found " << #x << "\n"; return x;
         #else
         #define RETURN(x)       return x;
         #endif

并将所有 "return something" 替换为 RETURN(something)

我分别编译 bison/flex 个文件，然后 link 它们


    flex lexa.l && \
    bison -d yacca.y && \
    g++ -c -DDEBUG -I . lex.yy.c && \
    g++ -c -I . yacca.tab.c && \
    g++ lex.yy.o yacca.tab.o -o scanner

（在此处处理 linux）

根据工作示例的要求


    %{
    #include <cstdio>
    #include <cstring>
    #include <iostream>
    #include <stdio.h>

    #define YYDEBUG 1

    using namespace std;

    extern "C" int yylex();
    extern "C" FILE *yyin;
    extern int line_num;


    void yyerror(const char* s);
    %}

    // Symbols.
    %union
    {
        char* sval;
    };

    %token  TOK_NAME
    %token  TOK_SIZE
    %token  TOK_STRING
    %token  TOK_ITERATE
    %token  TOK_DIRECTION
    %token  TOK_STRAP
    %token  TOK_WRAP
    %token  TOK_VIA
    %token  TOK_EMPTY_LINE
    %token  TOK_BLOCK
    %token  TOK_LINE
    %token  TOK_BEGIN
    %token  TOK_END
    %token END ENDL

    %%

    language : program ;


    program : block
    | program block
    ;

    block   : TOK_BEGIN TOK_BLOCK TOK_STRING blockcontents TOK_END TOK_STRING 
      {
        cout << endl << "SHAILAVI" <<  << " ";

      }
    ;


    blockcontents : item
          | blockcontents item
          ;


    item    :   TOK_NAME TOK_STRING         { cout << endl << "Value:" <<  << "->" <<  << "  "; }
        | TOK_SIZE TOK_STRING        { cout <<  << "->" <<  " <<  " <<  " <<  << "  "; }
        | TOK_WRAP TOK_STRING    { cout <<  << "->" <<  << "  "; }
        | TOK_VIA TOK_STRING     { cout <<  << "->" <<  << "  " << endl; }
        ;

    %%

    int main(void) {
        FILE * pt = fopen("./input", "r" );
        if(!pt)
        {
        cout << "Bad Input.Nonexistent file" << endl;
        return -1;
        }
        yyin = pt;
        do
        {
        yydebug = 1;
            yyparse();
        }while (!feof(yyin));
    }
    void yyerror(const char *s) {
        cout << "parse error on line " << line_num << "!  Message: " << s << endl;
        exit(-1);
    }
    extern "C" int yywrap()
    {
            return (1 == 1);
    }

和词法分析器


    %{
    #include 
    #include 
    const char s[2] = " ";
    #include "yacca.tab.h"
    char *token;
    #define YY_DECL extern "C" int yylex()
    int line_num = 1;

    #ifdef DEBUG
    #define RETURN(x)       cerr << "\n--> found " << #x << "\n"; return x;
    #else
    #define RETURN(x)       return x;
    #endif


    using namespace std;
    %}

    DOT             "."
    COLON           ":"
    SEMICOLON       ";"
    COMMA           ","
    ANGLE_LEFT      ""
    AT              "@"
    EQUAL           "="
    SQUARE_OPEN     "["
    SQUARE_CLOSE    [^\]"]"
    OPENBRACE       "\("
    CLOSEBRACE      "\)"
    QUOTE           "\""
    QUOTE_OPEN      "\""
    QUOTE_CLOSE     [^\]"\""
    SPACE           " "
    TAB             "\t"
    CRLF            "\r\n"
    QUOTED_PAIR     "\"[^\r\n]
    DIGIT           [0-9]
    ALPHA           [a-zA-Z]
    QTEXT           [0-9a-zA-Z!#$%&'()*+,\-.\/:;?@\[\]^_`{|}~]


    /* [ \t]         ; */
    %%

    ^BEGIN(.*)\r?\n+\s*BEGIN(.*)     {   printf("\nError : two continous BEGIN is not allowed : "); }

    ^ENDS(.*)\r?\n+\s*ENDS(.*)   {   printf("\nError : two continous END is not allowed : \n"); }




    NAME          {  yylval.sval = strdup(yytext);
        RETURN(TOK_NAME); }

    SIZE          { yylval.sval = strdup(yytext);
          RETURN(TOK_SIZE); }

    ITERATE       { yylval.sval = strdup(yytext);
           RETURN(TOK_ITERATE); }

    DIRECTION   { yylval.sval = strdup(yytext);
          RETURN(TOK_DIRECTION); }

    STRAP       { yylval.sval = strdup(yytext);
          RETURN(TOK_STRAP); }

    WRAP        { yylval.sval = strdup(yytext);
          RETURN(TOK_WRAP); }

    VIA     { yylval.sval = strdup(yytext);
          RETURN(TOK_VIA); }

    ENDS        { yylval.sval = strdup(yytext);
          RETURN(TOK_END); }

    BEGIN       { yylval.sval = strdup(yytext);
          RETURN(TOK_BEGIN); }

    BLOCK       { yylval.sval = strdup(yytext);
          RETURN(TOK_BLOCK); }


    [a-zA-Z0-9_,]+    { yylval.sval = strdup(yytext); RETURN(TOK_STRING); }

    ^ENDS(.*)$        {}


    ^{CRLF}                         { RETURN(TOK_EMPTY_LINE); }
    {CRLF}                          {}
    .                               {}/* ignore unknown chars */
    \n                      { ++line_num; /* RETURN(ENDL); */ }

只剩下一个问题了。它真的不喜欢 EOF。我会把它留作练习。

使用 flex 和 bison 解析文件时出现语法错误

Syntax error while parsing file using flex and bison

parsing

block

flex-lexer

bisonc++