Flex/Bison错误:在非结构或联合中请求成员"str" [英] Flex/Bison Error:request for member `str' in something not a structure or union

问题描述

我正在学习弹性/野牛.我编写了以下程序，但出现错误.

I'm learning flex/bison. I wrote the following program but getting errors.

%{
#include <stdio.h>

typedef struct node
{
    struct node *left;
    struct node *right;
    char *token;

}node;

node *mknode( node *left, node *right, char *token);
void printtree(node *tree);

#define YYSTYPE struct node *

%}


%union 
{
    char* str;
    int num;
}


%start  lines
%token <str> WORD 
%token <str> PLUS MINUS TIMES DIVIDE    POWER
%token <str> LEFT_PARENTHESIS RIGHT_PARENTHESIS
%token  <str> END

%left PLUS MINUS
%left TIMES DIVIDE
%right POWER

%type <str> exp term factor line lines
%%

lines:      /* empty */
            | lines line;

line:       exp END                 { printtree($1); printf("\n");}
            ;

exp:        term                    {$$=$1; }
            | exp PLUS term         { $$=mknode($1,$3,"+"); }
            | exp MINUS term        { $$=mknode($1,$3,"-"); }
            ;

term:       factor                  { $$=$1; }
            |term TIMES factor      { $$=mknode($1,$3,"*"); }
            ;

factor:     WORD                    { $$=mknode(0,0, (char*)yylval); }
            |LEFT_PARENTHESIS exp RIGHT_PARENTHESIS 
                                    { $$=$2; }
            ;
%%

int main(void)
{
    return yyparse();
}

node *mknode(node *left, node *right, char *token)
{
  /* malloc the node */
  node *newnode = (node *)malloc(sizeof(node));
  char *newstr = (char *)malloc(strlen(token)+1);
  strcpy(newstr, token);
  newnode->left = left;
  newnode->right = right;
  newnode->token = newstr;
  return(newnode);
}

void printtree(node *tree)
{
  int i;

  if (tree->left || tree->right)
    printf("(");

  printf(" %s ", tree->token);

  if (tree->left)
    printtree(tree->left);
  if (tree->right)
    printtree(tree->right);

  if (tree->left || tree->right)
    printf(")");
}

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

flex:

%{

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

%}

%%

[a-zA-Z0-9]+            { yylval.str = strdup( yytext ); return WORD; }
                        /* cast pointer to int for compiler warning */
[ \t]                   ;
"+"                     return(PLUS);
"-"                     return(MINUS);
"*"                     return(TIMES);
"/"                     return(DIVIDE);
"^"                     return(POWER);
"("                     return(LEFT_PARENTHESIS);
")"                     return(RIGHT_PARENTHESIS);
\n                      return(END);


%%

int yywrap (void) {return 1;}

我得到的错误:

C:\flexbison>recomp example2
example2.y:40.6: warning: empty rule for typed nonterminal, and no action
conflicts: 5 reduce/reduce
example2.y:43: error: request for member `str' in something not a structure or union
example2.y:46: error: request for member `str' in something not a structure or union
example2.y:46: error: request for member `str' in something not a structure or union
example2.y:47: error: request for member `str' in something not a structure or union
example2.y:47: error: request for member `str' in something not a structure or union
example2.y:47: error: request for member `str' in something not a structure or union
example2.y:48: error: request for member `str' in something not a structure or union
example2.y:48: error: request for member `str' in something not a structure or union
example2.y:48: error: request for member `str' in something not a structure or union
example2.y:51: error: request for member `str' in something not a structure or union
example2.y:51: error: request for member `str' in something not a structure or union
example2.y:52: error: request for member `str' in something not a structure or union
example2.y:52: error: request for member `str' in something not a structure or union
example2.y:52: error: request for member `str' in something not a structure or union
example2.y:55: error: request for member `str' in something not a structure or union
example2.y:56: error: request for member `str' in something not a structure or union
example2.y:58: error: request for member `str' in something not a structure or union
example2.y:58: error: request for member `str' in something not a structure or union

知道为什么我会收到此错误吗?

Any idea why I'm getting this error?

推荐答案

第一个明显的问题是，如果您使用的是yacc，则不应该定义YYSTYPE. Yacc从您的%union定义YYSTYPE.如果使用的是lex，而不是yacc，则需要定义YYSTYPE.

The first glaring problem is that you should not be defining YYSTYPE if you are using yacc. Yacc defines YYSTYPE from your %union. You need to define YYSTYPE if you're using lex, but not using yacc.

您的%union解析堆栈项目类型仅包含int和str成员.例如:您已将exp语法符号定义为具有str类型，然后具有以下形式:

Your %union parse stack item type only contains int and str members. Example: you have defined the exp grammar symbol as having type str, and then you have this production:

exp:        term                    {$$=$1; }
            | exp PLUS term         { $$=mknode($1,$3,"+"); }
            | exp MINUS term        { $$=mknode($1,$3,"-"); }
            ;

mknode函数返回node *，但是$$符号的类型为char *，因为它代表左侧的exp(您键入为str)，并且%union的str成员是char *.

The mknode function returns node *, but the type of the $$ symbol is char * because it stands for the exp on the left hand side, which you typed as a str, and the str member of the %union is char *.

mknode的参数也必须为node *.但是$1和$3没有这种类型.

The arguments to mknode must also be node *. But $1 and $3 do not have that type.

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