Flex/Bison 错误：请求非结构或联合中的成员“str”

我正在学习 flex/bison。我编写了以下程序但出现错误。

%{
#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;}

我收到的错误：

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？

第一个明显的问题是你不应该定义YYSTYPE如果您正在使用 yacc。 Yacc 定义YYSTYPE从你的%union。你需要定义YYSTYPE如果你正在使用lex，但不使用yacc.

Your %union解析堆栈项类型仅包含int and str成员。示例：您已经定义了exp语法符号具有类型str，然后你就得到了这个产生式：

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

The mknode函数返回node *，但是类型$$符号是char *因为它代表的是exp在左侧，您输入的是str，以及str的成员%union is char *.

论据mknode也必须是node *. But $1 and $3没有那种类型。