將令牌分配給結構節點型別變數后，令牌為空-有解無憂

我正在解決這個奇怪的問題（至少對我來說）我正在使用 lex 和 yacc 創建一個 AST，而所有標記都可以作業并且語法也可以正常作業（我只用列印測驗了它）當我嘗試分配時一個變數的新節點，只是為了測驗我試圖列印節點的令牌，每次我嘗試它時令牌只是（空）例如這是我的代碼的一部分：

ifelse: IF LEFTBRACKET cond RIGHTBRACKET LEFTBLOCK body RIGHTBLOCK {$$ = mknode("IF",$3,$6);printf("token is %s\n",$$->token);}

mknode 函式是這樣作業的：

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

所以對于這個例子，這是輸出：

token is (null)

知道為什么它保持為空嗎？如果重要的話，我正在將 VMWare 與 Ubuntu 20.04 一起使用

完整的 lex 檔案：

%{
#include "y.tab.h"
#include <stdio.h>
#include <string.h>
%}

%%
"\"" {printf("LEX: double quote here\n");return DQUOTE;}
"\'" {printf("LEX: single quote here\n");return SQUOTE;}
"}" {printf("LEX: } here\n");return RIGHTBLOCK;}
"{" {printf("LEX: { here\n");return LEFTBLOCK;}
";" {printf("LEX: ; here\n");return SEMICOLON;}
"," {printf("LEX: comma here\n");return COMMA;}
"(" {printf("LEX: opening bracket here\n");return LEFTBRACKET;}
")" {printf("LEX: closing bracket here\n");return RIGHTBRACKET;}


&& {printf("LEX: and here\n");return AND;}
"||" {printf("LEX: || here\n");return OR;}
"=" {printf("LEX: assign here\n");return ASSIGN;}
== {printf("LEX: == here\n");return EQ;}
">" {printf("LEX: > here\n");return GT;}
">=" {printf("LEX: >= here\n");return GTEQ;}
"<" {printf("LEX: < here\n");return LT;}
"<=" {printf("LEX: <= here\n");return LTEQ;}
"-" {printf("LEX: - here\n");return SUB;}
"!" {printf("LEX: ! here\n");return NOT;}
"!=" {printf("LEX: != here\n");return NOTEQ;}
"/" {printf("LEX: div here\n");return DIV;}
" " {printf("LEX: add here\n");return ADD;}
"*" {printf("LEX: mul here\n");return MUL;}
"&" {printf("LEX: & here\n");return ADRS;}

if {printf("LEX: if here\n");return IF;}
else {printf("LEX: else here\n");return ELSE;}

do {printf("LEX: do here\n");return DO;}
while {printf("LEX: while here\n");return WHILE;}
for {printf("LEX: for here\n");return FOR;}

var {printf("LEX: var here\n");return VAR;}
return {printf("LEX: return here\n");return RETURN;}
null {printf("LEX: nullval here\n");return NULLVAL;}

void {printf("LEX: func return type here\n");return VOID;}
"int*" {printf("LEX: int* type here\n");return INTPOINT;}
"char*" {printf("LEX: char* type here\n");return CHARPOINT;}
"real*" {printf("LEX: real* type here\n");return REALPOINT;}
int {printf("LEX: int type here\n");return INT;}
real {printf("LEX: real type here\n");return REAL;}
char {printf("LEX: char type here\n");return CHAR;}
bool {printf("LEX: bool type here\n");return BOOL;}
"true"|"false" {printf("LEX: boolval here\n");return BOOLVAL;}
[0-9]  {yylval.string = yytext;printf("LEX: int val here\n");return INTVAL;}
"-"|0|[1-9][0-9] "."[0-9] |[1-9][0-9] '.'[0-9]['E'|'e'][' '|'-'][0-9]  {printf("LEX: realval here\n");yylval.string = strdup(yytext);return REALVAL;}
[a-zA-Z][0-9]*"_"[a-zA-Z]* {printf("LEX: ID here\n");yylval.string = strdup(yytext);return ID;}
[a-zA-Z] {printf("LEX: char here\n");yylval.string = strdup(yytext);return CHARVAL;}
[a-zAZ]*[0-9]*[a-zAZ] [0-9]*[a-zAZ]* {printf("LEX: string here\n");yylval.string = strdup(yytext);return STRING;}
. ;
%%

完整的 yacc 檔案：

%{
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <string.h>

#include "lex.yy.c"
int yyerror();
typedef struct node
{
char* token;
struct node *left;
struct node *right;
}node;

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

%union
{
    struct node *node;
    char* string;
}    

%token <string> DIV ADD MUL SUB AND NOT OR RETURN ASSIGN
%token <string> EQ GT GTEQ LT LTEQ NOTEQ SEMICOLON COMMA LEFTBRACKET RIGHTBRACKET RIGHTBLOCK LEFTBLOCK
%token <string> ID CHARVAL INTVAL REALVAL BOOLVAL STRING ADRS DQUOTE SQUOTE 
%token <node> INT REAL BOOL CHAR VOID INTPOINT CHARPOINT REALPOINT VAR NULLVAL 
%token <node> IF ELSE WHILE DO FOR 

%type <string> name oper type rettype ret
%type <node> code ifelse body action args argnum math cond params block valvar

%left SEMICOLON COMMA RIGHTBRACKET RIGHTBLOCK
%right LEFTBLOCK 
%%
st: code {printf("YACC: Code done!\n");}

code: rettype name params block code {
    $$ = mknode("(FUNC",mknode($2,mknode("(ARGS",$3,NULL),mknode("(RET",mknode($1,NULL,NULL),NULL)),mknode("(BODY",$4, NULL));
    printf("YACC: func ready\n");}| {}

params: LEFTBRACKET args RIGHTBRACKET {$$ = $2;}
        

block: LEFTBLOCK code RIGHTBLOCK {$$ = $2;}| 
       LEFTBLOCK body RIGHTBLOCK {$$ = $2;}| 
       LEFTBLOCK code body RIGHTBLOCK {$$ = mknode("",$2,$3);}

ifelse: IF LEFTBRACKET cond RIGHTBRACKET LEFTBLOCK body RIGHTBLOCK {$$ = mknode("IF",$3,$6);printf("token is %s\n",$$->token);printf("YACC: if ready\n");}|
        IF LEFTBRACKET cond RIGHTBRACKET LEFTBLOCK body RIGHTBLOCK ELSE LEFTBLOCK body RIGHTBLOCK {$$ = mknode("IF",$3,mknode("",$6,mknode("ELSE",$10,NULL)));
            printf("YACC: if else ready\n");}

rettype:VOID {$$ = "VOID";}|
        type {$$ = $1;}

name: STRING {$$ = $1;}|
      CHARVAL {$$ = $1;}

args: type argnum {$$ = mknode($1,mknode(" ",NULL,NULL),$2);}| 
      {$$ = mknode("",NULL,NULL);printf("YACC: args ready\n");}

argnum: name argnum {$$ = mknode($1,mknode(" ",NULL,NULL),$2);}| 
        COMMA argnum {$$ = mknode(" ",$2,NULL);}| 
        SEMICOLON args {$$ = mknode(" ",$2,NULL);}|  
        {$$ = NULL;printf("YACC: args num ready\n");}

type: INT {$$ = "INT";}|
      REAL {$$ = "REAL";}|
      CHAR {$$ = "CHAR";}|
      INTPOINT {$$ = "INT*";}|
      CHARPOINT {$$ = "CHAR*";}|
      REALPOINT {$$ = "REAL*";};

body: action body {$$ = mknode(" ",$1,$2);}|
       action {$$ = mknode(" ",$1,NULL);}| 
       ifelse  {$$ = mknode("(IF-ELSE",mknode("\n",NULL,NULL),$1);printf("YACC: block ready\n");}

action: name ASSIGN math {$$ = mknode($2,mknode($1,NULL,NULL),mknode(" ",$3,NULL));printf("YACC: action ready\n");}| 
        RETURN ret SEMICOLON {$$ = mknode("(RET",mknode($2,NULL,NULL),NULL);printf("YACC: return action ready\n");}

ret: INTVAL {$$ = $1;}| 
     SQUOTE CHARVAL SQUOTE {$$ = $2;}| 
     REALVAL {$$ = $1;}| 
     DQUOTE STRING DQUOTE  {$$ = $2;}| 
     name {$$ = $1;}| 
     ADRS name {$$ = $2;}

math: valvar oper math {$$ = mknode($2, $1,$3);}| 
      valvar SEMICOLON {$$ = mknode(" ",$1,NULL);}| 
      valvar math {$$ = mknode(" ",$1,$2);}

oper: ADD {$$ = " ";}|
      DIV {$$ = "/";}|
      SUB {$$ = "-";}|
      MUL {$$ = "*";}

cond: valvar EQ valvar {$$ = mknode($2,$1,$3);}| 
      valvar GT valvar {$$ = mknode($2,$1,$3);}| 
      valvar GTEQ valvar {$$ = mknode($2,$1,$3);}| 
      valvar LT valvar {$$ = mknode($2,$1,$3);}| 
      valvar LTEQ valvar {$$ = mknode($2,$1,$3);}| 
      valvar NOTEQ valvar {$$ = mknode($2,$1,$3);}

valvar: name {$$ = mknode($1,NULL,NULL);}|
        INTVAL {$$ = mknode($1,NULL,NULL);}
%%

int main(){
    return yyparse();
}

void printtree(node* tree){
    printf("%s\n", tree->token);
    if(tree->left)
        printtree(tree->left);
    if(tree->right)
        printtree(tree->right);
}

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


int yyerror(){
    printf("language error\n");
    return 0;
}

現在的輸入測驗代碼是：

void foo(int x){
    if (x==5){
        return 'a';
    }
}

uj5u.com熱心網友回復：

在許多其他問題中，您的mknode函式永遠不會設定newnode->token. 所以它是未定義的——你很幸運，它包含一個空值而不是一個會崩潰的無效指標。

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