打印链接列表会导致带有垃圾值的字符串 (C)

Question

我正在从 a.txt 文件中读取一个链表来填充以下节点：

typedef struct node {
    
    int data;
    char* line;
    struct node* next;

} NODE;

该代码工作正常并将文件读入链接列表。 我在初始化每个节点时打印出字符串。 但是，每当我调用printList() function 时， line字符串始终是垃圾值。 样品运行：

./a.out linkedlisttext.txt

data in readFile(): 4
string in readFile():  Hello world
address in readFile(): 0x1326067a0


data in readFile(): 28
string in readFile():  What is up world???
address in readFile(): 0x1326067c0


data in readFile(): 2124
string in readFile():  your mother
address in readFile(): 0x1326067e0


data in readFile(): 85
string in readFile():  more data
address in readFile(): 0x132606800


data in readFile(): 9421
string in readFile():  just a little more data
address in readFile(): 0x132606820


data in readFile(): 992
string in readFile():  are we almost there?
address in readFile(): 0x132606840


data in readFile(): 301
string in readFile():  we did it!
address in readFile(): 0x132606860

DATA:    4 | STRING �g`2
address in printList(): 0x1326067a0
DATA:   28 | STRING �g`2
address in printList(): 0x1326067c0
DATA: 2124 | STRING �g`2
address in printList(): 0x1326067e0
DATA:   85 | STRING h`2
address in printList(): 0x132606800
DATA: 9421 | STRING 0h`2
address in printList(): 0x132606820
DATA:  992 | STRING Ph`2
address in printList(): 0x132606840
DATA:  301 | STRING 
address in printList(): 0x132606860

这是linkedlisttext.txt

4, Hello world
28, What is up world???
2124, your mother
85, more data
9421, just a little more data
992, are we almost there?
301, we did it!

这是代码：

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

typedef struct node {
    
    int data;
    char* line;
    struct node* next;

} NODE;


struct node* readFile(FILE* fp, NODE* root) {
    char line[100];
    char* token;
    NODE* curr;
    NODE* prev;

    
    while(fgets(line, 100, fp) != NULL) {   
        
        curr = malloc(sizeof(struct node*));

        token = strtok(line, ",");
        
        curr->data = atoi(token);

        printf("\ndata in readFile(): %d\n", curr->data);
        
        token = strtok(NULL, "");
        curr->line = (char*) malloc(sizeof(token)  + 1);

        strcpy(curr->line, token);
        printf("string in readFile(): %s", curr->line);
        printf("address in readFile(): %p\n\n", curr->line);


        curr->next = NULL;  
    
        
        if(root == NULL) {
            root = curr;
        } else {
            NODE* travel = root;

            while(travel->next != NULL) {
                travel = travel->next;
            }

            travel->next = curr;

        }

        
    }

    return root;    

}

void printList(NODE* root) {
    
    struct node* temp = root;

    while(temp->next != NULL) {
        printf("DATA: %4d | STRING %s\n", temp->data, temp->line);
        printf("address in printList(): %p\n", temp->line);

        
        temp = temp->next;
    }

    printf("DATA: %4d | STRING %s\n", temp->data, temp->line);
    printf("address in printList(): %p\n", temp->line);

}

int main(int argc, char** argv) {
    
    FILE* fp = fopen(argv[1], "r");
    NODE* root = NULL;  

    if(fp == NULL) {
        return 0;
    }   

    root = readFile(fp, root);
    printList(root);
    
}

任何帮助表示赞赏，谢谢！

Answer 1

curr->line = (char*) malloc(sizeof(token) + 1);

由于sizeof(token)始终返回指针的大小（大多数系统为 8 个字节），而不是字符串的长度，因此您没有为line分配足够的缓冲区。 请尝试：

curr->line = malloc(strlen(token) + 1);

作为旁注，您对主 function 中的行缓冲区和结构成员名称使用相同的名称line 。 它们具有单独的名称空间并且在语法上有效，但可能会为将来的维护造成混淆。

Answer 2

这是高度怀疑的：

 curr = malloc(sizeof(struct node*));

您正在为struct node指针而不是为struct node分配 memory 。 鉴于 memory 大小的指针和整数，随后分配给curr->data可能实际上有效，但随后分配给curr->line和curr->next可能会给您带来麻烦。

或不。 未定义的行为本质上是不可预测的。