Question

I'm trying to make a linked list, where each node stores a string, but I'm having a problem where each node ends up storing the same exact string in every single node. At the end of main(), I print out the word stored in each node, and it always just repeats the last string entered for the entire list.

I don't have any clue what is happening, because if I make it a string of characters it works perfectly fine, where each character is stored in the correct node.

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

struct wordnode {
    char *word;
    struct wordnode *next;
};

struct wordnode *link = NULL;

void addword(char *aword);

int main(void) {


    char *aword;
    int i;

    for(i = 0; i < 10; i++) {
        scanf(" %s", aword);
        addword(aword);
    }
    printf("\n");
    for(; link != NULL; link = link->next) {
        printf("|%s ", link->word);
    }

    printf("|\n");
    return 0;
}

void addword(char *aword) {
    struct wordnode *cur, *prev, *new_node;

    new_node = malloc(sizeof(struct wordnode));

    new_node->word = aword;

    for(cur = link, prev = NULL; cur != NULL; prev = cur, cur = cur->next) {
        ;
    }

    new_node->next = cur;

    if(prev == NULL) {
        link = new_node;
    } else {
        prev->next = new_node;
    }
}

Answer 1

There are many problems in the code. Some of them are already mentioned. The code will be something like this. Explanation at the end of the code.

<input formControlName="value" placeholder="Valor" [matDatepicker]="myDatepicker">

You wanted to store some string (nul terminated char array) and then you wanted to add them in the list. Also from your example implementation you were trying to add it in the list at the tail.

To sum up -

#include <stdio.h> #include <string.h> #include <stdlib.h> #define STR2(x) #x #define STR(X) STR2(X) #define MAXWORD 10 #define MAXWORDLEN 20 struct wordnode { char *word; struct wordnode *next; }; struct wordnode* addword(char *aword, struct wordnode *link); void printList(struct wordnode*link); void freeList(struct wordnode *link); int main(void) { char aword[MAXWORDLEN+1]; struct wordnode *link = NULL; for(size_t i = 0; i < MAXWORD; i++) { if( scanf("%" STR(MAXWORDLEN) "s", aword[i]) == 1 ){ link = addword(aword, link); } else{ fprintf(stderr, "%s\n","Error in input" ); exit(1); } } printList(link); freeList(link); return 0; } void printList(struct wordnode*link){ while(link){ printf("%s \n", link->word); link = link->next; } } void freeList(struct wordnode *link){ struct wordnode *temp; while(link){ temp = link; link = link->next; free(temp); } } struct wordnode* addword(char *aword, struct wordnode *link) { struct wordnode *new_node = malloc(sizeof(struct wordnode)); if( new_node == NULL){ fprintf(stderr, "%s\n", "Error in malloc"); exit(1); } new_node->word = strdup( aword ); if( new_node->word == NULL){ fprintf(stderr, "%s\n", "Error in strdup" ); exit(1); } new_node->next = NULL; if( link == NULL){ return new_node; } struct wordnode *cur = link; while( cur->next != NULL ){ cur = cur -> next; } cur->next = new_node; return link; } demands a pointer to some memory where it can store inputted data. But yours were uninitialized.
secondly the way you were copying strings, it was just a shallow copy (you were making it point to some already existing memory). You need copy it either using scanf or strdup or malloc - memcpy.
In case POSIX malloc-strcpy is not available, you can use what Jonathan Leffler mentioned.
Here you can see that we have freed the allocated memory using strdup() function. When you are done working with the memory you allocated- free the memory.
Don't cast the return value of freeList().
Also check whether the malloc is successful checking it's return value.
You have used the list head as the global variable. It is not needed here.

Answer 2

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.js"></script> <script type="text/javascript" src="js/bootstrap.js"></script> is not initialized and located. It should be:

char * aword

(100 is just a number, size of array. You can replace it with any number what you want)

Answer 3

您尚未为字符串分配内存。因此aword将包含垃圾值并将其传递给scanf是一种未定义的行为。假设aword有0x7fffe4e0cdf0，而您的scanf将字符串存储在地址0x7fffe4e0cdf0，并将此地址传递给addword函数和您的结构成员{{1也使用相同的值更新。下一个scanf还将新值存储在word指向的同一内存中并传递给该函数。因此，所有链接列表中的aword都指向相同的内存位置。理想的解决方案是为每个被扫描的字符串分配内存，并将其传递给“addword”函数。

Linked list of strings has the same strings for each node

3 个答案: