c - 打印出链表的输入 [C]

Question

我编写了一个链接列表并设法向其中添加文件支持。现在命令提示符输出有问题。最后的 pokemon->name 和 pokemon->number 输出很神秘。不知何故，我认为我在将最后一批数据保存到内存中时犯了一个错误，因为它实际上是正确保存到文件中的。

这是代码(代码后输入测试)

pokemonPtr addPokemon(void){

FILE *filePtr;

//filePtr = fopen ("pokedex.txt", "a");

//if (filePtr == NULL){
    filePtr = fopen ("pokedex.txt","w");
//}

pokemonPtr firstPtr;
pokemonPtr thisPokemon;
firstPtr = NULL;

firstPtr = (pokemon *) malloc(sizeof(pokemon));
firstPtr->name = (char *) malloc(sizeof(char) * POKEMON_LENGTH);

printf ("Enter the name of the Pokemon.\n");
scanf("%s",firstPtr->name);
fprintf(filePtr, "Pokemon Name:%s    ", firstPtr->name);
getchar();
printf ("Enter the number of the Pokemon.\n");
scanf("%d",&firstPtr->number);
fprintf(filePtr, "Pokemon Nummer:%d\n", firstPtr->number);



firstPtr->next = (pokemon *) malloc(sizeof(pokemon));

thisPokemon = firstPtr->next;

int i = 0;

while (i < 2){

    thisPokemon->name = (char *) malloc(sizeof(char) * POKEMON_LENGTH);

    printf ("Enter the name of the Pokemon.\n");
    scanf("%s",thisPokemon->name);
    fprintf(filePtr, "Pokemon Name:%s    ", thisPokemon->name);
    printf ("Enter the number of the Pokemon.\n");
    scanf("%d",&thisPokemon->number);
    fprintf(filePtr, "Pokemon Nummer:%d\n", thisPokemon->number);

    thisPokemon->next =(pokemon *) malloc (sizeof(pokemon));
    thisPokemon = thisPokemon->next;

    i++;

}

thisPokemon->next = NULL;

fclose (filePtr);

return firstPtr;

}

void showPokemon(pokemonPtr firstPtr){

printf ("Name:   %s\n"
        "Nummer: %d\n", firstPtr->name, firstPtr->number);

pokemonPtr thisPokemon = firstPtr->next;

while (thisPokemon != NULL){

    printf ("Name:   %s\n"
            "Nummer: %d\n", thisPokemon->name, thisPokemon->number);

    thisPokemon = thisPokemon->next;
}


}

我尝试的输入是:

Pokemon Name:dudu Pokemon Nummer:3
Pokemon Name:dada Pokemon Nummer:3
Pokemon Name:dudi Pokemon Nummer:23
The output in cmd was:
Name: dudu
Nummer: 3
Name: dada
Nummer: 3
Name: dudi
Nummer: 23
Name: Ót
Nummer: 7607776

这里发生了什么？

Answer 1

好吧，问题出在你构建链接列表的方式上 - 一旦你在调试器下执行代码，它就变得微不足道了 -> 你真的应该学会这样做;-)

您正确地将头部保存在 firstPtr 中，但您以空但已创建的链接元素开始循环。所以这是 addPokemon 中发生的事情:

• 初始部分:分配一个新项目并读取其值分配一个新项目并将其链接到第一个:first(dudu) -> this(empty)
• 第一次传入循环:first(dudu) -> dada ->empty
• 循环中的第二次传递:first(dudu) -> dada -> dudi ->empty
• 循环结束后，你输入了一个 null，但一步太远了:first(dudu) -> dada-> dudi ->empty -> NULL

如何修复:

您应该在将值存储在循环中之前在循环中分配一个新项目，并使用 thisPokemon 指向firstPokemon 来启动循环:

...
firstPtr->next = NULL;

thisPokemon = firstPtr;

int i = 0;

while (i < 2){

    thisPokemon->next =(pokemon *) malloc (sizeof(pokemon));
    thisPokemon = thisPokemon->next;
    thisPokemon->name = (char *) malloc(sizeof(char) * POKEMON_LENGTH);

    printf ("Enter the name of the Pokemon.\n");
    scanf("%s",thisPokemon->name);
    fprintf(filePtr, "Pokemon Name:%s    ", thisPokemon->name);
    printf ("Enter the number of the Pokemon.\n");
    scanf("%d",&thisPokemon->number);
    fprintf(filePtr, "Pokemon Nummer:%d\n", thisPokemon->number);

    i++;

}
...