c - 使用malloc两次后为"A heap has been corrupted"

Question

我有一个正在尝试构建的“单词”链接列表，我创建了一个名为“add_to_mem”的函数，它将下一个单词添加到链接列表中。我对代码进行了几次检查，发现他工作了两次 - 一次当链接列表为 NULL 时，一次当它不是 NULL 时 - 它确实工作，但在我第三次调用时该方法 - 我收到“堆已损坏”错误。代码:

    typedef struct { unsigned int val : 14; } word;

    typedef struct machine_m

    {

    word * current;
    int line_in_memo;
    char * sign_name;

    struct machine_m * next_line;
}Machine_Memo;

功能:

    /*Adding a word to the memory.*/
void add_to_mem(word * wrd, int line, char * sign_name)
{
    Machine_Memo * temp = NULL, *next = NULL;
    if (machine_code == NULL)
    {

        machine_code = (Machine_Memo *)malloc(sizeof(Machine_Memo));
        if (machine_code == NULL)
        {
            printf("Memory allocation has failed.");
            exit(1);
        }
        machine_code->current = wrd;
        machine_code->line_in_memo = line;
        machine_code->sign_name = sign_name;
        machine_code->next_line = NULL;

    }
    else
    {
        printf("token has been reached");
        temp = machine_code;
        next = (Machine_Memo *)malloc(sizeof(Machine_Memo)); //Line of error
        if (next == NULL)
        {
            printf("MEMORY ALLOCATION HAS FAILED. EXITING PROGRAM.\nThe problem has occured on code line %d", 775);
            exit(0);
        }
        next->current = wrd;
        next->line_in_memo = line;
        next->sign_name = sign_name;
        next->next_line = NULL;

        while (temp->next_line != NULL)
        {
            temp = temp->next_line;
            temp->next_line = next;

        }


    }
}

Answer 1

据我了解代码，它不会创建链表。它创建节点，但不将它们链接在一起。

第一次调用时，会创建 machine_code(列表头)。在下一次调用时，将创建节点“next”，但是循环:

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

不执行任何操作，因为“machine_code->next”值为空。所以循环内的代码不会被执行。我们在这里得到的不是一个链接列表，而是零星的节点，这些节点没有相互连接。你可能想要(正如这里另一篇文章所指出的那样)有类似的东西:

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