C语言 崩溃遍历回双重链表

Question

typedef struct tape
{
    char symbol;
    struct tape *next;
    struct tape *prev;
}tape;
tape *pt;    
void GenerateInputTape(int n)
{
    int i;
    pt=(tape*)malloc(sizeof(tape));
    pt->symbol='B';
    pt->prev=NULL;
    pt->next=(tape*)malloc(sizeof(tape));
    pt=pt->next;
    for(i=0;i<2*(n+1);i++)
    {   
        if(i < (2*n/2))
            pt->symbol='0';
        else
            pt->symbol='1';
        pt->prev=pt;
        pt->next=(tape*)malloc(sizeof(tape));
        pt=pt->next;
    }
    pt->symbol='B';
    pt->next=NULL;
}
void ShowTape()
{
    //Move tape to the beginning
    while (pt->prev != NULL)
        pt=pt->prev; //crash point
    //List out all of the elements
    while ((pt->next) != NULL)
    {   
        printf("%c",pt->symbol);
        pt=pt->next;
    }
    puts("n");
}

这是一个程序代码片段，它被设计用来创建一个双链表，用B0…n011....(n+1)1B字符填充它并打印它们。不幸的是，它在返回时崩溃了。为什么?

turing_machine.exe中0x771a15de的未处理异常:0xC0000005:读取位置0xcdcdcdd5.

Answer 1

您没有正确设置pt->prev

不是

pt->prev=pt;
pt->next=(tape*)malloc(sizeof(tape));

试题:

pt->next = malloc(sizeof(tape));
pt->next->prev = pt;