c - 使用堆栈或 atoi() 时出现运行时错误

Question

#define MAXL 256

第一遍:in = "25 7 * 14 - 6 +"; 顺利运行，答案正确。

第二遍:in = "1 24 3 + * 41 -"; 程序在输出 Num got in: 41 后立即停止 预期:继续循环并进入减号，然后 pop(s) 并减去 41

我猜测我的程序耗尽了分配的空间，因为 free() 没有按照我的预期完成工作，但我不确定。

任何帮助将不胜感激。谢谢!

double evaluatePost(char * in)
{
    double * op1 = NULL, * op2 = NULL, * msgr = NULL;
    int i, j;
    char * c = {0}, tempExp[MAXL] = {0}; 
    char ** token = NULL;
    Stack * s = createStack();

    strcpy(tempExp, in);        /* Copy in to a temporary array so strtok will not destroy in */

    for(c = strtok(tempExp, " "); c != NULL; ++i, c = strtok(NULL, " "))
    {
        if(isdigit(c[0]))
        {
            printf("\nNum got in: %s\n", c); /* Crash right after this line output 41 */
            system("PAUSE");
            msgr = (double*)malloc(sizeof(double)); /* I made a malloc check here, it never showed error */
            *msgr = atoi(c); /* I don't know if it crash at this line or the next one */
            push(s, msgr);  /* stack has no limit, receives stack* and void* */
            /* It never got pass to here after output 41 */
        }
        else
        {
            op2 = (double *)pop(s);
            op1 = (double *)pop(s);
            printf("\n%f %f %s\n", *op1, *op2, c);
            system("PAUSE");
            msgr = (double*)malloc(sizeof(double));
            if(!msgr)
            {
                printf("Memory allocation failed.\n");
                system("PAUSE");
                exit(1);
            }
            switch(*c)
            {
                case '+': *msgr = (*op1 + *op2); break;
                case '-': *msgr = (*op1 - *op2); break;
                case '*': *msgr = (*op1 * *op2); break;
                case '/': *msgr = (*op1 / *op2); break;
            }
            printf("\n%.1f\n", *msgr);
            system("PAUSE");
            /* Free the memory before they become orphans */            
            free(op1), free(op2);
            push(s, msgr);
        }       
    }   
    returnVal = *((double *)pop(s));
    makeEmpty(s);

    return returnVal;
}
void push(Stack * stack, void * dataInPtr)
{
    /* Define a new StackNode */
    StackNode * newPtr;

    /* Get some Memory */
    newPtr = (StackNode*)malloc(sizeof(StackNode));
    if(!newPtr)
    {
        printf("Out of memory");
        system("PAUSE");
        exit(1);
    }   
    /* Assign dataIn to dataPtr */
    newPtr->dataPtr = dataInPtr;

    /* Make the links */
    newPtr->link = stack->top;  /* Point both to top */
    stack->top = newPtr;        /* newPtr at top pointed to be head */
    (stack->count)++;
}
void * pop(Stack * stack)
{
    /* Hold the data */
    void * dataOutPtr;
    StackNode * temp;

    /* Check if stack is empty */
    if(stack->count == 0)
        dataOutPtr = NULL;
    else
    {
        /* Get the data and remove the node */
        temp = stack->top;                  /* temp points to top */
        dataOutPtr = stack->top->dataPtr;   /* dataOutPtr has data */
        stack->top = stack->top->link;      /* stack moves to next node */
        temp->link = NULL;                  /* break top node off stack */
        free(temp);                         /* frees memory */
        (stack->count)--;                   
    }
    return dataOutPtr;
}
typedef struct node
{
    void * dataPtr;
    struct Node * link;
} StackNode;

typedef struct
{
    int count;
    StackNode * top;
} Stack;

Answer 1

您的问题可能出在这里:

您正在 pop() 中释放 Stack 节点

temp = stack->top;                  /* temp points to top */
dataOutPtr = stack->top->dataPtr;   /* dataOutPtr has data */
stack->top = stack->top->link;      /* stack moves to next node */
temp->link = NULL;                  /* break top node off stack */
free(temp);                         /* frees memory */

之后，您将在 evaluatePost() 中释放节点中的数据指针:

free(op1), free(op2);

释放内存的顺序应始终与malloc相反，即您应先分配 Node，然后分配节点数据，然后再分配 free > 首先释放节点数据，然后释放节点本身。

您遇到的是某些输入的问题，而不是其他输入的问题，因为这是未定义的行为。

要了解更多关于C中未定义行为的信息，可以在SO中搜索相关问题。