如何在给定位置取消引用空指针的内容

Question

在下面的Print方法中，调用Put方法后如何读取数组的内容？

    //put some "pointers" in an array
    Put(void* array)
    {
            void* ptr = array;              //get starting address of array

            int k;
            for(k=1; k <= 10; k++)
            {        
                //put data in array
                ptr = Get_DataPointer();    //sample return data: 0x6703fff00000 (64-bit hex)       
                ptr += k;                   //increment address for next iteration
            }
    }

//print the contents of the array
Print(void* array)
{
        for(k=0; k < 10; k++)
        {
            long dataPointer = ((long*)(array+ k));
            printf("Pointer %i, Content=%l\n", k, dataPointer);
        }
}

我在输出中得到“ 0”或“＆”。

Answer 1

它看起来应该更像

Put(void* array)
{
    long *ptr = (long *)array;
    int k;

    for(k=1; k <= 10; k++)
    {
        *ptr = Get_DataPointer(); /* you need to dereference ptr to store value */
        ptr += 1; /* increment by one to get to the next address */
    }
}

Print(void* array)
{
    long *ptr = (long *)array;
    int k;

    for(k=0; k < 10; k++)
    {
        long dataPointer = *(ptr + k); /* dereference to read the value */
        printf("Pointer %i, Content=%ld\n", k, dataPointer);
    }
}

Answer 2

您需要更改以上代码

long dataPointer = ((long*)(array+ k));
printf("Pointer %i, Content=%l\n", k, dataPointer);

至

long *dataPointer = (long*)(array+ k);
printf("Pointer %i, Content=%l\n", k, *dataPointer);

这将类型转换（array + k）到长指针（long *）。 * dataPointer将取消引用长指针以打印内容。