Question

int load_byte(int memory[],int address) {
//This function works by finding the appropriate word then masking
//to obtain the relevant byte
int index,section;

    switch (address>>28) {
        case 0:
            index = address - START_ADDRESS;
            printf("index = %d",index);
        case 1:
            index = address - START_DATA_ADDRESS;
        case 7:
            index = address - START_STACK_ADDRESS;
   }

    section = index%4;
    index = index/4;
    switch (section) {
    case 0:
        return memory[index]&0x000000ff;
    case 1:
        return (memory[index]&0x0000ff00)>>8;
    case 2:
        return (memory[index]&0x00ff0000)>>16;
    case 3:
        return (memory[index]&0xff000000)>>24;
    }

}

START_ADDRESS的值为0x00400000，我使用的样本地址是0x00400002，只是这个函数不断给我一个seg错误，不太明白为什么有问题的数组大小为1000.提前感谢

Answer 1

你的第一个开关看起来很奇怪，只处理0,1和7。每个案例结尾都没有break;个陈述。

Answer 2

代码：

switch (address>>28) {
    case 0:
        index = address - START_ADDRESS;
        printf("index = %d",index);
    case 1:
        index = address - START_DATA_ADDRESS;
    case 7:
        index = address - START_STACK_ADDRESS;
    }

由于address为0x00400002，因此switch将从case 0开始执行，并且您在每个break中都没有case X，所有代码都将运行。也就是说，最后index将等于address - START_STACK_ADDRESS。

也许这就是原因。

尝试在break s之间添加case。

switch (address>>28) {
    case 0:
        index = address - START_ADDRESS;
        printf("index = %d",index);
        break;
    case 1:
        index = address - START_DATA_ADDRESS;
        break;
    case 7:
        index = address - START_STACK_ADDRESS;
}

有人可以解释为什么会出现seg故障（C编程）吗？

2 个答案: