有人可以解释为什么这会出现SEG故障(C编程)

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，我使用的示例地址为0x00400002，只是此功能不断给我带来SEG错误，不太明白为什么，因为所涉及的数组的大小为1000。谢谢。

Answer 1

您的第一个开关看起来很奇怪，只有0、1和7处理。并且在每种情况的结尾都没有break;语句。

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是0x00400002，因此switch将从case 0开始执行而且您在每个case X中都没有任何break，所有代码将运行。也就是说，终于index等于address - START_STACK_ADDRESS。

也许这是原因。

尝试在 case s之间添加 break s。

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;
}