类型转换

代码如下

int main(int argc, const char * argv[]) {
    int a = 0xABCD07; // 0000 0111 最低位的一个字节
    int b = 0xABCD77; // 0111 0111
    int c = 0xABCD87; // 1000 0111
    int d = 0xABCDF7; // 1111 0111
    
    char *a1 = (char*)&a;
    unsigned char *a2 = (unsigned char*)&a;
    
    char *b1 = (char*)&b;
    unsigned char *b2 = (unsigned char*)&b;
    
    char *c1 = (char*)&c;
    unsigned char *c2 = (unsigned char*)&c;
    
    char *d1 = (char*)&d;
    unsigned char *d2 = (unsigned char*)&d;
    
    printf("%08x, %08x\n", *a1, *a2); //注意char*转换时符号位扩展
    printf("%08x, %08x\n", *b1, *b2);
    printf("%08x, %08x\n", *c1, *c2);
    printf("%08x, %08x\n", *d1, *d2);
    
    return 0;
}

运行结果

运行结果

注意char* 和 unsigned char*的打印结果的不同

对于一个char类型的变量来说，最高位是符号位，低7位才是数据位，所以，对于上边的c和d，最低一字节的第八位是1，所以对于printf用%08x的时候，c1和d1会对最高位的符号位1做符号位扩展，所以打印出来的会是fffffff7.