在长无符号变量中使用指向 select 数字的指针

Question

I am required to add two select only two numbers from a Variable ie 0X11223344 and I want my pointers to pick 22 in the middle of the array. how do I go about it

Answer 1

You can use shift and modulo operations to get the value

int main(){
   return (0X11223344 >> 16) % 256;
}

The program returns 34 == 0x22

A right shift of 4 removes 1 digit. A right shift of 16 removes 4 digits. A modulo of 16 removes all but one digits. A modulo of 16*16= 256 removes all but 2 digits.

You can also get the value with pointer operations:

int main() {
    int endianness = 2;
    int a = 0x11223344;
    char *b = ((char *) &a) + endianness;
    return *b;
}

The value of endianess is implementation defined. On a system with little endiannes it's 2

|01 02 03 04|  memory address
-------------
|44 33 22 11| 4 byte int with address 01 and value 0x11223344
|  |  |22|  | 1 byte char with address 03 and value 0x22

and on a system with big endianness it's 1

|01 02 03 04|  memory address
-------------
|11 22 33 44| 4 byte int with address 01 and value 0x11223344
|  |22|  |  | 1 byte char with address 02 and value 0x22