Union LARGE_INTEGER

November 4, 2022

This code is from MSDN. So, we have an union, which contains the struct and the variable. In my code I declared the prototype of union and then initialized the "QuadPart" of union. But printing the Quad Part doesn’t give the full number but the LowPart of it. Is it a way it should be?

typedef union _LARGE_INTEGER
{
        struct {
                unsigned LowPart;
                unsigned HighPart;
        } u;
        unsigned long long QuadPart;
} LARGE_INTEGER;


int main(int argc, char** argv){
        LARGE_INTEGER num1;
        num1.QuadPart = 0x1020304050607080;
        printf("Low: %x, high: %x, quad: %x\n", num1.u.LowPart, num1.u.HighPart, num1.QuadPart);


        return 0;
}

I expected the full number displayed by num1.QuadPart

>Solution :

use llx for printing long long type printing in hex format

#include <stdio.h>

typedef union _LARGE_INTEGER
{
        struct {
                unsigned LowPart;
                unsigned HighPart;
        } u;
        unsigned long long QuadPart;
} LARGE_INTEGER;


int main(int argc, char** argv){
        LARGE_INTEGER num1;
        num1.QuadPart = 0x1020304050607080;
        printf("Low: %x, high: %x, quad: %llx\n", num1.u.LowPart, num1.u.HighPart, num1.QuadPart);


        return 0;
}