Example of struct initialization via memcpy and using a union.

InitByBuffer.cpp

#include <iostream>
#include <cstdio>
#include <cstdlib>

using namespace std;

class Pair
{
    public:
        int x;
        int y;
        
        void print()
        {
            cout << "(" << x << ", " << y << ")" << endl;
        }
};


union PairBuffer
{
    Pair p;
    char buffer[8];
    int ibuffer[2];
};


void testUnion()
{
    cout << endl;
    cout << "Testing initializations using a union" << endl;
    
    PairBuffer pb;
    pb.p.x = 1;
    pb.p.y = 10;
    
    printf("%x%x%x%x.%x%x%x%x\n", 
        pb.buffer[0], pb.buffer[1], pb.buffer[2], pb.buffer[3], 
        pb.buffer[4], pb.buffer[5], pb.buffer[6], pb.buffer[7]
    );
    printf("%x.%x", pb.ibuffer[0], pb.ibuffer[1]);
}


void testMemcpy()
{
    cout << endl;
    cout << "Testing initialization using memcpy" << endl;
    
    char buffer[8];
    int a = 4;
    int b = 7;
    memcpy(buffer, &a, 4);
    memcpy(buffer + 4, &b, 4);
    printf("(%i, %i)\n", (int)*buffer, (int)*(buffer+4));
    
    Pair p;
    p.x = 1111;
    p.y = 2222;
    p.print();
    memcpy(&p, buffer, 8);
    p.print();
}


int main()
{
    testMemcpy();
    testUnion();
    return 0;
}