Pointer conversion for native 64 application.

Question

Hello,

Below code works fine on 32bit platform but crashed for 64bit platform.

#include <iostream>
#include<string>
#include<Windows.h>
using namespace std;
class CStroageClass
{
    std::string name; 
    int number;
public: 
    CStroageClass(): name("prxy"), number(20)
    {

    }
    void PrintName() { std::cout << "name:" << name << std::endl; }
    void PrintNumber() { std::cout << "number:" << number << std::endl; }
};

int main()
{
    CStroageClass * obj = new CStroageClass;
    cout << obj << std::endl;

    unsigned long  ul = PtrToUlong(obj);

    std::cout << "UL:" << ul << std::endl;

    CStroageClass* so = reinterpret_cast<CStroageClass*>(ULongToPtr(ul));
    cout << so << std::endl;
    so->PrintName();
    so->PrintNumber();

    return 0;
}

How to resolve such error's ?

Answer 1

When you build for 64 bits the PtrToUlong function returns a truncated 32 bit value which cannot be converted back to a valid 64-bit pointer. The source for ULongToPtr contains this warning - "Caution: ULongToPtr() zero-extends the unsigned long value." That is why round-tripping is problematic.

Try this -

    ULONG_PTR  ul = (ULONG_PTR) obj;

    std::cout << "UL:" << ul << std::endl;

    CStroageClass* so = reinterpret_cast<CStroageClass*>(ul);