GCC detect 32 or 64 bit system
For example:
#include <iostream>
#if __x86_64__
#define ENV64BIT
#else
#define ENV32BIT
#endif
using namespace std;
int main() {
#ifdef ENV64BIT
cout << "64 bit" << endl;
#endif
#ifdef ENV32BIT
cout << "32 bit" << endl;
#endif
}