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
}
 
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