Try to access the private property of another object of the same class.

private-access.cpp

#include <cstdio>

class Test {
  private:
    int foo;

  public:
    Test(int foo_value) {
      foo = foo_value;
    }
    int getFoo(Test* other) {
      return other->foo;
    }
};

int main() {
  Test* a = new Test(5);
  Test* b = new Test(10);

  printf("%i\n", a->getFoo(b));

  return 0;
}