c++ - Gmock - how to override library function -

i trying override simple cmath library function - 'pow'

below code :

#include "stdafx.h" #include <gmock/gmock.h> #include <gtest/gtest.h> #include <cmath>  class powinterface { public:     virtual ~powinterface() {}     virtual double pow(double _xx, int _yx) = 0; };  class libxmock : public powinterface { public:     virtual ~libxmock() {}     mock_method2(pow, double(double _xx, int _yx)); };  int main() {      libxmock libxmockobj;      expect_call(libxmockobj, pow(10.00, 3));     double ans = libxmockobj.pow(10.00, 3);     expect_eq(2, ans); }    

the code compiles fine execution gives below output:

c:\gmock> _test_example.cpp(36): error:       expected: 2 equal to: ans       is: 0 press key continue . . . 

i unsure why returned value 0 - wondered if need add self definition of 'pow' method injected below code:

double pow(double _xx, int _yx) {     return libxmockobj.pow(_xx , _yx); } 

now compiler fails compile code stating re-definition of pow method - hence how can implement own pow library method , call it?

i did not try compile, idea that:

#include "stdafx.h" #include <gmock/gmock.h> #include <gtest/gtest.h> #include <cmath>  class powinterface { public:     virtual ~powinterface() {}     virtual double pow(double _xx, int _yx) = 0; };  class libxmock : public powinterface { public:     virtual ~libxmock() {}     mock_method2(pow, double(double _xx, int _yx));     double custompow(double _xx, int _yx) {         return 2;     } };  int main() {      libxmock libxmockobj;      expect_call(libxmockobj, pow(10.00, 3)).times(1).willonce(::testing::invoke(libxmockobj, &libxmock::custompow));     double ans = libxmockobj.pow(10.00, 3);     expect_eq(2, ans); }