Double free in Google Mock

Question

I'm a newbie in Google Test and Mock framework.

I just try to run "Turtle" example, it was successful.

However, error message was displayed : double free or corruption (!prev).

MockTurtle.h

#include <gmock/gmock.h>

class MockTurtle : class Turtle {
    MOCK_METHOD0(PenUp, void());
    MOCK_METHOD0(PenDown, void());
    MOCK_METHOD1(Forward, void(int distance));
    MOCK_METHOD1(Turn, void(int degrees));
    MOCK_METHOD2(GoTo, void(int x, int y));
    MOCK_CONST_METHOD0(GetX, int());
    MOCK_CONST_METHOD0(GetY, int());
};    

Turtle.h

class Turtle {
    virtual ~Turtle() {}
    virtual void PenUp() = 0;
    virtual void PenDown() = 0;
    virtual void Forward(int distance) = 0;
    virtual void Turn(int degrees) = 0;
    virtual void GoTo(int x, int y) = 0;
    virtual int GetX() const = 0;
    virtual int GetY() const = 0;
};    

Painter.h

class Painter    
{
       Turtle* turtle;
public:
       Painter( Turtle* turtle )
               :       turtle(turtle){}

       bool DrawCircle(int, int, int){
               turtle->PenDown();
               return true;
       }
};    

Main_test.cpp

#include <gtest/gtest.h>
#include <gmock/gmock.h>
#include "Painter.h"
#include "MockTurtle.h"

using ::testing::AtLeast;

TEST(PainterTest, CanDrawSomething) {
 MockTurtle turtle;
 EXPECT_CALL(turtle, PenDown())
     .Times(AtLeast(1));

 Painter painter(&turtle);

 EXPECT_TRUE(painter.DrawCircle(0, 0, 10));
}

int main(int argc, char** argv) {
 // The following line must be executed to initialize Google Mock
 // (and Google Test) before running the tests.
 ::testing::InitGoogleMock(&argc, argv);
 return RUN_ALL_TESTS();
}    

Result

[==========] Running 1 test from 1 test case.    
[----------] Global test environment set-up.
[----------] 1 test from PainterTest
[ RUN      ] PainterTest.CanDrawSomething
[       OK ] PainterTest.CanDrawSomething (0 ms)
[----------] 1 test from PainterTest (0 ms total)
[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1 ms total)
[  PASSED  ] 1 test.
*** Error in `/home/user/workspace/google_mock_2/Debug/google_mock_2': double free or corruption (!prev): 0x098a8080 ***

I tried to google, saw several same problems. People said that should not use mock as global variable.

But my example did not use global variable.

Please help me explain why double free happen. Thanks in advance!

Answer 1

Last time, I built google test and google mock in SHARED library. And error (double free) happened.

I have tried to build as STATIC library. This error no longer appear. I don't know why but I will investigate to know more detail.

Answer 2

I had the same issue. In my case, the problem was to be linking both google test and google mock. I solved the problem by just linking gmock, no gtest.

I think this occurs because, as far as I understand, gmock already links statically gtest: When you compile gmock as a dynamic library, gtest is generated as well (as a static library) in the same folder where gmock is built. I suppose gmock depends on, and uses, this library.

I suppose that, in some way, linking gtest twice (both statically and dynamically), produces a free() to be executed twice.