QTestLib doesn't recognize NULL pointers?

[entonjackson]

Hello, i have a strange issue.

I'm having a testclass in which i tried to make a test fail, by letting an Object Pointer point to NULL and after that, calling a method on that Pointer like this...

HelloWorld *obj = NULL;
obj->hello()
QCOMPARE(obj->hello(), QString("Hello World!"));

HelloWorld *obj = NULL;
obj->hello()
QCOMPARE(obj->hello(), QString("Hello World!"));

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Actually, the above is the code of my first test method.
the strange is, that it never fails... compiler compiles, and after running it, it says always PASSED.

what am i understanding wrong??

[wysota]

That's hardly possible, this code should crash. Show your actual code. If that's the actual code then the only explanation is that it is never ran.

[stampede]

It depends on what you are doing in the hello() method, if you don't access the object's data members, the code can run without a crash. For example, this does not crash (g++ 4.5.2):

#include <iostream>
 
class Test{
public:
    void test(){
        std::cout << "method called\n";
    }
};
 
int main(){
    Test * t = NULL;
    t->test();
    return 0;
}

#include <iostream>

class Test{
public:
    void test(){
        std::cout << "method called\n";
    }
};

int main(){
    Test * t = NULL;
    t->test();
    return 0;
}

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[entonjackson]

Ok, this sounds logical.
I'm accessing nothing class-specific in that method. I'm just returning a new QString Object...

QString HelloWorld::hello()
{
    return "Hello World!";
}

QString HelloWorld::hello()
{
    return "Hello World!";
}

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So... i've just tested it with this:

QString HelloWorld::hello()
{
    _string = "Hello World!";
    return _string;
}

QString HelloWorld::hello()
{
    _string = "Hello World!";
    return _string;
}

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...while _string is a member of HelloWorld class. And now it crashes, like it should!

Wondering if the compiler is optimizing the return "Hello World"; from the first hello() method out, and that is the reason no crash occures.
Or what other reason there is, why there's no error at runtime...?

Thank you!

[wysota]

No crash occurs because the compiler never tries to dereference "this" when inside the hello() method. If you make that method virtual, it will start crashing.

[entonjackson]

Ok!
Thanks a lot!