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I am trying to make a framework in C++ using Visual Studio 2010 where I can create objects at the same time as class definition of lots of derived classes. I have been reading a bit on this, and understand the the factory pattern can be used. I however do not manage to get it working.

I have the following code:

#include <stdio.h>
#include <iostream>
#include <vector>

class TestCase;

std::vector<TestCase*> testcases;

class base
{
public:
    static void init();
};

template<class T>
class TestcaseFactory// : public base
{
public:
    TestcaseFactory()
    {
        testcases.push_back(new T());
    }
private:
};


class TestCase
{
public:
    virtual void id() = 0;
};

#define TESTCASE(derived)\
class derived; \
TestcaseFactory<derived> testcase_##derived(); \
class derived : public TestCase

TESTCASE(derived1)
{
    void id() {std::cout << "derived 1" << std::endl;}
};

TESTCASE(derived2)
{
    void id() {std::cout << "derived 2" << std::endl;}
};

int main()
{
    for(unsigned int i = 0; i < testcases.size(); ++i)
    {
        std::cout << i << std::endl;
        testcases[i]->id();
    }
    getchar( );
}

and would have expected the loop in main() to call the two created objects and print

derived1
derived2

However nothing happens. For some reason the code in the #define is never reached. I can not figure out why?

Rajnish
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Robert
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1 Answers1

1
TestcaseFactory<derived> testcase_##derived();

This line declares a function, not a variable. It's a variant of the (most) vexing parse of C++ - if it can be a declaration, it is.

Community
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Bo Persson
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