Static member initialization with class template

Hello,

currently i experience something that i don't understand.

Suppose i have a class

Code:

---


#include <string>

template<typename T>
class ContainerClass
{
public:
    static T doSomething(T a, T b)
    {
        std::string name = ContainerClass<T>::someString;
        return doSomethingAgain(name, T);
    }

    static std::string someString;
};

---

All of this is in a header file. What i now did was to initialize the static member someString in my main.cpp file like:

Code:

---

std::string ContainerClass<float>::someString = std::string("test");
std::string ContainerClass<double>::someString = std::string("test");

---

I use VS2008. When compiling under Debug someString is set correctly, but when compiling for Release the someString doesn't seem to be set at all.

How can this happen?

Best regards, threahdead

someString is one thing, and you are explicitly specifying its definition twice.

try

Code:

---

template< typename T > std::string ContainerClass< T >::someString = std::string("test");

---

if you use a template other than those specified, the someString var should be undefined.

SomeString is being specialized. And since SomeContainer<float> is different from SomeContainer<double>, this is valid C++.
What is not valid, however, is that it should be:

Code:

---

template<> std::string ContainerClass<float>::someString = std::string("test");
template<> std::string ContainerClass<double>::someString = std::string("test");

---

Don't forget the beginning part to tell the compiler it's a specialization!
This prints fine in both release and debug. If you try to use SomeContainer<T> where T is neither float nor double, you WILL get a linking error, however.

Thanks for your replies!
I really didn't intend to specialize the template, and honestly i didn't event know i was doing it :).

I'll try to compile the code with the <T> parameter tomorrow.

Best regards, threahdead

Quote:

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Originally Posted by threahdead

I really didn't intend to specialize the template, and honestly i didn't event know i was doing it :).

---

In order to initialise static members of a template class, it is necessary to specialise the template. In your case, that is because each ContainerClass<T> has a different member named someString (for example, T may be float, or char, or foo, or ...) and each has to be defined once.

Quote:

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Originally Posted by grumpy

In order to initialise static members of a template class, it is necessary to specialise the template. In your case, that is because each ContainerClass<T> has a different member named someString (for example, T may be float, or char, or foo, or ...) and each has to be defined once.

---

But is

Code:

---

template< typename T > std::string ContainerClass< T >::someString = std::string("test");

---

a specialization then? Because the <T> doesn't even specify a certain type.

No, not a specialization. Specializations look exactly the way you were shown by Elysia.