Storing C++ template function definitions in a .CPP file


Question

I have some template code that I would prefer to have stored in a CPP file instead of inline in the header. I know this can be done as long as you know which template types will be used. For example:

.h file

class foo
{
public:
    template <typename T>
    void do(const T& t);
};

.cpp file

template <typename T>
void foo::do(const T& t)
{
    // Do something with t
}

template void foo::do<int>(const int&);
template void foo::do<std::string>(const std::string&);

Note the last two lines - the foo::do template function is only used with ints and std::strings, so those definitions mean the app will link.

My question is - is this a nasty hack or will this work with other compilers/linkers? I am only using this code with VS2008 at the moment but will be wanting to port to other environments.

1
461
9/29/2008 3:56:38 PM

Accepted Answer

The problem you describe can be solved by defining the template in the header, or via the approach you describe above.

I recommend reading the following points from the C++ FAQ Lite:

They go into a lot of detail about these (and other) template issues.

209
10/22/2016 1:12:42 AM

For others on this page wondering what the correct syntax is (as did I) for explicit template specialisation (or at least in VS2008), its the following...

In your .h file...

template<typename T>
class foo
{
public:
    void bar(const T &t);
};

And in your .cpp file

template <class T>
void foo<T>::bar(const T &t)
{ }

// Explicit template instantiation
template class foo<int>;

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