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.

Answer 1

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:

• Why can’t I separate the definition of my templates class from its declaration and put it inside a .cpp file?
• How can I avoid linker errors with my template functions?
• How does the C++ keyword export help with template linker errors?

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