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.NET Forum / Languages / Managed C++ / February 2008Template in cpp file?
Hi all, I have a project that contains a templated routine. This same project contains code that tries to construct an instance of that templated routine. I have the following bits and pieces: Something.h // Just the signature, not the implementation template <class T> void MyTemplatedRoutine(T arg); MyTemplatedRoutine.cpp // Implementation template <class T> void MyTemplatedRoutine(T arg) { <implementation> } X.cpp // Try to use it #include "Something.h" int x = 5; a = MyTemplatedRoutine(x); The linker complains that it can't find void __cdecl MyTemplatedRoutine<int>(int). I need to implement the templated routine in a code file rather than in the header file because it contains references to static module-level data declared in the code file. What do I need to do to make the linker happy? TIA - Bob > Hi all, > [quoted text clipped - 16 lines] > int x = 5; > a = MyTemplatedRoutine(x); Your code as shown builds for me fine. I'm suspicious about the assignment to "a" by a function that returns void... Mark  SignatureMark Salsbery Microsoft MVP - Visual C++ > The linker complains that it can't find void __cdecl > MyTemplatedRoutine<int>(int). I need to implement the templated routine [quoted text clipped - 3 lines] > > TIA - Bob > Your code as shown builds for me fine. I'm suspicious about the assignment to > "a" by a function that returns void... Whoops... the assignment to "a" is a typo. In any event, if I have all of the plumbing correct then this should work? I know that exporting templated functions from a DLL is a pain in the you-know-what, so I thought that maybe I was running into a variant of that here. But since everything is in the same project I would expect that C++ is smart enough to wire it all up correctly even if the template implementation is in a code file and not directly incorporated in the referencing code via a header file. I'll stare at my code some more to see if I can figure it out. If I can't then I'll try to simplify it to something as simple as my original posting and I'll follow up with a new and improved post in this NG. > Hi all, > [quoted text clipped - 12 lines] > > X.cpp Argh - I just noticed the 3rd x,cpp file. That won't work since at that point, there's not enough info to create an implemented instance of the template<int> function. Mark SignatureMark Salsbery Microsoft MVP - Visual C++ > // Try to use it > #include "Something.h" [quoted text clipped - 8 lines] > > TIA - Bob > Hi all, > [quoted text clipped - 22 lines] > contains references to static module-level data declared in the code > file. What do I need to do to make the linker happy? Explicitly instantiate the different versions of the template that you need. Something like void MyTemplatedRoutine<int>(int arg); ought to do the trick, or you might need to take its address as in: static void forceInstantiation() { { void (*force)(int) = &MyTemplatedRoutine<int>; } { void (*force)(double) = &MyTemplatedRoutine<double>; } // won't this be prettier with C++0x and type inference! ... } > TIA - Bob Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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