Template functions and Visual C++ 2008

[Andreas5]

Hello again, i ran into some trouble with Visual C++ 2008 when i tried to use a template function. I only get this error when i try to use the function from main().

I used another template function succesfully earlier, but i can not figure out what is wrong with this one.

Any help is appreciated.:)

This is the error message i receive :P

error LNK2019: unresolved external symbol "void __cdecl split2<class std::back_insert_iterator<class std::list<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::allocator<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > > > > >(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > const &,class std::back_insert_iterator<class std::list<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::allocator<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > > > >)" (??$split2@V?$back_insert_iterator@V?$list@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@@std@@@@YAXABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V?$back_insert_iterator@V?$list@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V?$allocator@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@2@@std@@@1@@Z) referenced in function _main

This is part of my *.h file:

template <class Out>
void split2(const std::string&, Out);

And this is is part of my *.cpp file:

template <class Out>
void split2(const string& str, Out os) {

	typedef string::const_iterator iter;
	iter i = str.begin();
	while (i != str.end()) {

		// ignore leading blanks
		i = find_if(i, str.end(), not_space);

		// find end of next word
		iter j = find_if(i, str.end(), space);

		// copy the characters in [i, j)
		if (i != str.end())
			*os++ = string(i, j); // changed
		i = j;
	}
}

Edit: This is an example of how i want to use it in main():

string s;
	while (getline(cin, s))
		split2(s, ostream_iterator<string>(cout, "\n"));

[dusktreader]

The problem is (most likely) that you have to define a template function in the same file where it is declared. For a good over-view and specifics on the multi-file problem, see this.

So, you need to move your implementation of the split2 function to your header file. I know this will be ugly, but it's the only way to make it work well. You'll notice that many projects that use temlate classes and functions make use of a .hpp extension for header files with template implementations. This gives an indication that the header will contain both function declarations and definitions.

[Andreas5]

Aha, that was why. Thank you very much

[jonsca]

Another excellent reference is http://www.parashift.com/c++-faq-lite/templates.html#faq-35.13 (it has a ton of info on template classes too).