Thread: Specialized template outside-class-definition problem during compile time.

I've done an example of 'template specialization'. Here is the code:

Code:

// template specialization
#include <iostream>

using namespace std;

// class template:
template <class T>
	class mycontainer {
		private:
			T element;
		public:
			// only prototype
			mycontainer (T);
			T increase ();
	};

// class method definition
template <class T>
	mycontainer<T> :: mycontainer(T arg) {
		element = arg;
	}

template <class T>
	T mycontainer<T> :: increase () {
		return ++element;
	}
	
// class template specialization: 
template <> 
	class mycontainer <char> { // specialized for char type
		private:
			char element;
		public:
			mycontainer(char arg) {
				element = arg;
			}
			char uppercase() {
				if ((element >= 'a') && (element <= 'z')) {
					element += 'A'-'a';
					return element;
				}
				return '0';
			}
	};

// 
int main () {
	mycontainer<int> myint (7);
	mycontainer<char> mychar ('j');
	//
	cout << myint.increase() << endl;
	cout << mychar.uppercase() << endl;
	//
	return 0;
}

The compiler compiled this code successfully, but when I try to move the definition of the constructor and the method outside the class, the compiler cannot compile it.

Here is the code with outside-class-definition:

Code:

// template specialization
#include <iostream>

using namespace std;

// class template:
template <class T>
	class mycontainer {
		private:
			T element;
		public:
			// only prototype
			mycontainer (T);
			T increase ();
	};

// class method definition
template <class T>
	mycontainer<T> :: mycontainer(T arg) {
		element = arg;
	}

template <class T>
	T mycontainer<T> :: increase () {
		return ++element;
	}
	
// class template specialization: 
template <> 
	class mycontainer <char> { // specialized for char type
		private:
			char element;
		public:
			// only prototype
			mycontainer(char);
			char uppercase();
	};

// definition
template <>
	mycontainer<char> :: mycontainer(char arg) {
		element = arg;
	}

template <>
	char mycontainer<char> :: uppercase () {
		if ((element >= 'a') && (element <= 'z')) {
			element += 'A'-'a';
			return element;
		}
		return '0';
	}

// 
int main () {
	mycontainer<int> myint (7);
	mycontainer<char> mychar ('j');
	//
	cout << myint.increase() << endl;
	cout << mychar.uppercase() << endl;
	//
	return 0;
}

The compiler generated these errors:

Code:

... error C2910: 'mycontainer<char>::{ctor}' : cannot be explicitly specialized
... error C2910: 'mycontainer<char>::uppercase' : cannot be explicitly specialized

Even when I add the 'char' between the angle, the compiler still gave errors.

Code:

template <char>
	mycontainer<char> :: mycontainer(char arg) {
		element = arg;
	}

template <char>
	char mycontainer<char> :: uppercase () {
		if ((element >= 'a') && (element <= 'z')) {
			element += 'A'-'a';
			return element;
		}
		return '0';
	}

With this code, The compiler generated these errors:

Code:

... error C2244: 'mycontainer<char>::{ctor}' : unable to match function definition to an existing declaration
        definition
        'mycontainer<char>::mycontainer(char)'
        existing declarations
        'mycontainer<char>::mycontainer(const mycontainer<char> &)'
        'mycontainer<char>::mycontainer(char)'
... error C2244: 'mycontainer<char>::uppercase' : unable to match function definition to an existing declaration
        TemplateSpecialization3.cpp(36) : see declaration of mycontainer<char>::uppercase'
        definition
        'char mycontainer<char>::uppercase(void)'
        existing declarations
        'char mycontainer<char>::uppercase(void)'

I use the compiler "Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 15.00.21022.08 for 80x86", and compile the source-code with "cl /clr *.cpp" command.

Did anyone encounter this problem? Why? Is my second code incorrect or the compiler doesn't allow?

Thank you very much

Hi scwizzo, it's just a try-out to learn something more careful. The most effective way to learn something is to try it in all cases.

You are right. It can be compiled, but something is so secret here )

Originally Posted by Elysia

I believe it has to do with the fact that your class template specializes the actual class and its functions. Since it's specialized, it's no longer a template.
Therefore, those functions are like any normal functions, hence you don't need to put the specializing part of it there.
Not 100% sure, however.

It can be a reasonable description about what we'd seen. Maybe it's true.