Re: Template trouble

• Subject: Re: Template trouble
• From: Glen Low <email@hidden>
• Date: Wed, 30 Aug 2006 09:04:13 +0800
• Delivered-to: email@hidden
• Delivered-to: email@hidden

Edward:

On 29/08/2006, at 12:09 PM, Edward K. Chew wrote:

First of all, thanks for the various replies!

So, after another day of pounding on it, I was able to condense the specialization problem down to a simple example:

//__________________________________________________

#include <cstring>
#include <iostream>

namespace AccessFunctions
{
	template<typename T> int dataLength(T value)
	{
		return sizeof value;
	}

	template<typename T> int dataLength(T* value)
	{
		return sizeof(T);
	}

	template<> int dataLength(const char* str)
	{
		return std::strlen(str);
	}
}

template<typename T>
class TAccessClass
{
public:
	static int dataLength(T value)
	{
		return AccessFunctions::dataLength<T>(value);
	}
};

int main (int argc, char * const argv[]) {
	using namespace std;
	const char str[] = "Hello, world!";
	
	cout << "Case 1: ";
	cout << AccessFunctions::dataLength(str);
	cout << endl;
	
	cout << "Case 2: ";
	cout << TAccessClass<const char*>::dataLength(str);
	cout << endl;
	
	return 0;
}

Let's analyze what happens in Case 2:

TAccessClass <const char*>::dataLength (str);

is a call to

template<> int dataLength <const char*> (const char* str)
	{
		return std::strlen(str);
	}

// these are classes therefore are partially specialized

template <typename T> struct dataLength_helper
	{
		static int getsize (T value) { return sizeof (value); }
	};

template <typename T> struct dataLength_helper <T*>
	{
		static int getsize (T* value) { return sizeof (T); }
	};

template <> struct dataLength_helper <const char*>
	{
		static int getsize (const char* value) { return std::strlen (value); }
	};

// call over to the partially specialized helper
template <typename T> int dataLength (T value)
{
	return dataLength_helper <T>::getsize (value);
}

Cheers, Glen Low

---
pixelglow software | simply brilliant stuff
www.pixelglow.com
aim: pixglen

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