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rsnd	Jul 4th, 2007 1:38 PM

C++ template classes question

#include <stdio.h>

#include <memory>

template <class _Type, int _MinLen = 32, _Type _DefValue = 0>

class dlist {

public:

        _Type * items;        

        int length;

};

dlist<char*> motd_lines;

int main (){

    return 0;

}

H:\test.cpp:9: error: could not convert template argument `0' to `char*'

H:\test.cpp:9: error: invalid type in declaration before ';' token

Using the latest version of Dev-Cpp and whatever Mingw that came with it. My question is...what am I doing wrong here? It compiles perfectly with both VC++ 6 and 2005.

pegasus001

Jul 4th, 2007 1:41 PM

Replace the stdio with cstdio.

rsnd	Jul 4th, 2007 1:47 PM

umm ok...what was the problem?

pegasus001

Jul 4th, 2007 1:48 PM

All the C header files in C++ have a c letter before them.

rsnd	Jul 4th, 2007 2:05 PM

Well my project didn't compile in Dev-Cpp so I extracted that bit. But it sill doesn't compile. How about this?

#include <cstdio>

#include <memory>

template <class _Type, int _MinLen = 32, _Type _DevValue = 0>

class dlist {

public:

        _Type * items;        

        int length;

        _Type get(int i){

                return (i >= 0 && i < length)? items[i] : _DevValue ;

        }

};

dlist<char*> motd_lines;

int main (){

    return 0;

}

Quote:

H:\test.cpp:12: error: could not convert template argument `0' to `char*'
H:\test.cpp:12: error: invalid type in declaration before ';' token

seems like some sort of type casting failure but isnot 0 a valid value for a pointer?

Cache

Jul 4th, 2007 2:34 PM

I think pointer template arguments have to have external linkage. Presumably '0' doesn't. You'll have to do some digging.

rsnd	Jul 4th, 2007 2:48 PM

Well, "dlist<int,32,5> motd_lines;" would work just fine. I'm removed the "_DevValue" parameter and it compiled just fine. Thanks everyone.

The Dark

Jul 4th, 2007 6:42 PM

You could try using a cast to _Type around the 0 in the initialiser.

Cache

Jul 4th, 2007 7:18 PM

Quote:

Originally Posted by The Dark (Post 130032)

You could try using a cast to _Type around the 0 in the initialiser.

It still wouldn't have external linkage.

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