Re: Problem with template

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Mon, 07 May 2007 18:28:24 +0200

Message-ID:

<5a929iF2m9erpU1@mid.individual.net>

* desktop:

When I try to compile this template I get an error in the line:

"enum { Yes = sizeof(IsClassT<T>::test<T>(0)) == 1};"

saying:

blop.hpp:8: error: expected primary-expression before ?>? token

#ifndef BLOP_HPP_
#define BLOP_HPP_

template<typename T>
class IsClassT {
    public:
        enum { Yes = sizeof(IsClassT<T>::test<T>(0)) == 1};
        enum { No = !Yes};
        //int getInt(){return a;};

    private:
        typedef char One;
        typedef struct { char a[2];} Two;
        template<typename C> static One test(int C::*);
        template<typename C> static Two test();
        static const int a = 10;

};

Any ideas why I get this error?

One reason is that it's not known at that point that "test" is a
template. You could fix that by inserting the word "template", but
there are other problems. Try

template< typename T >
class IsClassT
{
private:
     typedef char One;
     typedef struct { char a[2];} Two;
     template<typename C> static One test(int C::*);
     template<typename C> static Two test(...);
public:
     enum { yes = sizeof(test<T>(0)) == 1};
     enum { no = !yes};
};

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?