CODEWITHSUNDEEP
c++templatesboostc++03
ScaryAardvark
ScaryAardvark

Reputation: 2965

prevent template instantiation when template argument is zero

I have a templated class

template< std::size_t Size >
class Buffer
{
....
};

I'd like to prevent instantiation of this template when the Size argument is zero. i.e. generate a compiler warning for the following.

Buffer< 0 > buf;

but all other variants would work.

Buffer< 10 > buf;

I'm looking at using boost::enable_if_c but I don't understand how to get it working.

--Update-- I can't use any c++11 features, unfortunately

Upvotes: 4

Views: 282

Answers (5)

David G
David G

Reputation: 96835

std::enable_if

template <std::size_t N, typename = typename std::enable_if<!!N>::type>
class Matrix {};

static_assert:

template <std::size_t N>
class Matrix
{
    static_assert(N, "Error: N is 0");
};

Upvotes: 0

Nobody moving away from SE
Nobody moving away from SE

Reputation: 9547

Simply specialize the template to a state that cannot be instatiated:

template <>
class Buffer<0>;

That way the class cannot be constructed. Usage will result in: error: aggregate ‘Buffer<0> buf’ has incomplete type and cannot be defined

Upvotes: 10

Some programmer dude
Some programmer dude

Reputation: 409356

If your compiler support it, try static_assert:

template< std::size_t Size >
class Buffer
{
    static_assert(Size != 0, "Size must be non-zero");

    // ...
};

Upvotes: 6

Yuushi
Yuushi

Reputation: 26060

Utilizing BOOST_STATIC_ASSERT might be even easier:

#include <boost/static_assert.hpp>

template< std::size_t Size >
class Buffer
{
    BOOST_STATIC_ASSERT(Size != 0);
};


int main()
{
    Buffer<0> b; //Won't compile
    return 0;
}

Upvotes: 9

Cheers and hth. - Alf
Cheers and hth. - Alf

Reputation: 145359

#include <stddef.h>

typedef ptrdiff_t Size;

template< Size size >
class Buffer
{
    static_assert( size > 0, "" );
};

int main()
{
#ifdef  ZERO
    Buffer<0>   buf;
#else
    Buffer<1>   buf;
#endif
}

Upvotes: 1

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