CODEWITHSUNDEEP
c++templatespointers
j4x
j4x

Reputation: 3716

C++: How to prevent template to specialize a pointer?

I start apologising if I am stupid enough to not find the answer if it is so obvious.

I have seen dozens of pages talking about having specific template specialization for pointer parameters.

I'd like to be able, though, of preventing a template to specialize pointer parameters, but I can't figure out how to do this.

template< class T >
void function( T arg )
{
  //...
}

int main( )
{
    int i = 42;

    function( i );    // Ok
    function( &i );   // Die bastart with a compiler error!
}

Is it possible?

Thanks.

Upvotes: 9

Views: 2900

Answers (3)

Christian Rau
Christian Rau

Reputation: 45948

I'm myself a template metaprogramming rookie, but I think

template<typename T>
void function(typename std::enable_if<!std::is_pointer<T>::value,T>::type arg)
{
    //...
}

should work, as this function should only exist for non-pointer parameters. Of course this requires C++11 or at least TR1 or boost's type traits facilities.

Upvotes: 7

user1203803
user1203803

Reputation:

In C++11, you can use static_assert in a way like this:

template<class T>
void func(T arg) {
  static_assert(!std::is_pointer<T>::value,
                "The argument to func must not be a pointer.");
  // Do something after the static_assert.
  // Now you are sure that T isn't a pointer.
}

An example can be found here on Ideone.

I recommend this because it will give more useful error messages when somebody tries to call your function with a pointer (linker errors can be very confusing in this case). Also, linker errors will not show up before linkage occurs.

Upvotes: 14

Armen Tsirunyan
Armen Tsirunyan

Reputation: 133082

You can declare the specialization(in this case it's technically just an overload) but not define it :)

template<typename T >
void function( T arg )
{
//...
}

template<typename T >
void function( T* arg ); //no definition

int main()
{
    int i = 42;
    function( i );    // Ok
    function( &i );   //ERROR
}

Upvotes: 15

Related Questions