Programming Forums > Application Development > C++

earl · Jun 20th, 2005, 1:56 PM

Is it possible to have a nontype default template parameter that is not an int or a pointer? Every example I see uses the integer example to initialize something like a Stack or Queue template.

For instance, is it possible to specify a nontype template parameter that is a struct? I was trying this but getting errors indicating that the struct wasn't a valid as a non-type parameter, but I'm not sure if that's a language restriction or requires compiler flags...? Thanks.

Animatronic · Jun 20th, 2005, 2:12 PM

Something like this:

(Toggle Plain Text)

struct Foo
{
};

template<class _Ty = Foo>
struct Bar
{
};

works fine.

uman · Jun 20th, 2005, 5:02 PM

I think he means

template<std::string whatever = std::string("foo")>
struct zooglemcdorfnick
{
//w/e
};

I'm not sure if you can do that, I don't use templates a lot.

earl · Jun 20th, 2005, 6:48 PM

uman is correct. I understand how type parameters work, along with template specializations, etc.

But you can also do something like this:

(Toggle Plain Text)

template<class T, int size = 10>
class Stack 
{
  ...
  T array[size];
  ...
};

But I'm wondering if it's possible to do something like this:

(Toggle Plain Text)

template<class T, Obj o = x>
class Foo
{
};

where Obj is some user-defined type and x is an instance. I guess you can't, but you can use pointers/references, i.e.

(Toggle Plain Text)

template<class T, Obj *o>
class Foo
{
};

But actually I'm not sure if you can specify default parameters for pointer/reference parameters...

Eggbert · Jun 21st, 2005, 11:27 AM

>Is it possible to have a nontype default template parameter that is not an int or a pointer?
Your choices for non-type template parameters are limited to an integral or enum type, a pointer to object or function, a reference to object or function, and a pointer to a member. All of them allow default arguments.

Jun 20th, 2005, 1:56 PM	#1
earl Newbie Join Date: Jun 2005 Posts: 18 Rep Power: 0	nontype default template parameters Is it possible to have a nontype default template parameter that is not an int or a pointer? Every example I see uses the integer example to initialize something like a Stack or Queue template. For instance, is it possible to specify a nontype template parameter that is a struct? I was trying this but getting errors indicating that the struct wasn't a valid as a non-type parameter, but I'm not sure if that's a language restriction or requires compiler flags...? Thanks.

Jun 20th, 2005, 2:12 PM	#2
Animatronic Programmer Join Date: Jun 2005 Posts: 99 Rep Power: 4	Something like this: (Toggle Plain Text) struct Foo { }; template<class _Ty = Foo> struct Bar { }; struct Foo { }; template<class _Ty = Foo> struct Bar { }; works fine.

Jun 20th, 2005, 6:48 PM	#4
earl Newbie Join Date: Jun 2005 Posts: 18 Rep Power: 0	uman is correct. I understand how type parameters work, along with template specializations, etc. But you can also do something like this: (Toggle Plain Text) template<class T, int size = 10> class Stack { ... T array[size]; ... }; template<class T, int size = 10> class Stack { ... T array[size]; ... }; But I'm wondering if it's possible to do something like this: (Toggle Plain Text) template<class T, Obj o = x> class Foo { }; template<class T, Obj o = x> class Foo { }; where Obj is some user-defined type and x is an instance. I guess you can't, but you can use pointers/references, i.e. (Toggle Plain Text) template<class T, Obj o> class Foo { }; template<class T, Obj o> class Foo { }; But actually I'm not sure if you can specify default parameters for pointer/reference parameters...

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Jun 20th, 2005, 5:02 PM	#3
uman Expert Programmer Join Date: Dec 2004 Posts: 794 Rep Power: 4	I think he means template<std::string whatever = std::string("foo")> struct zooglemcdorfnick { //w/e }; I'm not sure if you can do that, I don't use templates a lot.

Jun 21st, 2005, 11:27 AM	#5
Eggbert Professional Programmer Join Date: Nov 2004 Posts: 250 Rep Power: 4	>Is it possible to have a nontype default template parameter that is not an int or a pointer? Your choices for non-type template parameters are limited to an integral or enum type, a pointer to object or function, a reference to object or function, and a pointer to a member. All of them allow default arguments.

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Programming Forums > Application Development > C++

nontype default template parameters