Are default function parameters in allowed in function templates?

[BRG]

I know that default template arguments cannot be used in function
templates but are default function parameters legal?

That is, is this:
----------------------------------
#include <functional>

template<class T, class C> bool count(T x[], C cmp = std::less<T>())
{
for(int i = 0; i < 9; ++i)
if(cmp([i], x[i + 1]))
return true;
return false;
}
----------------------------------
legal C++ code?

count(x, std::less<int>( )); // compiles ok, but
count(x); // gives "could not deduce template argument for 'C'"

Brian Gladman

[Ulrich Achleitner]

On Tue, 04 Jan 2005 13:06:28 +0000, BRG <br*@nowhere.or g> wrote:

>> template<class T, class C> bool count(T x[], C cmp = std::less<T>())

this is never a correct place for a default _type_. in a function's
parameter list there can only be default _values_.

Yes, but std::less<T> and std::less<T>() are values, not types, aren't
they?

the former is a type, the latter is a value / object. sorry, i overlooked
the () in your original posting...

[BRG]

Ulrich Achleitner wrote:

On Tue, 04 Jan 2005 13:06:28 +0000, BRG <br*@nowhere.or g> wrote:

>>> template<class T, class C> bool count(T x[], C cmp = std::less<T>())

this is never a correct place for a default _type_. in a
function's parameter list there can only be default _values_.

Yes, but std::less<T> and std::less<T>() are values, not types,
aren't they?

the former is a type, the latter is a value / object. sorry, i
overlooked the () in your original posting...

Thanks for taking an interest in this.

I have had to abandon defaults here as I cannot find a way of making
them work. What has worked as a way of inling the comparison code (to
avoid the overhead of a function call) is:

template<class T> inline bool
lt_f(const T& x, const T& y) { return x < y; }

template<class T, bool C(const T&, const T&)>
bool count(T x[]) { ... C(x[j], x[i]) ... }

...
int q[10];
count<int, lt_f<int> >(q);
...

But I have had to build my own comparison templates in place of those in
<functional>.

Thanks again for your input.

Brian Gladman