C++Talk.NET

yyf · Guest

Hi,everyone. I have a question about non-type template-parameter:

According to the standard, non-type template-parameter can be of
type "pointer to function", so the following template definitions:

template< class T, int(*func)(int) >
class Template1
{
// ...
};

template< class T, T(*func)(T) >
class Template1
{
// ...
};

should be leagal, right?
If the answer is yes, then which compiler(s) can handle that?
My VC6.0 at hand won't accept them :(

Thx!

[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

Alex Beluga · Guest

Probably because VC6 as usually wan't support standart well Sad

g++ and VC7.1 compiled all right.
As I can understand, you can pass these pointers to constructor.

[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

Ralph Zhang · Guest

It's surely legal Smile

We all know that VC6 is not a good example for standard conformancy.
It compiles very well in VC7.1.

[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

pmdoc · Guest

Re: legality of pointer to function as non-type parameter

The standard limits non-type parameters to constant 'integral'
expressions
known at compile-time which includes the addresses of global objects
such as
functions.

So unfortunately floating point values are not legal and neither are
string
literals (although for good reasons).

Anyone serious about template programming should buy a copy of 'C++
Templates: the complete guide' by Josuttis and Vandevoorde in which all
these kinds of questions are answered.

---PMD

"Ralph Zhang" <ralph.zhang79 (AT) gmail (DOT) com> wrote