Significant difference? C++ Templates

sam · April 14th, 2003, 10:15 pm

Hi all, Just a query that I've come up with regarding the declaration of Templates.... What is the difference (is there?) between the following template declarations?template<class T> class Test{...};template<typename T>class Test{...};As far as I can tell from some simple programs the only difference is that the first is used for the standard types used in C++, e.g. int, double, char... and the latter is used for user specified classes that C++ would not know about normally. But is there anything else subtle happening here?Many Thanks!Sam

afoster · April 15th, 2003, 6:34 am

The typename and class keywords are completely interchangable and the preference to use one or the other is simply a matter of style (see Bjarne Stroustrup The C++ Programming Language, 3rd Edition)

sam · April 15th, 2003, 10:41 am

Thanks.

Mukuzani · April 15th, 2003, 1:53 pm

QuoteOriginally posted by: afosterThe typename and class keywords are completely interchangable and the preference to use one or the other is simply a matter of style (see Bjarne Stroustrup The C++ Programming Language, 3rd Edition)They are the same in sam's example, but could be different in different context. Scott Meyers in "effective STL" gives an example of dependent types (p. 8)template<typename C>bool f(C& c){typename C::iterator it;//should be typename........................................

sam · May 4th, 2003, 7:21 pm

I've recently come across the following definition for a template:template<typename T, size_t size>I'm ok with the first term in the brackets, but have never seen the second term's declaration type. Is it some special version of 'typename' or 'class' that only allows numerical objects?Thanks,Sam

mj · May 4th, 2003, 7:49 pm

the second template argument can only be a number in this case.MJ

Patrik · May 4th, 2003, 8:55 pm

All the OS'es I have looked at has size_t as a typedef to an integer type of some kind/size.You can safely look at it as a integer until you really need to know more - then consult theheaderfiles for your OS/compiler.

sam · May 5th, 2003, 2:43 pm

Thanks for the responses. Much appreciated.Sam

Cuchulainn · January 29th, 2015, 11:32 am

From quantnet.com

dd3 · January 29th, 2015, 5:00 pm

QuoteOriginally posted by: samI've recently come across the following definition for a template:template<typename T, size_t size>I'm ok with the first term in the brackets, but have never seen the second term's declaration type. Is it some special version of 'typename' or 'class' that only allows numerical objects?Thanks,SamThe second template parameter is used to let the programmer specify a compile-time constant.The most obvious use of this would be for std::array<T, N> where N is the number of elements in the array.

Cuchulainn · January 30th, 2015, 10:39 am

Another example is traits and policy-based design