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[C++] typeof ?

Started by ColeFreeman Mar 3, 2008 at 1:02 PM 3 replies 4.4k views

Original Post

Mar 3, 2008 at 1:02 PM

Hi. I cannot find functionality for deducing compile time type from an arbitrary variable, typeof is removed completely?. (VS2005 unmanaged c++) BOOST_TYPEOF needs registering of user types/templates beforehand, which is not possible in many cases. So what I need to do in compiletime is: AnyType a; typeof(a) b;//AnyType b It will be used together with macros to simplify some heavily templated programming interfaces I have that are quite tedious to use at the moment. Any info is greatly appreciated. Thank you.

Sneftel

Mar 3, 2008 at 1:09 PM

There's nothing in that form you can do. Depending on the context, there may be a different way, involving templates. See, for example, the implementation of std::swap. Disregarding exception safety, it looks something like this:

template<typename T>void swap(T & a, T & b){    T temp = a;    a = b;    b = temp;}int foo = 3;int bar = 4;swap(foo, bar);

Note that "temp" has the same type as "a" and "b".

ToohrVyk

Mar 3, 2008 at 1:12 PM

There is no standard means of obtaining the type of a variable, although there have been proposals to add this to the next standard (C++0x).

The only means you have at your disposal, when manipulating a variable of unknown type, is to place yourself within a context where that type is obvious:

UnknownType a;typeof(a) b; // Obviously does not workfrobnicate(a,b);

Becomes:

template<typename T> impl(T & a){  T b;  frobnicate(a, b);}UnknownType a;impl(a);

CmpDev

Mar 3, 2008 at 2:08 PM

As has been said templates are the key here; yet if you were using g++ then typeof could be used.

ColeFreeman

Mar 3, 2008 at 2:09 PM

Thanks for the quick replies.

Sticking to the global context for a while longer then, thx again.

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