Here is an example. I get an error on typename T::SubType*
inside of the template but not outside.
using gcc0x i get
prog.cpp: In instantiation of 'TemplateBase<A>':
prog.cpp:8:36: instantiated from here
prog.cpp:4:22: error: invalid use of incomplete type 'class A'
prog.cpp:8:7: error: forward declaration of 'class A'
in vs i get some random error msg. Here is the code.
template< typename T >
struct TemplateBase {
void ff() {}
typename T::SubType*f(){ return 0; }
//typename T::SubType*f();
};
class A : public TemplateBase< A > {
public:
//struct SubTypeT {
struct SubType {
int i;
};
//typedef SubTypeT SubType;
private:
SubType m;
};
template<typename T>
typename T::SubType*f(){ return 0; }
int main() {
f<A>();
A a;
a.ff();
}
A class is fully defined at the closing brace, not at the point where you're listing its parent classes. Therefore, in class A : public TemplateBase< A > {
, you're instantiating TemplateBase
with an incomplete class A.
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