'ClassName' 不命名类型

Question

I have seen similar answers, but I don't seem to be able to solve mine just by looking at these for example ( this or that one for example).

So, I am having that .

Ah

#ifndef INCLUDE_CLASS_NAME
#define INCLUDE_CLASS_NAME

#include <B.h>

using namespace C;

D::DPtr myvariable;  <-- Error in here

#endif

In the include Bh I have this :

namespace C{
namespace E{

class D
{
  public:
      typedef shared_ptr<D> DPtr;
}

} //end of namespace E
} // end of namespace C

Why am I getting this error in the mentioned line :

'D'  does not name a type

I am including the .h file, which defines the class. What am I missing?

Answer 1

The symbol D is inside namespace E , which is inside namespace C , so the fully qualified name is C::E::D .

So either:

• Add E:: to refer to D correctly:

   mutable E::D::DPtr myvariable;

• Declare E in the using directive as well:

   using namespace C::E;

Answer 2

你错过了命名空间 E...

mutable E::D::DPtr myvariable; // should work

Answer 3

You're trying to call a function that does not exist yet according to the preprocessor. You need to define functions before you call them:

int mainFunction(){
    int foo(int bar){ //define function FIRST...
        return bar;
    }
foo(42) //call it later.
}

This should get rid of the error. This does not:

int mainFunction(){
    foo(42) //trying to call a function before it's declared does not work.
        int foo(int bar){
        return bar;
    }
}