How to fix and compile this C++ program

Question

In nestClassDef.h I have written code like this

  class A{
    public:
     class B{
         public:
           void BTest();
     };
 };

   class B{

   };

then in the nestClassDef.cpp I am writing code like this

      #include "nestClassDef.h"
      #include<iostream>

      void A::B::BTest(){
        cout<<"Hello World!";
     }

    int main(){
      A a;
      A.B b;
      b.BTest();
    }

But when I am compiling the above code

       g++ -o nestClassDef nestClassDef.cpp

I am getting error like this :-

      nestClassDef.cpp: In member function ‘void A::B::BTest()’:
      nestClassDef.cpp:5: error: ‘cout’ was not declared in this scope
      nestClassDef.cpp: In function ‘int main()’:
      nestClassDef.cpp:10: error: expected unqualified-id before ‘.’ token
      nestClassDef.cpp:11: error: ‘b’ was not declared in this scope

I am at a loss how to fix this. Any understanding shared will be thankfully received.

At first I would consider indenting the code sensible. It's ignored by the compiler but helps human readers. Second you should specify the namespace, it's `std::cout`. — harper, Mar 08 '14 at 09:24
In case people suggest to write `using namespace std;`, read this first. It is usually [a terrible idea](http://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice). — juanchopanza, Mar 08 '14 at 09:25
Did you consider asking google about "error: ‘cout’ was not declared in this scope"? It gives hundreds of copies of the answer... — Marc Glisse, Mar 08 '14 at 09:26
I admit it's a mistake not to have referred google at first but I was compounded by two error messages so was little confused. — John Doe, Mar 08 '14 at 09:31
Thanks @juanchopanza lesson learnt will use the std::cout all the time. — John Doe, Mar 08 '14 at 09:34
When there are several errors, start with the first one. The others might just mean that the first error confused the compiler enough to start saying nonsense. — Marc Glisse, Mar 08 '14 at 12:52

score 2 · Answer 1 · answered Mar 08 '14 at 09:23

  nestClassDef.cpp: In member function ‘void A::B::BTest()’:
  nestClassDef.cpp:5: error: ‘cout’ was not declared in this scope

Use std::cout instead of cout, or add using namespace std; (probably after your #include statements).

  nestClassDef.cpp: In function ‘int main()’:
  nestClassDef.cpp:10: error: expected unqualified-id before ‘.’ token
  nestClassDef.cpp:11: error: ‘b’ was not declared in this scope

Use A::B instead of A.B.

score 2 · Accepted Answer · answered Mar 08 '14 at 09:25

2

For the cout error: it's in std namespace, so use std::cout.

For The second error: B is not A's member, it's a nested type, so you have to use A::B b;

answered Mar 08 '14 at 09:25

Michał Góral

1,439
2
16
30

score 1 · Answer 3 · answered Mar 08 '14 at 09:24

1

Add using namespace std; or use std::cout instead of just cout
Use A::B not A.B. Dot operator is used on objects or structs/unions.

answered Mar 08 '14 at 09:24

Engin Kayraklioglu

615
3
11

How to fix and compile this C++ program

3 Answers3