C++ define class in head file, and implement its member in source file

Question

when i build this project in vs2010, error occurs:

1. syntax error : missing ';' before identifier 'b'
2. error C4430: missing type specifier - int assumed. Note: C++ does not support default-int
3. error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

4. error C2065: 'b' : undeclared identifier

   #ifndef _B_H
   #define _B_H
   
   #include <string>
   
   class B
   {
   public:
       B();
       ~B();
       void showfunc();
   
       string b;
   };
   
   #endif
   
   /***************************/
   // B.cpp
   #include <iostream>
   #include <string>
   #include "B.h"
   using namespace std;
   B::B()
   {
   }
   void B::showfunc()
   {
    cout<<b<<endl;
   }
   /**************************************/
   // main.cpp
   #include <iostream>
   // #include "B.h"
   using namespace std;
   void main()
   { 
   }
   

Please help me!

Answer 1

string is in the std namespace. You need

std::string b; 

You should also be be careful with using namespace std, even in implementation files.

Also, note that void main() is not one of the standard signatures for main in C++. You need

int main() { ...

Answer 2

add std to string

std::string b;