Question

Inside FileThree.h

#ifndef FILETHREE
#define FILETHREE
namespace blue{}
class Filethree
{
public:
    Filethree(void);
    ~Filethree(void);
};
#endif

Inside FileThree.cpp

#include "Filethree.h"
#include<iostream>
using namespace std ;
namespace blue{
     void blueprint(int nVar){
         cout<<"red::"<<nVar<<endl;
     }
}
Filethree::Filethree(void)
{
}

Filethree::~Filethree(void)
{
}

Inside FileFour.h

#ifndef FILEFOUR
#define FILEFOUR
namespace red{}
class FileFour
{
public:
    FileFour(void);
    ~FileFour(void);
};
#endif

Inside FileFour.cpp

#include "FileFour.h"
#include<iostream>
using namespace std; 
 namespace red{
     void redprint(double nVar){
         cout<<"red::"<<nVar<<endl;
     }
}
FileFour::FileFour(void)
{
}

FileFour::~FileFour(void)
{
}

Inside main.cpp

#include "FileFour.h"
 #include "Filethree.h"
using namespace red ;
using namespace blue ;

int main()
{
    blueprint(12);
return 0;
}

When i compile the above file it gives me the following error .

 error C3861: 'blueprint': identifier not found

Can anyone tell me why i am getting this error ?

Answer 1

Compiler can’t find functions when they are not declared in header files.
You need to declare blueprint function in namespace blue in FileThree.h

FileThree.h:

namespace blue{
    void blueprint(int nVar);
}

Same to redprint function, need to declare it in FileFour.h inside namespace red

FileFour.h

namespace red{
   void redprint(double nVar);
}