c ++如何正确地将.cpp拆分为.cpp和.h

Question

I'm really new to splitting a .cpp into a .cpp and a .h.

I've used .h files before, but never really split a .cpp into a .cpp and a .h.

I know .h files are only for declarations and .cpp are for definitions, and I attempted to split a .cpp into a .cpp and a .h but I get a lot of errors, so I was wondering if someone can help me with my code.

The following class is the class that has NOT yet been split into a .cpp and a .h yet, just to show you guys the "before version".

TicketOrder.cpp

#include <iostream>

using namespace std;

class TicketOrder
{

private :

        char type;
        int quantity;

public :

          friend std::ostream& operator<<(std::ostream& os, TicketOrder const& order)
         {
                 os << " Type: " << order.type << ", Quantity: " << order.quantity;
                 return os;
         }


        //Getters

        int getQuantity() const;
         {
                        return quantity;
         }

        char getType() const;
          {
                        return type;
          }

        //Setters    

        void setQuantity (int x)
                {
                        quantity =x;
                }

        void setType(char y)
                {
                        type =y;
                }   
};

Now, I will split that above class into a .cpp and a .h

TicketOrder.cpp

#include <iostream>
#include "TicketOrder.h"
using namespace std;

class TicketOrder
{

        //Getters

        int getQuantity() const
                {
                        return quantity;
                }

        char getType() const
                {
                        return type;
                }

        //Setters

        void setQuantity (int x)
                {
                        quantity =x;
                }

        void setType(char y)
                {
                        type =y;
                }        
};

TicketOrder.h

#include <iostream>

using namespace std;

class TicketOrder
{

private :

        char type;
        int quantity;

public :

          friend std::ostream& operator<<(std::ostream& os, TicketOrder const& order)
        {
                 os << " Type: " << order.type << ", Quantity: " << order.quantity;
                 return os;
        }

        //Getters

        int getQuantity() const;    
        char getType() const;

        //Setters

        void setQuantity (int x);    
        void setType(char y);       
};

I have one other class that is used to contain the main class that I will not include in here because it's long and I do not think it's important because I know I'm doing the .h and .cpp wrong.

When I try to compile the main, it gives me this error:

Undefined                       first referenced
 symbol                             in file
TicketOrder::getQuantity() const    /var/tmp//ccaSflFG.o
TicketOrder::setType(char)          /var/tmp//ccaSflFG.o
TicketOrder::setQuantity(int)       /var/tmp//ccaSflFG.o
ld: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status

Can anyone help me with splitting the .h and the .cpp? Or give me suggestions? I did a lot of research and can't figure out what's wrong.

Thank you.

Answer 1

Your .cpp file is wrong because is re-declaring the class, so that's and error. It should be something along the lines of:

#include <iostream>
#include "TicketOrder.h"
using namespace std;

//Getters
int TicketOrder::getQuantity() const
{
    return quantity;
}
char TicketOrder::getType() const
{
    return type;
}

//and so on

Also, note that adding a using namespace in a header file, as you are doing is, considered very bad style.

Answer 2

You can play with lzz , it does exactly this automatically. In it's default mode it will show you more or less where things usually go.

Answer 3

You can do this very successfully if you just take care of these few tips

1. Your .cpp files should contain your main function
2. Your .h file should contain the header files
3. Your .cpp(ie your program) should declare all the headerfile names in the top
4. Your .h file should contain any other headerfiles needed in the functions in the .h file
5. When you compile the .h file it may show some error but don't acre that. It is because it does not contain the main function.

Answer 4

Rodrigo already addressed your main problem. Let me just add some style comment:

• you don't need using namespace std , since you are already addressing the std members with the std:: prefix. In my opinion this is (almost) always the best solution, since the using namespace X directive could be inherited by some other files that include your .h file.
• if you really want to use using namespace std , place that directive inside your class, so that other files that include yours won't have it. They might define functions/classes with the same name of the std ones, which would cause compilation errors if there is a using namespace std directive above...
• your .cpp file does not need to include <iostream> , since it's already included in the header... Yes, <iostream> has for sure a header guard, so it's not really included twice. But I think it's nice to not include what's already included in the header... But maybe it's just my taste... ;-)