C ++中单独文件中的类？

Question

I have copied this out of a book. I'm just not sure what to add in the main.cpp source file to make it run though.

I know that class declarations go in the .h file and implementations go in the .cpp file. What would I need to write in main.cpp ?

I've tried lots of different things but I'm just getting so many error messages.

 // cat.h
#ifndef ____2_cat_implementation__Cat__
#define ____2_cat_implementation__Cat__

#include <iostream>
using namespace std;
class Cat
{
public:
Cat (int initialAge);
~Cat();
int GetAge() { return itsAge;}              
void SetAge (int age) { itsAge = age;}      
void Meow() { cout << "Meow.\n";}          
private: int itsAge;
};

#endif /* defined(____2_cat_implementation__Cat__) */

...

// cat.cpp
#include <iostream>
#include "Cat.h"
using namespace std;

Cat::Cat(int initialAge) 
{
itsAge = initialAge;
}

Cat::~Cat() 
{

}

int main()
{
    Cat Frisky(5);
    Frisky.Meow();
    cout << "Frisky is a cat who is ";
    cout << Frisky.GetAge() << " years old.\n";
    Frisky.Meow();
    Frisky.SetAge(7);
    cout << "Now Frisky is " ;
    cout << Frisky.GetAge() << " years old.\n";
    return 0;
}

Answer 1

Look at this part again:

Cat::Cat(int initialAge); 
{
itsAge = initialAge;

Cat::~Cat() 

You're missing the closing } for the constructor, as well as an extra ; after the function header.

On an unrelated note, don't use global names starting with underscore (like ____2_cat_implementation__Cat__ ), those names a reserved by the specification.

Answer 2

You have a missing } and unneccessary ;

  //----------------------v
  Cat::Cat(int initialAge); 
  {
      itsAge = initialAge;
  }
//^

---

What would I need to write in main.cpp

Usially, as you have pointed out, the .h file contains the declarations and the .cpp file - the definitions. Then, the main.cpp file should contain the main function (it's not necessary to name the file, containing the main function main.cpp . It could be anything.

So, in your example, you can create a main.cpp file with the following content:

// include the declarations file
#include "cat.h"

// include the header for cin/cout/etc
#include <iostream>

using namespace std;

int main()
{
    Cat Frisky(5);
    Frisky.Meow();
    cout << "Frisky is a cat who is ";
    cout << Frisky.GetAge() << " years old.\n";
    Frisky.Meow();
    Frisky.SetAge(7);
    cout << "Now Frisky is " ;
    cout << Frisky.GetAge() << " years old.\n";
    return 0;
}

---

Other notes:

• using namespace std; is bad practice, especially in header files. Use std:: instead (for example, std::cout , std::cin , std::string , etc)
• as you have .h and .cpp files, don't put half of the implementation in the header and the rest - in the source file. Put all definitions inside the source files (unless you want to inline the functions, implemented in the header)
• avoid using names, starting with __ or _ - they are reserved by the standard.