Why are the constructor and destructor declared outside of the header file? What are the advantages to excluding it from the header file?

[code]
1: #include <iostream.h>
2: class Cat
3: {
4: public:
5: Cat (int initialAge);
6: ~Cat();
7: int GetAge() { return itsAge;} // inline!
8: void SetAge (int age) { itsAge = age;} // inline!
9: void Meow() { cout << "Meow.\n";} // inline!
10: private:
11: int itsAge;
12: };
[/code]

[code]
1: // Demonstrates inline functions
2: // and inclusion of header files
3:
4: #include "cat.hpp" // be sure to include the header files!
5:
6:
7: Cat::Cat(int initialAge) //constructor
8: {
9: itsAge = initialAge;
10: }
11:
12: Cat::~Cat() //destructor, takes no action
13: {
14: }
15:
16: // Create a cat, set its age, have it
17: // meow, tell us its age, then meow again.
18: int main()
19: {
20: Cat Frisky(5);
21: Frisky.Meow();
22: cout << "Frisky is a cat who is " ;
23: cout << Frisky.GetAge() << " years old.\n";
24: Frisky.Meow();
25: Frisky.SetAge(7);
26: cout << "Now Frisky is " ;
27: cout << Frisky.GetAge() << " years old.\n";
28: return 0;
29: }[/code]

*shrug* the same reason any other functions are defined outside their respective header files.

Some compilers may generate more than one instance of a function if it's defined in the header file. The function may also always be inlined. If the function is not defined in the header file, it mostly can't be inlined.