Ok, im reading Sams Teach yourself C++ in 21 days, overall i like it. But there is one thing i am highly confused by.
At the moment i am reading about passing by refrences, passing objects atm. And in the code example i am about to copy to you i do not understand what the copy constructor is for. That and the refrence opterator behind the class name (eg below)
Code:
public:
SimpleCat(); // original constructor
SimpleCat(SimpleCat&); // copy constructor
~SimpleCat(); // obviously deconstructor
So can someone help? Thanks!
Code:
1: //Listing 9.12
2: // Passing references to objects
3:
4: #include <iostream.h>
5:
6: class SimpleCat
7: {
8: public:
9: SimpleCat();
10: SimpleCat(SimpleCat&);
11: ~SimpleCat();
12:
13: int GetAge() const { return itsAge; }
14: void SetAge(int age) { itsAge = age; }
15:
16: private:
17: int itsAge;
18: };
19:
20: SimpleCat::SimpleCat()
21: {
22: cout << "Simple Cat Constructor...\n";
23: itsAge = 1;
24: }
25:
26: SimpleCat::SimpleCat(SimpleCat&)
27: {
28: cout << "Simple Cat Copy Constructor...\n";
29: }
30:
31: SimpleCat::~SimpleCat()
32: {
33: cout << "Simple Cat Destructor...\n";
34: }
35:
36: const SimpleCat & FunctionTwo (const SimpleCat & theCat);
37:
38: int main()
39: {
40: cout << "Making a cat...\n";
41: SimpleCat Frisky;
42: cout << "Frisky is " << Frisky.GetAge() << " years old\n";
43: int age = 5;
44: Frisky.SetAge(age);
45: cout << "Frisky is " << Frisky.GetAge() << " years old\n";
46: cout << "Calling FunctionTwo...\n";
47: FunctionTwo(Frisky);
48: cout << "Frisky is " << Frisky.GetAge() << " years old\n";
49: return 0;
50: }
51:
52: // functionTwo, passes a ref to a const object
53: const SimpleCat & FunctionTwo (const SimpleCat & theCat)
54: {
55: cout << "Function Two. Returning...\n";
56: cout << "Frisky is now " << theCat.GetAge();
57: cout << " years old \n";
58: // theCat.SetAge(8); const!
59: return theCat;
60: }
Output: Making a cat...
Simple Cat constructor...
Frisky is 1 years old
Frisky is 5 years old
Calling FunctionTwo...
FunctionTwo. Returning...
Frisky is now 5 years old
Frisky is 5 years old
Simple Cat Destructor...
so if you can, please expain to me the reason for the copy constructor existing, and what it is lol. Thanks! (that and the refrence operator behind SimpleCat (ie "(SimpleCat&)") thanks!