understanding overloaded operators

[luki]

I've seen these lines of codes before on the internet, they seem to be related to overloaded operators and objects of the library iostream but what do they actually do ?:

1) std::ostream& print(std::ostream &ostr) const;

2) std::ostream& operator<< (std::ostream &ostr, const [class_type] &[class_name]);

3) std::istream& operator>> (std::istream &istr, [class_type] &[class_name]);

4)operator- (const [class_type] &x1, [class_type] &x2)

p.s the [] are not part of the code, they just indicate where the class names and types are placed.

[Bazzy]

1) looks as a class method, it's not related to operator overloading

2-3) they are used to provide streams operators for some user defined types
eg (use of those overloaded operators):

mytype mt;
cin >> mt;//get someway a value from the user
cout << mt;//display the value of 'mt' 

4) used to do subtraction from two objects of used defined types


eg:

struct S
{
    int member;
    S(int i):member(i){}
};
S operator- (const S &x1, const S &x2)//Could also be made a member of 'S' in this case
{
    return S(x1.member-x2.member);
}
ostream &operator << (ostream &os, const S &s)
{
    return os << s.member;
}

S a=5, b=3, c = a-b;
cout << c;//should show 2