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const in class meaning

csstudent123 (409)
Hi. Whats the use of using int funct() const; in class declaration? Because my class functions work even without using const.

Also what is meaning of int& funct(); the ampersand does it return address? if so of what?
Last edited on
JLBorges (13770)
helios (17575)
const is used to control the ability of code to make accidental changes to data. You should declare your functions as const whenever possible, and when passing by reference you should try to pass by const T & whenever possible.

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class A{
    int a;
public:
    A(): a(0){}
    void f0(){
        //OK
        this->a++;

        //OK
        this->f2();

        //OK
        this->f3(); 
    }
    void f1() const{
        //Error. const functions can't modify members.
        this->a++;

        //Error. const functions can't call non-const functions.
        this->f2();

        //OK
        this->f3();
    }
    void f2(){
    }
    void f3() const{
    }
};

int main(){
    A a;
    const A &b = a;

    //OK
    a.f2();

    //OK
    a.f3();

    //Error. Can't call non-const functions on const objects.
    b.f2();

    //OK
    b.f3();
}
Last edited on
csstudent123 (409)
What the const T&? whats T?
helios (17575)
'T' is a common placeholder for an arbitrary type.
csstudent123 (409)
you mean typedef type T?
helios (17575)
No.
typedef type T
In your example, you're using the word "type" in the same way I was using the letter 'T'. It's a placeholder.
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