编译器错误：“非静态成员引用必须相对于特定对象”

Question

I've been trying to learn how to declare functions inside a class in CPP:

This is the program I wrote:

    //Passing object as function arguments and returning objects
#include <iostream>
using namespace std;
class item{ //Function can be declared either within the class (in that case, there is no need of making the data private)
    int price;
    float cost;
    public:
    int newFunction(item a){
        a.cost=10;
        a.price=40;
        return a.cost;
    }
} obj1;
int main(){
    cout << item::newFunction(obj1);
    return 0;
}

Can someone tell why does the compiler give error "a nonstatic member reference must be relative to a specific object".

Also, can someone tell the difference between:: (scope resolution operator) and accessing class elements using.(dot operator). I am sort of confused between the two, and Googling the difference didn't bring any matchable results.

Answer 1

Heres your answer:-

Error Message:

14:35: error: cannot call member function 'int item::newFunction(item)' without object

You can't just call a class function without making any object of it because you cannot directly access a class function if its not created in RAM first, thats why we create a object of a class.

I made a temporary object in main function named obj2 and it works.

Heres the added line

#include <iostream>
using namespace std;

class Item { //Function can be declared either within the class (in that case, there is no need of making the data private)
    int price;
    float cost;

public:

    int newFunction(item a) {
        a.cost=10;
        a.price=40;
        return a.cost;
    }

} obj1;
int main() {
    Item obj2;
    cout << obj2.newFunction(obj1);
    return 0;
}

Output:

10

Also its not a good practice to not use camelcase in naming a class, so do keep that in mind:)

Heres your answer What is the difference between "::" "." and "->" in c++

Answer 2

cout << item::newFunction(obj1); This only works when you declare the newFunction() as static . Otherwise, if you would like to call the member function, you have to create an object. item Obj; And then call Obj.newFunction(obj1);