在C ++中初始化Class的成员变量的位置

Question

I just started using C++. I have a question. Where should I initialize class member variables? I have assigned some value to members variables using some member function. But static analysis tool is complaining about member initialization in constructor. See following example:

test.cpp

#include<iostream>
using namespace std;

class Point {
private:
    int x;
    int y;
public:
    Point(int r)
    {
      y = r;
    } 

    inline void setXval(int x_val) {
       x = x_val;
    }
};

Here, that tool says that x is not initialized in constructor. But I am setting x value in member function. Is it correct way to do this or we should always initialize all members in default constructor? Any help is much appreciated. Thanks in advance !

Answer 1

All variables should get an explicit value in the constructor. You're not giving any value to x , so your tool is correct. You might or might not call the member function that sets the value for x later - You cannot count that you (or a user of your code) will call that function before you need the value of x somewhere.

Answer 2

Your tool want that you use initializer list:

class Point {
private:
    int x;
    int y;
public:
    Point(int x, int y) : x(x), y(y) {}
};

Answer 3

You should construct every class member in a constructor. Member functions can change class members' values, but it can't construct them.

Point(int _x, int _y): x(_x), y(_y) {}