关于class内定义inline的问题

#pragma once

#include<iostream>

#include<string>

class Triangular_iterator

{

public:

Triangular_iterator(int index) :_index(index - 1) {}

bool operator== (const Triangular_iterator&) const;

bool operator!=(const Triangular_iterator&) const;

int operator*()const;

Triangular_iterator& operator++();

Triangular_iterator operator++(int);

//inline void check_integrity()const;

private:

inline void check_integrity()const;

int _index;

};