C + + language Learning (v) CV qualifier errors in--c++ languages

C + + language Learning (v) CV qualifier error in--c++ language? Introduction to CV Qualifier Error 1, CV qualifier Introduction

The CV qualifier is the const and volatile qualifier in the cv-qualifier,c++ language.
In general, there are two cases in the C + + language that cannot be qualified with CV qualifiers:
A, non-member functions cannot use CV-qualification
B, static member functions cannot use CV-qualification

2. Introduction to CV qualifier error messages

CV Qualifier error information in the C + + language such as "Cannot has cv-qualifier", the common CV qualifier error message is as follows:
CV-Qualifier error message for a, non-member function
error: non-member function ‘xxxxxxxxx‘ cannot have cv-qualifier
B, CV-qualifier error information for static member functions
error: static member function ‘static xxxxxxx‘ cannot have cv-qualifier

II. CV-Limited applications for C + + 1, non-member functions

In C + +, non-member functions cannot contain CV-qualifiers, which are const and volatile qualifiers.

#include <iostream>using namespace std;double sum(double a, double b)const{    return a + b;}//error: non-member function ‘double sum(double, double)‘ cannot have cv-qualifierint main(int argc, char *argv[]){    double a = 3.14;    double b = 2.0;    double ret = sum(a, b);    return 0;}

The above code is an error, and the non-member function sum cannot be qualified with Const.

#include <iostream>using namespace std;double sum(double a, double b)volatile{    return a + b;}//error: non-member function ‘double sum(double, double)‘ cannot have cv-qualifierint main(int argc, char *argv[]){    double a = 3.14;    double b = 2.0;    double ret = sum(a, b);    return 0;}

The above code is an error, and the non-member function sum cannot be qualified with volatile.
A non-member function cannot use const and volatile to restrict a function, but the return value of a function or function can be qualified with const and volatile.

#include <iostream>using namespace std;volatile double sum(double a, double b){    volatile double c = a + b;    return c;}int main(int argc, char *argv[]){    double a = 3.14;    double b = 2.0;    double ret = sum(a, b);    return 0;}

The friend function of a class is not a member function of a class, and a friend function cannot be restricted with const and volatile.

#include <iostream>using namespace std;class Test{private:    static int data;public:    Test()    {        data++;    }    //静态成员函数    static int count()    {        return data;    }    friend int getValue()const;//error    //error: non-member function ‘int getValue()‘ cannot have cv-qualifier    ~Test()    {        data--;    }};int Test::data = 0;//error: non-member function ‘int getValue()‘ cannot have cv-qualifierint getValue()const//error{    return Test::data;}int main(int argc, char *argv[]){    cout << Test::count() << endl;    Test test;    cout << test.count() << endl;    return 0;}

The above code error, Class of friend function GetValue cannot use const and volatile to qualify.

2. Static member functions

In C + +, static member functions cannot be CV-qualified, that is, const and volatile.

#include <iostream>using namespace std;class Test{private:    static int data;public:    Test()    {        data++;    }    //静态成员函数    static int count()const    {        return data;    }    //error: static member function ‘static int Test::count()‘ cannot have cv-qualifier    ~Test()    {        data--;    }};int Test::data = 0;int main(int argc, char *argv[]){    cout << Test::count() << endl;    Test test;    cout << test.count() << endl;    return 0;}

The above code error, the static member function of the class count cannot be qualified with the Const keyword.

#include <iostream>using namespace std;class Test{private:    static int data;public:    Test()    {        data++;    }    //静态成员函数    static int count()volatile    {        return data;    }    //error: static member function ‘static int Test::count()‘ cannot have cv-qualifier    ~Test()    {        data--;    }};int Test::data = 0;int main(int argc, char *argv[]){    cout << Test::count() << endl;    Test test;    cout << test.count() << endl;    return 0;}

The above code error, the static member function of the class count cannot be qualified with volatile keywords.

C + + language Learning (v) CV qualifier errors in--c++ languages