Question

#include <iostream>
#include <cstring>
#include <QString>
using namespace std;

class A {
public:
    static const int i = 9;
    static const int PI = 1.3;
    static const char ch = 's';
    static const string str = "hello world"; // <--- error
    static const QString str2 = "hello world"; // <--- error
};

int main(int argc, char **argv) {
    cout << "Hello world" << endl;

    return 0 ;
}

As the code gives everything, how can I init a string.

Answer 1

Non-integral type members (that includes string and your user-defined types), need to be initialized outside the class definition, in a single implementation file (.cc or .cpp usually).

In your case, since you didn’t separate the class definition in a header, you can initialize the statics right after your class:

class A {
public:
    static const int i = 9;
    static const int PI = 1.3;
    static const char ch = 's';
    static const string str;
    static const QString str2;
};


const string A::str = "hello world";
const QString A::str2 = "hello world";

EDIT: Besides this, as Nawaz pointed out, the header file that defines string is <string>, not <cstring>.