在C ++中初始化类中的非原始静态数据类型

Question

#include <QQueue>
#include <QString>

class   Util {
public:

    static QQueue<QString> links;

    Util() {
    }
};

    Util::links.enqueue("hello world");

How can I do that?

Answer 1

You could initialise it with the result of a function:

QQueue<QString> make_links() {
    QQueue<QString> queue;
    queue.enqueue("hello world");
    return queue;
}

QQueue<QString> Util::links = make_links();

I'm not familiar with QT, but one might hope that they are adding support for C++11 initialiser lists, in which case you'd be able to initialise it as:

QQueue<QString> Util::links {"hello world"};

(UPDATE: according to the link in Shahbaz's comment, you can indeed do that if you are using C++11).

Answer 2

Try using a static member function:

#include <QQueue>
#include <QString>

class   Util {
public:

    static QQueue<QString>& links() {
      static QQueue<QString> instance;
      static bool is_init = false;
      if(!is_init) {
        instance.enqueue("hello world");
        is_init = true;
      }
      return instance;
    }

    Util() {
    }
};

In C++11 QQueue seems to support initializer lists, as Shahbaz has said:

QQueue<QString> Util::links = {"hello world"};

Answer 3

You can use static initializer object for all such cases:

header file:

#include <QQueue>
#include <QString>

class   Util {
public:

    static QQueue<QString> links;

    Util() {
    }
};

cpp file:

namespace {
    struct StaticInitializer {
        StaticInitializer() {
            Util::links.enqueue("hello world");
        }
    } initializer;
}

Answer 4

You initialize as usual, in the global scope:

QQueue<QString> Util::links;

or

QQueue<QString> Util::links(1); // with constructor parameters if necessary