初始化全局变量类 [英] Initializing global variable class

问题描述

对这样一个基本问题道歉，但我不能弄清楚。我知道你可以初始化这样的类：

Apologies for such a basic question but I can't figure it out. I know you can initialize a class like this:

QFile file("C:\\example");

但是如何从全局变量初始化它呢？例如：

But how would you initialize it from a global variable? For example:

QFile file; //QFile class

int main()
{
    file = ?? //need to initialize 'file' with the QFile class
}

推荐答案

1。直接回答

如果类是可分配的/可复制的，可以写

1. Straightforward answer

If the class is assignable/copy constructible you can just write

QFile file; //QFile class

int main()
{
    file = QFile("C:\\example");
}

2。使用间接

如果没有，您必须使用其他选项：

2. Use indirection

If not, you'll have to resort to other options:

QFile* file = 0;

int main()
{
    file = new QFile("C:\\example");

    //
    delete file;
}

或使用 boost :: optional< QFile> ， std :: shared_ptr< QFile> ， boost :: scoped_ptr< QFile>

由于静态初始化Fiasco 您可能想要编写这样的函数：

Due to the Static Initialization Fiasco you could want to write such a function:

static QFile& getFile()
{ 
    static QFile s_file("C:\\example"); // initialized once due to being static
    return s_file;
}

C ++ 11使得这样的函数局部静态初始化线程安全（引用C ++ 0x草案n3242，§6.7：）

C++11 made such a function-local static initialization thread safe as well (quoting the C++0x draft n3242, §6.7:)

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