全局静态变量vs函数中的静态变量？

Question

What's the diference between use:

static Foo foo;
// ...
foo.func();

And:

Foo& GetFoo(void) 
{
    static Foo foo;
    return foo;
}

// ...

GetFoo().func();

Which is better?

Answer 1

The principal difference is when construction occurs. In the first case, it occurs sometime before main() begins. In the second case, it occurs during the first call to GetFoo() .

It is possible, in the first case, for code to (illegally) use foo prior to its initialization. That is not possible in the second case.

Answer 2

A GetFoo is generally used when you don't want copies of your class/object. For example:

class Foo
{
private:
    Foo(){};
    ~Foo();
public:
    static Foo* GetFoo(void) 
    {
        static Foo foo;
        return &foo;
    }

    int singleobject;
};

You can externally access singleobject via Foo::GetFoo()->sinlgeobject . The private constructors and destructors avoid your class getting copies created.

For the use of static Foo foo , you must have public constructors declared which means you are always accessing your class by it, but your class will also be able to get copies.