构造函数中的 C++ 单例

Question

这可能吗？

class A {
    static A *instance = NULL;

public:
    A () {
        if (instance) {
            this = instance;
        } else {
            instance = this;
        }
    }
}

是否有内存泄漏？

我需要重载 new 运算符吗？

Answer 1

没有。忽视你的编译器错误，你的类将无法工作。

@Galik has provided invaluable sources了解您实际想要构建单例的方式。但是让我们看看你的。

class A {
    static A *instance = NULL; // NULL isn't even a thing, but assuming you mean nullptr you can't assign a static like this

public:
    A () {
        if (instance) {
            this = instance; // this can't be assigned
        } else {
            instance = this; // this is correct
        }
    }
};

这会给你以下内容:

class A {
    static A *instance;

public:
    A () {
        // if there's no instance, this is the one we'll use
        if (!instance) {
            instance = this;
        }
    }
};

A* A::instance = nullptr;

无论如何，这并不能阻止您构建多个。