函数/方法签名后面的 const 是什么意思？

发布于 2024-08-07 14:10:54 字数 204 浏览 3 评论 0原文

根据 MSDN 的说法：“当遵循成员函数的参数列表时，const 关键字指定该函数不会修改调用它的对象。”

有人可以澄清一下吗？这是否意味着该函数不能修改对象的任何成员？

 bool AnalogClockPlugin::isInitialized() const
 {
     return initialized;
 }

原文

According to MSDN: "When following a member function's parameter list, the const keyword specifies that the function does not modify the object for which it is invoked."

Could someone clarify this a bit? Does it mean that the function cannot modify any of the object's members?

 bool AnalogClockPlugin::isInitialized() const
 {
     return initialized;
 }

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你列表最软的妹 2024-08-14 14:10:54

这意味着该方法不会修改成员变量（声明为可变的成员除外），因此可以在类的常量实例上调用它。

class A
{
public:
    int foo() { return 42; }
    int bar() const { return 42; }
};

void test(const A& a)
{
    // Will fail
    a.foo();

    // Will work
    a.bar();
}

It means that the method do not modify member variables (except for the members declared as mutable), so it can be called on constant instances of the class.

class A
{
public:
    int foo() { return 42; }
    int bar() const { return 42; }
};

void test(const A& a)
{
    // Will fail
    a.foo();

    // Will work
    a.bar();
}

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软糯酥胸 2024-08-14 14:10:54

另请注意，虽然成员函数无法修改未标记为可变的成员变量，但如果成员变量是指针，则成员函数可能无法修改指针值（即指针指向的地址），但它可以修改指针指向的内容（实际的内存区域）。

例如：

class C
{
public:
    void member() const
    {
        p = 0; // This is not allowed; you are modifying the member variable

        // This is allowed; the member variable is still the same, but what it points to is different (and can be changed)
        *p = 0;
    }

private:
    int *p;
};

Note also, that while the member function cannot modify member variables not marked as mutable, if the member variables are pointers, the member function may not be able to modify the pointer value (i.e. the address to which the pointer points to), but it can modify what the pointer points to (the actual memory region).

So for example:

class C
{
public:
    void member() const
    {
        p = 0; // This is not allowed; you are modifying the member variable

        // This is allowed; the member variable is still the same, but what it points to is different (and can be changed)
        *p = 0;
    }

private:
    int *p;
};

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