c++ - 常量字段中的初始化列表不生成 operator=

Question

由于某些原因，由于const字段_constFoo的初始化，编译器无法为此类生成operator=，我只想知道为什么。使用 VS2010。

class Foo {
public:
    Foo(int f) : _constFoo(f) { }
    int getFoo() const { return _constFoo; }
    //void operator=(const Foo &f) { memcpy(this, &f, sizeof(Foo)); }
private:
    const int _constFoo;
};

int main(int argc, char *argv[])
{
    Foo f(5);
    cout << f.getFoo() << endl;
    f = Foo(6); //error C2582: 'operator =' function is unavailable in 'Foo'
    cout << f.getFoo() << endl;
}

Answer 1

标准不允许:

C++03 12.8。复制对象

12) [...] A program is ill-formed if the class for which a copy assignment operator is implicitly defined has:

• a non-static data member of const type, or
• a non-static data member of reference type, or
• a non-static data member of class type (or array thereof) with an inaccessible copy assignment operator, or
• a base class with an inaccessible copy assignment operator.

[...]

强调我的。

所以你的程序格式错误。通过不定义您自己的赋值运算符，编译器会尝试隐式定义一个。