如何解决“'（'令牌之前的声明中的qualified-id”错误？

Question

我是C ++类和对象的初学者。我想定义函子，并根据“ corv”类的构造值的类型将其定义为具有不同的功能。 ab函子可用于int，ch函子可用于char，re函子可用于string。

下面是我的代码：

#include <iostream>
using std::string;
using std::cout;

// "ab" functor

class ab {
private:
    int val;
public:
    ab(int v) : val(v) {}
    void operator()() const;
};

// "ch" functor

class ch {
private:
    char val;
public:
    ch(char v) : val(v) {}
    void operator()() const;
};

// "re" functor

class re {
private:
    string val;
public:
    re(string v) : val(v) {}
    void operator()() const;
};

// corv class

class corv {
private:
    string t;
    int intV;
    char charV;
    string stringV;
public:
    // constructor for "int" value
    corv(int v) {
        // only "ab" functor available
        intV = v;
        t = "int";
        void ab::operator()() const {
            cout << "ab: " << val << endl;
        }
        void ch::operator()() const {
            return;
        }
        void re::operator()() const {
            return;
        }
    }

    // constructor for "char" value
    corv(char v) {
        // only "ch" functor available
        charV = v;
        t = "char";
        void ab::operator()() const {
            return;
        }
        void ch::operator()() const {
            cout << "ch: " << val << endl;
        }
        void re::operator()() const {
            return;
        }
    }

    // constructor for "string" value
    corv(string v) {
        // only "re" functor available
        stringV = v;
        t = "string";
        void ab::operator()() const {
            return;
        }
        void ch::operator()() const {
            return;
        }
        void re::operator() const {
            cout << "re: " << val << endl;
        }
    }
};

这些错误

test.cpp: In constructor 'corv::corv(int)':
test.cpp:39:28: error: qualified-id in declaration before '(' token
         void ab::operator()() const {
                            ^
test.cpp:42:28: error: qualified-id in declaration before '(' token
         void ch::operator()() const {
                            ^
test.cpp:45:28: error: qualified-id in declaration before '(' token
         void re::operator()() const {
                            ^
test.cpp: In constructor 'corv::corv(char)':
test.cpp:52:28: error: qualified-id in declaration before '(' token
         void ab::operator()() const {
                            ^
test.cpp:55:28: error: qualified-id in declaration before '(' token
         void ch::operator()() const {
                            ^
test.cpp:58:28: error: qualified-id in declaration before '(' token
         void re::operator()() const {
                            ^
test.cpp: In constructor 'corv::corv(std::__cxx11::string)':
test.cpp:65:28: error: qualified-id in declaration before '(' token
         void ab::operator()() const {
                            ^
test.cpp:68:28: error: qualified-id in declaration before '(' token
         void ch::operator()() const {
                            ^
test.cpp:71:29: error: qualified-id in declaration before 'const'
         void re::operator() const {
                             ^~~~~

发生过。

为什么？以及如何解决这个问题？