c++ - 循环中的 "Ambiguous Overload"问题和故障 cin

Question

我正在构建一个带有成员函数的菜单创建类，该类应该显示菜单、从用户那里获得选择、测试它是否是一个有效的菜单项并返回项目的编号。出于某种原因，编译器在下面的 run() 成员函数中的一个简单 cin 语句上给我一个“运算符 '>>' 的模糊重载”错误。运行时，该函数会正确捕获无效输入，但随后会考虑无效输入之后的所有输入。如果第一个输入是正确的，程序将立即终止。这是我的代码:

#include <iostream>
#include <vector>

using namespace std;

class NumericalMenu {
private:
    string prompt;
    vector<string> options;
    string canceltext;
    string errortext;
    bool repeatprompt;
    int sel;
public:
    NumericalMenu() {
        prompt = "Choose an option:";
        canceltext = "Cancel";
        errortext = "Error!";
        repeatprompt = true;
        sel = 0;
    };
    void setPrompt(string text) {
        prompt = text;
    };
    int size() const {
            int size = options.size() + 1;
            return size;
        };
    int addOption(string text) {
        options.push_back(text);
        int position = options.size() - 1;
        return position;
    };
    void setCancelText(string text) {
        canceltext = text;
    };
    void setRepeatPromptOnError(bool repeat) {
        repeatprompt = repeat;
    };
    void setErrorText(string text) {
        errortext = text;
    };

    int run() const{
        cout << prompt << "\n\n";
        for (unsigned i=0; i<options.size(); i++) {
            cout << i+1 << " - " << options[i] << "\n";
        }
        int errorpos = this->size();
        cout << errorpos << " - " << canceltext << "\n\n";

        cin.clear();
        cin.ignore();
        cin >> sel;

        if(cin.fail() || sel<=0 || sel>errorpos) {
            cout << "\n" << errortext << "\n\n";
            if(repeatprompt == true) {
                cin.clear();
                cin.ignore();
                this->run();
            }
        }
        if (sel == errorpos) {
            return -1;
        } else {
            return sel;
        }

    };

};

int main() {
    NumericalMenu menu;
    menu.setPrompt("Choose an option:");
    menu.addOption("Enter new values");
    menu.addOption("Help");
    menu.addOption("Save");
    menu.setCancelText("Exit");
    menu.run();
}

编辑:知道了!感谢大家。工作标题:

#include <iostream>
#include <vector>
#include <string>

using namespace std;

class NumericalMenu {
private:
    string prompt;
    vector<string> options;
    string canceltext;
    string errortext;
    bool repeatprompt;

public:
    NumericalMenu() {
        prompt = "Choose an option:";
        canceltext = "Cancel";
        errortext = "Error!";
        repeatprompt = true;

    };
    void setPrompt(string text) {
        prompt = text;
    };
    int size() const{
            int size = options.size() + 1;
            return size;
        };
    int addOption(string text) {
        options.push_back(text);
        int position = options.size() - 1;
        return position;
    };
    void setCancelText(string text) {
        canceltext = text;
    };
    void setRepeatPromptOnError(bool repeat) {
        repeatprompt = repeat;
    };
    void setErrorText(string text) {
        errortext = text;
    };

    int run() const{
        cout << prompt << "\n\n";
        for (unsigned i=0; i<options.size(); i++) {
            cout << i+1 << " - " << options[i] << "\n";
        }
        int errorpos = this->size();
        cout << errorpos << " - " << canceltext << "\n\n";

        int sel;
        cin.clear();
        cin >> sel;

        if(cin.fail() || sel<=0 || sel>errorpos) {
            cout << "\n" << errortext << "\n\n";
            if(repeatprompt == true) {
                cin.clear();
                cin.ignore(1000, '\n');
                int sele = this->run();
                return sele;
            }
        }

        if (sel == this->size()) {
            return -1;
        }

        else {
            return sel;
        }

    };

};

Answer 1

您声明了您的 run()用作const并防止对成员变量的修改由编译器强制执行。

class NumericalMenu {
private:
    int sel;
...
    int run() const {
        cin >> sel; // Not allowed

如果需要修改成员变量，去掉const在你的内联 run()函数定义。

此外，作为一种良好做法，请尝试在代码中包含您直接使用的所有 header (即 <string>)。