14.44 桌面计算器_桌面计数器 csdn-优快云博客

本文链接：https://blog.youkuaiyun.com/u014786409/article/details/102646965

本文探讨了在C++中使用函数指针和std::function进行数学运算的方法。通过创建映射表，将字符串操作符与对应的函数关联，实现了动态调用不同运算方式的功能。文章详细介绍了如何定义和使用函数指针及std::function，并展示了具体的代码实现。

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使用函数指针

#include <iostream>
#include <string>
#include <map>
#include <functional>

using namespace std;

enum cal_type {addop, minusop, multiop, divop};
map<const string, double(*)(int,int)> cal;
map<const string, cal_type> switcher;

double add_method(int a, int b) {
    return a+b;
}

double Minus_method(int a, int b) {
    return a-b;
}

double multi_method(int a, int b) {
    return a*b;
}

double div_method(int a, int b) {
    return a/b;
}

int main() {
    cal.insert(pair<const string, double(*)(int, int)>("add", add_method));
    cal.insert(pair<const string, double(*)(int, int)>("minus", Minus_method));
    cal.insert(pair<const string, double(*)(int, int)>("multi", multi_method));
    cal.insert(pair<const string, double(*)(int, int)>("div", div_method));

    switcher.insert(pair<const string, cal_type>("add", cal_type::addop));
    switcher.insert(pair<const string, cal_type>("minus", cal_type::minusop));
    switcher.insert(pair<const string, cal_type>("multi", cal_type::multiop));
    switcher.insert(pair<const string, cal_type>("div", cal_type::divop));

    string ret;
    int first, second;
    cout << "Enter the method and the values" << endl;
    while (cin >> ret >> first >> second) {
        switch (switcher[ret])
        {
            case cal_type::addop:
                cout << cal[ret](first, second) << endl;
                break;
            case cal_type::minusop:
                cout << cal[ret](first, second) << endl;
                break;
            case cal_type::multiop:
                cout << cal[ret](first, second) << endl;
                break;
            case cal_type::divop:
                cout << cal[ret](first, second) << endl;
                break;
            default:
                cout << "No match operator" << endl;
                break;
        }
    }

    return 0;
}

注意map cal中的second是函数指针，有*，而不是直接double(int, int)，这是一个函数类型，而不是函数指针类型。

使用function：

#include <iostream>
#include <string>
#include <map>
#include <functional>

using namespace std;

enum cal_type {addop, minusop, multiop, divop};
using func = function<double(int,int)>;
map<const string, func> cal;
map<const string, cal_type> switcher;

double add_method(int a, int b) {
    return a+b;
}

double Minus_method(int a, int b) {
    return a-b;
}

double multi_method(int a, int b) {
    return a*b;
}

double div_method(int a, int b) {
    return a/b;
}

int main() {
    cal.insert(pair<const string, func>("add", add_method));
    cal.insert(pair<const string, func>("minus", Minus_method));
    cal.insert(pair<const string, func>("multi", multi_method));
    cal.insert(pair<const string, func>("div", div_method));

    switcher.insert(pair<const string, cal_type>("add", cal_type::addop));
    switcher.insert(pair<const string, cal_type>("minus", cal_type::minusop));
    switcher.insert(pair<const string, cal_type>("multi", cal_type::multiop));
    switcher.insert(pair<const string, cal_type>("div", cal_type::divop));

    string ret;
    int first, second;
    cout << "Enter the method and the values" << endl;
    while (cin >> ret >> first >> second) {
        switch (switcher[ret])
        {
            case cal_type::addop:
                cout << cal[ret](first, second) << endl;
                break;
            case cal_type::minusop:
                cout << cal[ret](first, second) << endl;
                break;
            case cal_type::multiop:
                cout << cal[ret](first, second) << endl;
                break;
            case cal_type::divop:
                cout << cal[ret](first, second) << endl;
                break;
            default:
                cout << "No match operator" << endl;
                break;
        }
    }

    return 0;
}