Question

我想知道是否存在简化for循环的方法，例如lambda表达式，而无需更改下面代码的性质。如果可能的话，我还想知道是否还有其他方法（更好）来执行一系列功能，这些功能可以完成类似下面的代码的操作。谢谢

#include <iostream>
#include <functional>
#include <vector>
using namespace std;
void turn_left(){  // left turn function
    cout<<"Turn left"<<endl;
}
void turn_right(){ // right turn function
    cout<<"Turn right"<<endl;
}
void onward(){  // moving forward function
    cout<<"Onward"<<endl;
}
int main() {
    vector<char>commands{'L', 'R', 'M'}; // commmands (keys)for robot to turn or move;
    vector<pair<function<void()>, char>> actions; // a vector of pairs, which pairs up the function pointers with the chars;
    actions.push_back(make_pair(turn_left, 'L')); //populate the vector actions
    actions.push_back(make_pair(turn_right, 'R'));
    actions.push_back(make_pair(onward, 'M'));
    for (int i =0; i<commands.size();++i){
        if(commands.at(i)==actions.at(i).second){
            actions.at(i).first();
        }
    }
}

Answer 1

您可以使用std::map / std::unordered_map来将函数映射到命令，而不是使用lambda来简化代码，然后可以使用基于范围的for循环遍历所有对象您所拥有的命令。

int main() {
    vector<char>commands{'L', 'R', 'M'}; // commmands (keys)for robot to turn or move;
    std::map<char, function<void()>> actions = {{'L', turn_left},{'R', turn_right},{'M', onward}};
    for (auto command : commands)
        actions[command]();
}

Answer 2

我将添加一个函数来执行命令，然后从循环中调用它：

#include <iostream>
#include <functional>
#include <vector>
using namespace std;
void turn_left(){  // left turn function
    cout<<"Turn left"<<endl;
}
void turn_right(){ // right turn function
    cout<<"Turn right"<<endl;
}
void onward(){  // moving forward function
    cout<<"Onward"<<endl;
}

// The next step is to put actions/executeAction() into a class.
vector<pair<char, function<void()>>> actions; // a vector of pairs, which pairs up the function pointers with the chars;

void executeAction(char command)
{
    auto find = actions.find(command);
    if (find != actions.end()) {
        find->second();
    }
}

int main() {
    vector<char>commands{'L', 'R', 'M'}; // commmands (keys)for robot to turn or move;

    actions.push_back(make_pair('L', turn_left)); //populate the vector actions
    actions.push_back(make_pair('R', turn_right));
    actions.push_back(make_pair('M', onward));

    for (auto c: commands){
        executeAction(c);
    }
}

我可以使用Lambda简化for循环

2 个答案: