如何在 C++ 中按字母順序輸出特定 Map 值的鍵？

Question

我正在嘗試打印出特定映射值的內容，但是根據括號內的字母按字母順序排列。

下面是不符合我想要做的原始輸出。

 | Element [ab] Element 2 Element [a] Element 1 Element [b] Element 3 Element [e] Element 6 Element [d] Element 5 Element [c] Element 4 |

現在我試圖得到的輸出如下，它將使用 printSelectiveAlphabetic() 函數

 | Element [a] Element 1 Element [ab] Element 2 Element [b] Element 3 Element [c] Element 4 Element [d] Element 5 Element [e] Element 6 |

那么如何調整我的 printSelectiveAlphabetic() 函數以獲得所需的輸出？

下面的代碼：

#include <iostream>
#include <string>
#include <vector>
#include <list>
#include <algorithm>
#include <iterator>
#include <sstream>
#include <map>

using namespace std;

//Prints whole map
void printMap(map<string, vector<string>>  mapVar) {
    cout << endl;
    map<string ,vector<string>> :: iterator it;
    for(it=mapVar.begin();it !=mapVar.end();++it)
      {
       cout << it->first << endl;
       for(auto it2 = it->second.begin(); it2 != it->second.end(); ++it2) {
            cout << *it2 << " ";
            cout << endl;}
      }
}

//Prints specific value of map
void printSelectiveMap(vector<string> v, map<string, vector<string>> helpMap) {
    cout << "\t|"<<endl;
    string searchValue = v[0];
        for (auto map_iter = helpMap.cbegin(); map_iter != helpMap.cend(); ++map_iter) {
            if (v[0] == map_iter->first) {
                    int count = 0;
                    for (auto vec_iter = map_iter->second.cbegin(); vec_iter != map_iter->second.cend(); ++vec_iter) {
                            cout << "\t" << searchValue << " " << *vec_iter << endl;
                }
            }
        }
    cout << "\t|"<<endl;
}

//A copy of the above function, what I'm trying to change to have alaphabetical output
//This needs to use the letters, not the numbers in the vector to implement this
void printSelectiveAlphabetic(vector<string> v, map<string, vector<string>> helpMap) {
    cout << "\t|"<<endl;
    string searchValue = v[0];
        for (auto map_iter = helpMap.cbegin(); map_iter != helpMap.cend(); ++map_iter) {
            if (v[0] == map_iter->first) {
                    int count = 0;
                    for (auto vec_iter = map_iter->second.cbegin(); vec_iter != map_iter->second.cend(); ++vec_iter) {
                            cout << "\t" << searchValue << " " << *vec_iter << endl;
                }
            }
        }
    cout << "\t|"<<endl;
}

int main() {

    map<string, vector<string>> maphelp;

    vector<string> vect;
    vect.push_back("[ab] Element 2");
    vect.push_back("[a] Element 1");
    vect.push_back("[b] Element 3");
    vect.push_back("[e] Element 6");
    vect.push_back("[d] Element 5");
    vect.push_back("[c] Element 4");
    maphelp.insert(pair<string,vector<string>>("Element", vect));

    cout << endl;
    vector<string> vect1;
    vect.push_back("[ab] Element1 2");
    vect1.push_back("[a] Element1 1");
    vect1.push_back("[b] Element1 3");
    vect1.push_back("[e] Element1 6");
    vect1.push_back("[d] Element1 5");
    vect1.push_back("[c] Element1 4");
    maphelp.insert(pair<string,vector<string>>("Element1", vect1));

    cout << "-------------------" << endl;
    cout << "This output is not part of the question." << endl;
    cout << "These are just printed variables below for reference:" << endl;
    cout << endl;

    cout << "Entire map printed.";
    printMap(maphelp);
    cout << endl;


    vector<string> v;
    v.push_back("Element");
    cout << "Selective value of map to be printed: " << v[0] << endl;

    cout << "-------------------" << endl;
    cout << endl;

    cout << "Now below is the original output which doesn't meet what I'm trying to do." << endl;
    printSelectiveMap(v, maphelp);
    cout << endl;
    cout << "Now the output I'm trying to get is below, which would be using the printSelectiveAlphabetic() function" << endl;

    //function I'm trying to adjust
    //PrintSelectiveAlphabetic()

    cout << "\t|"<<endl;
    cout << "\tElement [a] Element 1" << endl;
    cout << "\tElement [ab] Element 2" << endl;
    cout << "\tElement [b] Element 3" << endl;
    cout << "\tElement [c] Element 4" << endl;
    cout << "\tElement [d] Element 5" << endl;
    cout << "\tElement [e] Element 6" << endl;
    cout << "\t|"<<endl;
    cout << "-------------------" << endl;
    cout<<endl;
    cout << "So how do I adjust my printSelectiveAlphabetic() function to get this desired output?"<< endl;
}

Answer 1

最簡單的方法是使用std::sort對與v[0]對應的向量進行排序，以實現您的預​​期輸出，如下所示：

void printSelectiveAlphabetic(vector<string> v, map<string, vector<string>> helpMap) {
    cout << "\t|"<<endl;
    
    std::sort(helpMap.at(v[0]).begin(), helpMap.at(v[0]).end()); //sort the vector corresponding to the key v[0]
    for(const std::string& element: helpMap[v[0]])
    {
        std::cout<<v[0] <<" "<<element<<std::endl;
    }
    cout << "\t|"<<endl;
}

上述程序的輸出是：

        |
Element [a] Element 1
Element [ab] Element 2
Element [b] Element 3
Element [c] Element 4
Element [d] Element 5
Element [e] Element 6
        |

工作演示