c++ - std::find on map 无法正常运行并遍历 map 的键和值

Question

我目前正在尝试访问我的 map 的特定值元素并遍历 map 以打印我的 map 的所有键及其特定元素但是当我在我的 IDE (Eclipse) 上调试时遇到错误关于如何我能战胜这场斗争吗？过去几天一直在寻找答案。

当调用 std::find 时，它说，

'no matching member function for call to 'find'

当通过映射使用迭代器到迭代器时，它说，

invalid operands to binary expression ('ostream' (aka 'basic_ostream') and 'const std::__1::vector >')

#include <iostream>
#include <vector>
#include <map>
#include <iterator>
#include <algorithm>
using namespace std;

int main() {
    srand(time(NULL));

    cout << "Enter # of rows: ";
    int row;
    cin >> row;
    cout << "Enter # of columns: ";
    int column;
    cin >> column;

    vector<vector<int> > numberBoard;

    int startingIndex = 1;
    for(int i = 0; i < row; i++){
        vector<int> temp;
        for(int j = 0; j < column; j++){
            temp.push_back(startingIndex);
            startingIndex++;
        }
        numberBoard.push_back(temp);
    }

    cout <<"Number Board:" << endl;
    for(int i = 0; i < numberBoard.size(); i++){
        for(int j = 0; j < numberBoard[i].size(); j++){
            cout.width(5);
            cout << numberBoard[i][j];
        }
        cout << endl;
    }

        vector<vector<char> > hiddenBoard(row, vector<char>(column));

        // looping through outer vector vec
        for (int i = 0; i < row; i++) {
          // looping through inner vector vec[i]
          for (int j = 0; j < column; j++) {
              int random = rand()% 32 + 65;
            (hiddenBoard[i])[j] = char(random);
            //i*n + j;
          }
        }

        cout << "\nBoard:" << endl;
        for(int i = 0; i < hiddenBoard.size(); i++){
            for(int j = 0; j < hiddenBoard[i].size(); j++){
                cout.width(5);
                cout << hiddenBoard[i][j];
            }
            cout << endl;
        }
        map<vector<int>, vector<char> > boardMap;
        for(int i = 0; i < 20; i++){
                boardMap[numberBoard[i]] = hiddenBoard[i];
        }

        //using std::find
        int slotNum = 3;
        map<vector<int>, vector<char> >::iterator it = boardMap.find(slotNum);

        //trying to iterate through the map to print its corresponding key and value.
        for(map<vector<int>, vector<char> >::iterator it = boardMap.begin(); it != boardMap.end(); it++){
                cout << it->first << " => " << it->second << endl;
        }

    return 0;
}

Answer 1

首先，我很想知道您的程序应该做什么，这需要一个将整数 vector 映射到字符 vector 的映射。该映射存储成对的 int vector 和 char vector ，例如:

3 8 5 7 => c j i e
5 7 2 0 => l o x w
1 4 3 8 => k r u a

也许你想要一个 std::map<int, char>它将一个 int 映射到一个 char，例如:

5 => m
2 => c
0 => a

如果你想打印出 std::map<std::vector<int>, std::vector<char>> 的内容，你需要像你已经在做的那样迭代键值对，然后用循环分别打印出键 vector 和值 vector 。

例子:

#include <iostream>
#include <map>
#include <vector>

int main()
{
    std::map<std::vector<int>, std::vector<char>> boardMap; //declare and insert some values for testing
    boardMap.insert(std::make_pair(std::vector<int>({ 8, 6, 2, 7 }), std::vector<char>({ 'o', 'd', 'a' })));
    boardMap.insert(std::make_pair(std::vector<int>({ 4, 1, 0, 4 }), std::vector<char>({ 's', 'd', 'l' })));

    for (auto it = boardMap.begin(); it != boardMap.end(); ++it)
    { //using auto is much better than writing std::map<std::vector<int>, std::vector<char>>::iterator every time
        for (auto vecIt = it->first.begin(); vecIt != it->first.end(); ++vecIt) //output key vector
        {
            std::cout << *vecIt << ' ';
        }
        std::cout << "=>";
        for (auto vecIt = it->second.begin(); vecIt != it->second.end(); ++vecIt) //output value vector
        {
            std::cout << ' ' << *vecIt;
        }
        std::cout << '\n';
    }
    return 0;
}

带有范围 for 循环的更优雅的版本:

#include <iostream>
#include <map>
#include <vector>

int main()
{
    std::map<std::vector<int>, std::vector<char>> boardMap; //declare and insert some values for testing
    boardMap.insert(std::make_pair(std::vector<int>({ 8, 6, 2, 7 }), std::vector<char>({ 'o', 'd', 'a' })));
    boardMap.insert(std::make_pair(std::vector<int>({ 4, 1, 0, 4 }), std::vector<char>({ 's', 'd', 'l' })));

    for (auto &keyValuePair : boardMap)
    { //using auto is much better than writing std::map<std::vector<int>, std::vector<char>>::iterator every time
        for (auto &keyNum : keyValuePair.first) //output key vector
        {
            std::cout << keyNum << ' ';
        }
        std::cout << "=>";
        for (auto &valueNum : keyValuePair.second) //output value vector
        {
            std::cout << ' ' << valueNum;
        }
        std::cout << '\n';
    }
    return 0;
}

尽管最好的方法是使用 <algorithm> 中的函数标题如 std::for_each 和 lambdas 为你做所有的循环。不过我不擅长这些。

对于您的查找操作，您有一张 map std::vector<int>作为键，但你给 std::map::find 一个整数功能。如果你真的想要一个以 vector 作为键的映射，你需要给函数一个 vector ，比如:

auto findResult = boardMap.find(std::vector<int>({8, 5, 2, 6}));

这构建了一个包含四个数字的 vector 并将其提供给 std::map::find .