如何在map中按键删除元素，其中包含char和pair<int，string>

How to delete elements by key in map, which contains char and pair<int,string>

本文关键字：gt pair string char lt int map 元素 删除 包含      更新时间：2023-10-16

我要删除所有先配对的元素== 0

下面代码:

int main()
{
    map<char, pair<int,string>> myMap;
    map<char, pair<int,string>>::const_iterator it;
    for (int i = 0; i < 10; i++)
    {
        char c = 'a' + i;
        pair<int,string> p = make_pair(rand() % 2, "dd");
        myMap.insert(make_pair(c,p));
    }
    it = find_if(myMap.begin, myMap.end(), isEqual);
}
bool isEqual(const pair<char, pair<int, string> > element)
{
    return element.second.first == 0;
}
错误:

/usr/include/c++/4.8/bits/stl_algorithm .h:150: error: could not convert' __first.std::_Rb_tree_iterator<_Tp>::operator*<std::pair<const char, std::pair<int, std::basic_string<char> > > >() '从' std::pair<const char, std::pair<int, std::basic_string<char> > > '到' std::pair<int, std::basic_string<char> > '

   while (__first != __last && !bool(__pred(*__first)))

当然可以。

我想我会这样写代码(我添加了一些额外的代码来打印出删除前后的映射内容，以表明它有效):

#include <map>
#include <utility>
#include <iostream>
#include <stdlib.h>
#include <string>
#include <algorithm>
#include <iterator>
#include <vector>
using namespace std;
ostream &operator<<(ostream &os, pair<int, string> const &p) {
    return os << "[" << p.first << ", " << p.second << "]";
}
int main() {
    map<char, pair<int, string>> myMap;
    for (int i = 0; i < 10; i++) {
        char c = 'a' + i;
        pair<int, string> p = make_pair(rand() % 2, "dd");
        myMap.insert(make_pair(c, p));
    }
    std::cout << "before:n";
    for (auto const &p : myMap)
        std::cout << p.first << ": " << p.second << "n";
    map<char, pair<int, string> >::iterator it;
    while (myMap.end() != (it = find_if(myMap.begin(), myMap.end(), [](auto p) { return p.second.first == 0; })))
        myMap.erase(it);
    std::cout << "nafternn";
    for (auto const &p : myMap)
        std::cout << p.first << ": " << p.second << "n";
}

我将使用一个简单的循环来实现这一点。当从map中擦除元素时，需要记住跟踪迭代器:

#include <map>
#include <ctime>
#include <string>
#include <vector>
#include <cstdlib>
#include <iostream>
#include <algorithm>
int main()
{
    std::srand(std::time(0));
    std::map<char, std::pair<int, std::string>> myMap;
    for(int i = 0; i < 10; i++)
    {
        char c = 'a' + i;
        auto p = std::make_pair(rand() % 2, "dd");
        myMap.insert(std::make_pair(c, p));
    }
    std::cout << "nbefore:n";
    for(auto const& p: myMap)
    {
        std::cout << p.first;
        std::cout << " {" << p.second.first;
        std::cout << ", " << p.second.second;
        std::cout << "}" << 'n';
    }
    // remove items in a simple loop
    for(auto iter = myMap.begin(); iter != myMap.end();)
    {
        if(iter->second.first == 0)
            iter = myMap.erase(iter); // grab new iterator when erasing
        else
            ++iter; // otherwise just increment
    }
    std::cout << "nafter:n";
    for(auto const& p: myMap)
    {
        std::cout << p.first;
        std::cout << " {" << p.second.first;
        std::cout << ", " << p.second.second;
        std::cout << "}" << 'n';
    }
}

示例输出:

before:
a {0, dd}
b {1, dd}
c {0, dd}
d {0, dd}
e {1, dd}
f {0, dd}
g {0, dd}
h {1, dd}
i {0, dd}
j {0, dd}
after:
b {1, dd}
e {1, dd}
h {1, dd}
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