如何在C ++中使用find（itr，itr，const tp）算法和map [英] How to use find(itr ,itr ,const tp) algorithm with map in C++

问题描述

我想知道如何使用地图查找（itr，itr，key）。此代码与我一起生成错误消息。

Hi, I was wondering how to use find(itr,itr,key) with a map. This code generates an error message with me.

#include <iostream>
#include <string>
#include <algorithm>
#include <map>

using namespace std;

int main()
{
    map<string, string> student_roster;
    student_roster.insert(pair<string,string>("John","a"));
    map<string, string>::iterator itr;
    itr = find( student_roster.begin() , student_roster.end() , "John" );//the error
    if (itr == student_roster.end())
        cerr << "John is not found" << endl;
    else
        cout << "Student : " << itr->first << " Grade : " << itr->second << endl;
}

然而，使用该算法是不合法的吗？



谢谢，山姆。

However, is it not legal to use that algorithm ?

Thanks, Sam.

推荐答案

您正在使用 std :: find [ ^ ]。这是一种适用于任何容器的通用算法，但它不了解容器元素的属性。地图的元素是（键，值）对，而不是字符串。因此，find无法将元素与您传递的字符串作为搜索值进行比较。它需要一个运算符来比较一个不存在的map元素类型和字符串。

You are using std::find[^]. This is a generic algorithm that works for any container, but it has no knowledge of the properties of the elements of the container. The elements of a map are (key,value) pairs, not strings. Therefore, find fails to compare the elements with the string you pass as the search value. It would need an operator to compare a map element type to string, which doesn't exist.

你没有正确使用find。请看下面

You are not using find correctly. Please see below

itr = student_roster.find( "John" );

这篇关于如何在C ++中使用find（itr，itr，const tp）算法和map的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！