c++ map的count

C++中的map是一种关联容器，它将键映射到值。count()函数用于返回指定键在map中出现的次数，因为map中每个键只能出现一次，所以count()函数的返回值只能是0或1。

例如，我们有一个map<string, int>，我们可以使用count()函数来检查某个键是否存在于map中：

#include <iostream>
#include <map>
using namespace std;

int main() {
    map<string, int> myMap;
    myMap["apple"] = 1;
    myMap["banana"] = 2;
    myMap["orange"] = 3;

    if (myMap.count("apple")) {
        cout << "apple exists in the map" << endl;
    } else {
        cout << "apple does not exist in the map" << endl;
    }

    if (myMap.count("pear")) {
        cout << "pear exists in the map" << endl;
    } else {
        cout << "pear does not exist in the map" << endl;
    }

    return 0;
}

输出结果为：

apple exists in the map
pear does not exist in the map