c++ unordered_map的count

unordered_map是C++ STL中的一个关联容器，用于存储键值对。count函数用于返回指定键在容器中出现的次数，因为unordered_map中每个键都是唯一的，所以count函数返回值只能是0或1。

示例代码：

#include <iostream>
#include <unordered_map>

int main() {
    std::unordered_map<std::string, int> myMap = {{"apple", 1}, {"banana", 2}, {"orange", 3}};

    // 判断键是否存在
    if (myMap.count("apple")) {
        std::cout << "apple exists in myMap" << std::endl;
    } else {
        std::cout << "apple does not exist in myMap" << std::endl;
    }

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

    return 0;
}

输出：

apple exists in myMap
pear does not exist in myMap