C ++ unordered

C ++ unordered_map 如何区分空单元格与0(C++ unordered_map how to distinguish null cell from 0)

假设我有一个unordered_map<string, int> H

假设H中没有元素“house”，所以cout<<H["house"]; 会打印0。

但是假设我需要指定H["house"] = 0 。

如何区分不存在的元素和0的元素？

//example of what I want: if(!H["house"]){ cout<<"DOES NOT EXIST YET\n"; H["house"] = 0; } if(H["house"]){ cout<<"IT EXISTS NOW\n"; }

Suppose I have an unordered_map<string, int> H.

Let's say there is no element "house" in H, so cout<<H["house"]; would print 0.

But suppose I need to assign H["house"] = 0.

How would I distinguish an element that doesn't exist from one that is 0?

//example of what I want: if(!H["house"]){ cout<<"DOES NOT EXIST YET\n"; H["house"] = 0; } if(H["house"]){ cout<<"IT EXISTS NOW\n"; }

最满意答案

最短的测试：

if (H.count("house")) { // "house" exists } else { // "house" does not exist in H }

The shortest test:

if (H.count("house")) { // "house" exists } else { // "house" does not exist in H }