编辑“︁C++unordered map”︁（章节）

== 实际应用案例 ==
=== 单词频率统计 ===
<syntaxhighlight lang="cpp">
#include <iostream>
#include <unordered_map>
#include <string>

void countWords(const std::string& text) {
    std::unordered_map<std::string, size_t> wordCount;
    std::string word;
    
    for (char c : text) {
        if (isalpha(c)) {
            word += tolower(c);
        } else if (!word.empty()) {
            ++wordCount[word];
            word.clear();
        }
    }
    
    if (!word.empty()) {
        ++wordCount[word];
    }
    
    // 输出结果
    for (const auto& pair : wordCount) {
        std::cout << pair.first << ": " << pair.second << '\n';
    }
}

int main() {
    std::string text = "Hello world hello c++ world";
    countWords(text);
    return 0;
}
</syntaxhighlight>

输出：
<pre>
hello: 2
world: 2
c: 1
</pre>

=== 缓存实现 ===
<syntaxhighlight lang="cpp">
#include <unordered_map>
#include <iostream>

template<typename Key, typename Value>
class SimpleCache {
private:
    std::unordered_map<Key, Value> cache;
    size_t maxSize;
    
public:
    SimpleCache(size_t size) : maxSize(size) {}
    
    bool get(const Key& key, Value& value) {
        auto it = cache.find(key);
        if (it != cache.end()) {
            value = it->second;
            return true;
        }
        return false;
    }
    
    void put(const Key& key, const Value& value) {
        if (cache.size() >= maxSize) {
            cache.erase(cache.begin());  // 简单策略：删除第一个元素
        }
        cache[key] = value;
    }
};

int main() {
    SimpleCache<std::string, int> cache(3);
    
    cache.put("one", 1);
    cache.put("two", 2);
    cache.put("three", 3);
    
    int value;
    if (cache.get("two", value)) {
        std::cout << "Found: " << value << '\n';
    }
    
    cache.put("four", 4);  // 这会淘汰"one"
    
    if (!cache.get("one", value)) {
        std::cout << "one was evicted from cache\n";
    }
    
    return 0;
}
</syntaxhighlight>

输出：
<pre>
Found: 2
one was evicted from cache
</pre>