C++ 搜索引擎 Searcher 模块源码解析：正倒排索引实现

3. GetDesc

此函数负责生成摘要，即在 HTML 内容中查找是否出现关键词。若找到，截取关键词前后指定长度的内容；若未找到或长度不足，则返回空值。边界检查防止越界访问。

std::string GetDesc(const std::string& html_content, const std::string& word) {
    int prev_step = 50;
    int next_step = 100;
    
    // 在 html_content 中查找 word，忽略大小写
    auto iter = std::search(html_content.begin(), html_content.end(), word.begin(), word.end(),
                            [](int x, int y) { return (std::tolower(x) == std::tolower(y)); });
    
    if (iter == html_content.end()) return "None1";
    int pos = std::distance(html_content.begin(), iter);
    
    if (pos == std::string::npos) return "None1";
    
    int start = 0;
    int end = html_content.size() - 1;
    
    if (pos - prev_step > start) start = pos - prev_step;
    if (pos + next_step < end) end = pos + next_step;
    
    if (start >= end) return "None2";
    
    std::string desc = html_content.substr(start, end - start);
    desc += "...";
    return desc;
}

4. InvertedElemPrint

该结构体用于解决文档重复问题。作为'去重与信息聚合'的载体，当同一文档匹配多个关键词时，借助哈希表的键唯一性，避免文档在结果中重复出现。

struct InvertedElemPrint {
    uint64_t doc_id;
    int weight;
    std::vector<std::string> words;
    InvertedElemPrint() : doc_id(0), weight(0) {}
};

5. 完整源码参考

通过'索引构建'提前做好数据准备，通过'查询处理'高效匹配并排序文档，通过'结果格式化'衔接前端展示，最终实现'用户输入关键词→得到清晰搜索结果'的完整功能。

#pragma once
#include "index.hpp"
#include "usuallytool.hpp"
#include <algorithm>
#include <jsoncpp/json/json.h>
#include "log.hpp"

namespace ns_searcher {

struct InvertedElemPrint {
    uint64_t doc_id;
    int weight;
    std::vector<std::string> words;
    InvertedElemPrint() : doc_id(0), weight(0) {}
};

class Searcher {
private:
    ns_index::Index* index;
public:
    Searcher() {}
    ~Searcher() {}

public:
    void InitSearcher(const std::string& input) {
        index = ns_index::Index::GetInstance();
        index->BuildIndex(input);
        LOG1(NORMAL, "建立索引成功...");
    }

    void Search(const std::string& query, std::string* json_string) {
        std::vector<std::string> words;
        ns_util::JiebaUtil::CutString(query, &words);

        std::vector<InvertedElemPrint> inverted_list_all;
        std::unordered_map<uint64_t, InvertedElemPrint> tokens_map;

        for (std::string w : words) {
            boost::to_lower(w);
            ns_index::InvertedList* inverted_list = index->GetInvertedList(w);
            if (inverted_list == nullptr) continue;

            for (const auto& elem : *inverted_list) {
                auto& item = tokens_map[elem.doc_id];
                item.doc_id = elem.doc_id;
                item.weight += elem.weight;
                item.words.push_back(elem.word);
            }
        }

        for (const auto& item : tokens_map)
            inverted_list_all.push_back(std::move(item.second));

        std::sort(inverted_list_all.begin(), inverted_list_all.end(),
                  [](const InvertedElemPrint& e1, const InvertedElemPrint& e2) {
                      return e1.weight > e2.weight;
                  });

        Json::Value root;
        for (auto& item : inverted_list_all) {
            ns_index::DocInfo* doc = index->GetForwardIndex(item.doc_id);
            if (doc == nullptr) continue;
            Json::Value elem;
            elem["title"] = doc->title;
            elem["desc"] = GetDesc(doc->content, item.words[0]);
            elem["url"] = doc->url;
            root.append(elem);
        }

        Json::StyledWriter writer;
        *json_string = writer.write(root);
    }

    std::string GetDesc(const std::string& html_content, const std::string& word) {
        int prev_step = 50;
        int next_step = 100;
        auto iter = std::search(html_content.begin(), html_content.end(), word.begin(), word.end(),
                                [](int x, int y) { return (std::tolower(x) == std::tolower(y)); });
        if (iter == html_content.end()) return "None1";
        int pos = std::distance(html_content.begin(), iter);
        if (pos == std::string::npos) return "None1";
        int start = 0;
        int end = html_content.size() - 1;
        if (pos - prev_step > start) start = pos - prev_step;
        if (pos + next_step < end) end = pos + next_step;
        if (start >= end) return "None2";
        std::string desc = html_content.substr(start, end - start);
        desc += "...";
        return desc;
    }
};
}