面对过程

• vector<>来存输入文件的每一行
• map<string,set<int>>,每一个单词映射一个集合,集合包含其出现的行数
• istringstream:将每一行string放到字符串流里面,通过流来分割出单词,

   1 #include <iostream>
   2 #include <sstream>
   3 #include <fstream>
   4 #include <vector>
   5 #include <set>
   6 #include <map>
   7 #include <string>
   8 
   9 #include <cstdlib>
  10 using namespace std;
  11 using line_no = vector<string>::size_type;
  12 vector<string> file;
  13 map<string,set<line_no>> wm;
  14 
  15 string cleanup_str(const string& word) {
  16     string ret;
  17     for (auto it = word.begin(); it!=word.end(); it++) {
  18         if (!ispunct(*it))
  19             ret += tolower(*it);
  20     }
  21     return ret;
  22 }
  23 
  24 ostream& query_and_print(const string& sought,ostream& os) {
  25     auto loc = wm.find(sought);
  26     if (loc == wm.end()) {
  27         os << sought << " have seen zero times " << endl;
  28     } else {
  29         // loc is a iterator , and pair<> is being pointed
  30         auto lines = loc->second;
  31         os << sought << "have seen " << lines.size() << " times " << endl;
  32         for (auto num : lines)                                                   
  33             os << "\t (The " << num+1 << " line) " << *(file.begin() + num) << e#
  34     }
  35     return os;
  36 }
  37 
  38 void input_txt(ifstream& is) {
  39     string text;
  40     while (getline(is,text)) {
  41         file.push_back(text);
  42         int n = file.size() - 1;
  43         istringstream line(text);
  44         string word;                                                             
  45         while (line >> word)
  46             wm[cleanup_str(word)].insert(n);
  47         }
  48 }
  49 void runQueries(ifstream& infile) {
  50     input_txt(infile);
  51     while (true) {
  52         cout << "Enter word to look for, or q to quit: ";
  53         string s;
  54         if (!(cin >> s) || s == "q") break;
  55         query_and_print(s,cout);
  56     }
  57 }
  58 int main() {
  59     ifstream infile("1.in");
  60     if (!infile) {
  61         cout << " fail to open infile ";
  62         return -1;
  63     }
  64     runQueries(infile);
  65     infile.close();
  66     return 0;
  67 }

关于&是否会增加shared_ptr<>的引用计数问题

• 变量的引用只是变量的别名,并不会增加智能指针的引用计数

   1 #include <iostream>
   2 #include <memory>
   3 using namespace std;
   4 
   5 int main() {
   6     shared_ptr<int> p (new int(24));
   7     cout << p.use_count() << endl;
   8 
   9     auto& q = p;                                                                 
  10     cout << " q.use_count()= " << q.use_count() << " *q= " << *q << endl;
  11     cout << " p.use_coutn()= " << p.use_count() << " *p= " << *p << endl;
  12     return 0;
  13 }

• 创建了一个新的shared_ptr<>对象并且指向同一块内存,自然就会增加shared_ptr的引用计数

   1 #include <iostream>
   2 #include <memory>
   3 using namespace std;
   4 
   5 int main() {
   6     shared_ptr<int> p (new int(24));
   7     cout << p.use_count() << endl;
   8 
   9     auto q = p;                                                                  
  10     cout << " q.use_count()= " << q.use_count() << " *q= " << *q << endl;
  11     cout << " p.use_coutn()= " << p.use_count() << " *p= " << *p << endl;
  12     return 0;
  13 }

  面对对象

  // 注意使用指针和对象之间的区别
  #include <iostream>
  #include <fstream>
  #include <sstream>
  #include <string>
  #include <vector>
  #include <map>
  #include <set>
  #include <memory>
  using namespace std;
  //QueryResult 保存查询结果的类,要想共享类之间的数据且不通过拷贝,shared_ptr<>来解决
  class QueryResult;
  class TextQuery {
  public:
  	using line_no = vector<string>::size_type; //类型成员
  	TextQuery(ifstream&); //接收 文件流来读取文本
  	QueryResult query(const string&) const; // 
  private:
  	shared_ptr<vector<string>> file;
  	map<string, shared_ptr<set<line_no>>> wm; //string 关联一个 动态分配的set<>集合
  };
  TextQuery::TextQuery(ifstream& in):file(new vector<string>){
  	string text;
  	while (getline(in,text)) {
  		(*file).push_back(text);
  		int n = (*file).size() - 1;
  		istringstream line(text);
  		string word;
  		while (line >> word) {
  			// wm[word] 是一个shared_ptr<set<line_no>>指针,但是我们不确定他是否分配了内存
  			auto& lines = wm[word]; //& 不增加 引用计数
  			if (!lines) //如果 智能指针为空,.reset(新动态内存对象)
  				lines.reset(new set<line_no>);
  			(*lines).insert(n);
  		}
  	}
  }
  class QueryResult {
  	friend ostream& print(ostream&,const QueryResult&); //友元
  public:
  	using line_no = vector<string>::size_type;
  	QueryResult(string s, shared_ptr<set<line_no>> p, shared_ptr<vector<string>> f) :sought(s), lines(p), file(f) {}
  private:
  	// 查询结果3内容
  	string sought;
  	shared_ptr<set<line_no>> lines;
  	shared_ptr<vector<string>> file;
  };
  QueryResult TextQuery::query(const string& sought) const{
  	//如果 没有找到该单词所属的行,返回一个指向空set的shared_ptr,static(全局静态)保证了函数结束前内存不会被释放
  	static shared_ptr<set<line_no>> nodata(new set<line_no>);
  	auto loc = wm.find(sought);
  	if (loc == wm.end())
  		//将TextQuery的内存也让QueryResult的shared_ptr指向,这样就能共享内存，
  		return QueryResult(sought, nodata, file);
  	else
  		return QueryResult(sought,loc->second,file);
  }
  ostream& print(ostream& os, const QueryResult& qr) { //接收一个查询结果类
  	os << qr.sought << " occurs " << qr.lines->size() << " times " << endl;
  	for (auto num : *qr.lines)
  		os << "\t(line " << num + 1 << ")  " << *(qr.file->begin() + num) << endl;
  	return os;
  }
  int main() {
  	ifstream in("a.txt");
  	if (!in) { //文件打开失败,return 
  		cout << "fail to open file " << endl;
  		return -1;
  	}
  	TextQuery solution(in); //传入输入流对象初始化
  	while (1) {
  		cout << " Enter word to look for, or q to quit: ";
  		string s;
  		if (!(cin >> s) || s == "q") break;
  		print(cout,solution.query(s)); //querys返回一个QueryResult对象
  	}
  	return 0;
  }