c/c++ 继承与多态 文本查询的小例子（非智能指针版本）

问题：在上一篇继承与多态 文本查询的小例子（智能指针版本）在Query类里使用的是智能指针，只把智能指针换成普通的指针，并不添加拷贝构造方法，会发生什么呢？

执行时，代码崩掉。

分析下面一行代码:

Query qb = ~Query("Alice");

1，首先调用Query(string)的构造函数，把Query的成员q指向了new WordQuery(s)

Query::Query(const std::string& s) : q(new WordQuery(s)){std::cout << "Query pub" << std::endl;
}

2，调用WordQuery的构造函数

3，调用重载的operator~方法，参数是在1处的Query的无名的临时对象

inline Query operator~(const Query& op){//return std::shared_ptr<Query_base>(new NotQuery(op));std::shared_ptr<Query_base> tmp(new NotQuery(op));return Query(tmp);
}

4，调用NotQuery的构造方法，参数是在1处的Query的无名的临时对象。query(q)是调用了Query的合成的拷贝构造方法，所以NotQuery的私有成员query和1处的Query的无名的临时对象的成员q都指向了在2处构建的WordQuery的对象。

NotQuery(const Query& q):query(q){std::cout << "NotQuery" << std::endl;
}

5，return Query(tmp);调用了Query的构造函数，又做出了一个Query对象。这个Query的q成员指向了在4处做成的NotQuery对象，这个NotQuery对象的query成员的q成员指向了在2处做成的WordQuery对象。

Query(Query_base* qb):q(qb){}

6，把在5处做成的Query对象，给qb【Query qb = ~Query("Alice");】，这个时点，在1处的Query的无名的临时对象，已经没有用了，就会释放它，就会调用Query的析构函数，析构函数会delete p；这个p指向的是2处的WordQuery。

接下来执行：

  print(std::cout, qb.eval(tq)) << std::endl;

这时qb的q指向的是4处NotQuery，4处的NotQuery的query的q，也是指向2处的WordQuery。这时qb去调用eval方法时，用qb里的q指向的NotQuery调用eval，然后用NotQuery里query的q去调用WorQuery的eval方法，可是NotQuery里query的q指向的2处的WordQuery已经被释放，程序就蹦了（segment core error）。

怎么解决？ 自定义拷贝构造函数。

Query.h

#ifndef __QUERY_H__
#define __QUERY_H__#include <string>
//#include <memory>
#include <iostream>
#include "TextQuery.h"class QueryResult;
class Query;class Query_base{friend class Query;protected:using line_no = TextQuery::line_no;virtual ~Query_base() = default;private:virtual QueryResult eval(const TextQuery&) const = 0;virtual std::string rep() const = 0;virtual Query_base* clone() const = 0;
};class Query{friend Query operator~(const Query&);//需要访问私有的构造函数friend Query operator|(const Query&, const Query&);//需要访问私有的构造函数friend Query operator&(const Query&, const Query&);//需要访问私有的构造函数public:Query(const std::string&);//构建一个新的WordQuery~Query(){std::cout << "Free" << std::endl;delete q;}Query(const Query& tmp){if(&tmp != this){std::cout << "copy Query" << std::endl;q = tmp.q->clone();}}Query& operator=(const Query& tmp){std::cout << "= Query" << std::endl;}// 接口函数：调用对应的Query_base操作QueryResult eval(const TextQuery& t) const{return q->eval(t);}std::string rep()const{return q->rep();}private:/*Query(std::shared_ptr<Query_base> query):q(query){std::cout << "Query pri:" << std::endl;}*/Query(Query_base* qb):q(qb){}Query_base* q;};class WordQuery : public Query_base{friend class Query;//Query 使用WordQuery的私有构造函数WordQuery(const std::string& s): query_word(s){std::cout << "WordQuery:" << s << std::endl;}QueryResult eval(const TextQuery& t)const{return t.query(query_word);}std::string rep()const{return query_word;}virtual WordQuery* clone() const {return new WordQuery(*this);}std::string query_word;
};class NotQuery : public Query_base{friend Query operator~(const Query&);NotQuery(const Query& q):query(q){//调用Query的拷贝构造函数std::cout << "NotQuery" << std::endl;}std::string rep() const {return "~(" + query.rep() + ")";}virtual NotQuery* clone() const {return new NotQuery(*this);}QueryResult eval(const TextQuery&)const;Query query;
};inline Query operator~(const Query& op){//return std::shared_ptr<Query_base>(new NotQuery(op));Query_base* tmp = new NotQuery(op);return Query(tmp);
}class BinaryQuery : public Query_base{protected:BinaryQuery(const Query& l, const Query& r,std::string s): lhs(l), rhs(r), opSym(s){std::cout << "BinaryQuery" << std::endl;}std::string rep() const {return "(" + lhs.rep() + " "+ opSym + " "+ rhs.rep() + ")";}Query lhs, rhs;std::string opSym;
};class AndQuery : public BinaryQuery{friend Query operator&(const Query&, const Query&);AndQuery(const Query& l, const Query& r): BinaryQuery(l, r, "&"){std::cout << "AndQuery" << std::endl;}QueryResult eval(const TextQuery&) const;virtual AndQuery* clone() const {return new AndQuery(*this);}
};inline Query operator&(const Query& lhs, const Query& rhs){return new AndQuery(lhs, rhs);
}class OrQuery : public BinaryQuery{friend Query operator|(const Query&, const Query&);OrQuery(const Query& l, const Query& r): BinaryQuery(l, r, "|"){std::cout << "OrQuery" << std::endl;}virtual OrQuery* clone() const {return new OrQuery(*this);}QueryResult eval(const TextQuery&) const;
};inline Query operator|(const Query& lhs, const Query& rhs){return new OrQuery(lhs, rhs);
}#endif

Query.cpp

#include "Query.h"
#include <algorithm>
#include <memory>/*
std::ostream& operator<<(std::ostream& os, const Query& q){//Query::rep通过它的Query_base指针对rep()进行虚调用return os << q.rep();
}
*/
Query::Query(const std::string& s) : q(new WordQuery(s)){std::cout << "Query pub" << std::endl;
}QueryResult NotQuery::eval(const TextQuery& text)const{//通过Query运算对象对eval进行虚调用auto result = query.eval(text);//开始时结果set为空auto ret_lines = std::make_shared<std::set<line_no>>();auto beg = result.begin();auto end = result.end();//对于输入文件的每一行，如果该行不在result当中，则将其添加到ret_linesauto sz = result.get_file()->size();for(size_t n = 0; n != sz; ++n){//如果还没有处理完result的所以行//检查当前行是否存在if(beg == end || *beg != n){ret_lines->insert(n);}else if(beg != end){++beg;//继续获取reslut的下一行}}return QueryResult(rep(), ret_lines, result.get_file());
}QueryResult AndQuery::eval(const TextQuery& text)const{//通过Query成员lhs,rhs进行虚调用//调用eval返回每个对象的QueryResultauto right = rhs.eval(text);auto left  = lhs.eval(text);//保存left和right交集的setauto ret_lines =std::make_shared<std::set<line_no>>();//将两个范围的交集写入一个目的迭代其中。std::set_intersection(left.begin(), left.end(),right.begin(), right.end(),inserter(*ret_lines, ret_lines->begin()));return QueryResult(rep(), ret_lines, left.get_file());
}QueryResult OrQuery::eval(const TextQuery& text)const{//通过Query成员lhs,rhs进行虚调用//调用eval返回每个对象的QueryResultauto right = rhs.eval(text);auto left  = lhs.eval(text);//将左侧运算对象的行号拷贝到结果set中auto ret_lines =std::make_shared<std::set<line_no>>(left.begin(), left.end());//插入右侧运算对象所得的行号ret_lines->insert(right.begin(), right.end());//返回一个新的QueryResult，它表示lhs和rhs的并集return QueryResult(rep(), ret_lines, right.get_file());
}

QueryResult.h

#ifndef __QUERYRESULT_H__
#define __QUERYRESULT_H__#include <iostream>
#include <set>
#include <vector>
#include <string>
#include <memory>class QueryResult{friend std::ostream& print(std::ostream&, const QueryResult&);
public:using line_no = std::vector<std::string>::size_type;using Iter = std::set<line_no>::iterator;QueryResult(std::string s, std::shared_ptr<std::set<line_no>> p,std::shared_ptr<std::vector<std::string>> f):sought(s), lines(p), file(f){}Iter begin() const {return lines->begin();}Iter end() const {return lines->end();}std::shared_ptr<std::vector<std::string>> get_file() const{return file;}
private:std::string sought;//查询的单词                                                    std::shared_ptr<std::set<line_no>> lines;//出现的行号                                   std::shared_ptr<std::vector<std::string>> file;
};
//QueryResult类的友元声明
std::ostream& print(std::ostream&, const QueryResult&);#endif

TextQuery.h

#ifndef __TEXTQUERY_H__
#define __TEXTQUERY_H__#include "QueryResult.h"
#include <map>
#include <iostream>
#include <fstream>
#include <sstream>
#include <set>
#include <vector>
#include <string>
#include <memory>using namespace std;
class TextQuery{public:using line_no = std::vector<std::string>::size_type;TextQuery(ifstream& is);  QueryResult query(const std::string &sought) const;private:std::shared_ptr<std::vector<std::string>> file;std::map<std::string, std::shared_ptr<std::set<line_no>>> wm;
};#endif

TextQuery.cpp

#include "TextQuery.h"using namespace std;TextQuery::TextQuery(ifstream& is) : file(new vector<string>){string text;while(getline(is, text)){//读文件的每一行                                   file->push_back(text);int n = file->size() - 1;//当前行号                                       istringstream line(text);//将行文本分解为单词                             string word;while(line >> word){//非常重要，必须用引用，要不然就会拷贝一个新的set给lines，不是原来的    auto &lines = wm[word];//lines是shared_ptr                              if(!lines)lines.reset(new set<line_no>);lines->insert(n);}}
}QueryResult TextQuery::query(const string &sought) const{//如果没有找到sought，返回指向此set的一个智能指针                           static shared_ptr<set<line_no>> nodata(new set<line_no>);auto ret = wm.find(sought);if(ret == wm.end()){return QueryResult(sought, nodata, file);//没有找到                       }else{return QueryResult(sought, ret->second, file);}
}

main.cpp

#include "Query.h"//QueryResult的友元函数                                                         
ostream& print(ostream& os, const QueryResult& qr){os << qr.sought << " 出现了：" << qr.lines->size() << "次" << endl;for(auto num : *qr.lines){os << "\t(行号 " << num + 1 << ")"<< *(qr.file->cbegin() + num) << endl;}return os;
}int main(){ifstream infile("/home/ys/cpp/thread/oop/TextQuery/search_text");TextQuery tq(infile);//Query q = Query("fiery") & Query("bird") | Query("wind");//OK//Query q = Query("fiery") | Query("bird");//OK//Query q("Daddy");//OKQuery q = ~Query("Alice");//OKprint(std::cout, q.eval(tq)) << std::endl;
}

编译方法：

g++ -g Query.cpp TextQuery.cpp main.cpp -std=c++11

用于查询的文本文件

Alice Emma has long flowing red hair.
Her Daddy says when the wind blows
through her hair, it looks almost alive,
like a fiery bird in flight.
A beautiful fiery bird, he tells her,
magical but untamed.
" Daddy , shush, there is no such thing,"
she tells him, at the same time wanting
him to tell her more.
Shyly, she asks, "I mean, Daddy , is there?"

Query q = Query("fiery") & Query("bird") | Query("wind");的执行结果：

((fiery & bird) | wind) 出现了：2次(行号 2)Her Daddy says when the wind blows(行号 4)like a fiery bird in flight.

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