c/c++ 繼承與多型 文字查詢的小例子(非智慧指標版本)
阿新 • • 發佈:2019-01-10
問題:在上一篇繼承與多型 文字查詢的小例子(智慧指標版本)在Query類裡使用的是智慧指標,只把智慧指標換成普通的指標,並不新增拷貝構造方法,會發生什麼呢?
執行時,程式碼崩掉。
分析下面一行程式碼:
Query qb = ~Query("Alice");
1,首先呼叫Query(string)的建構函式,把Query的成員q指向了new WordQuery(s)
Query::Query(const std::string& s) : q(new WordQuery(s)){ std::cout << "Query pub" << std::endl; }
2,呼叫WordQuery的建構函式
3,呼叫過載的operator~方法,引數是在1處的Query的無名的臨時物件
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,呼叫NotQuery的構造方法,引數是在1處的Query的無名的臨時物件。query(q)是呼叫了Query的合成的拷貝構造方法,所以NotQuery的私有成員query和1處的Query的無名的臨時物件 的成員q都指向了在2處構建的WordQuery的物件。
NotQuery(const Query& q)
:query(q){
std::cout << "NotQuery" << std::endl;
}
5,return Query(tmp);呼叫了Query的建構函式,又做出了一個Query物件。這個Query的q成員指向了在4處做成的NotQuery物件,這個NotQuery物件的query成員的q成員指向了在2處做成的WordQuery物件。
Query(Query_base* qb)
:q(qb){}
6,把在5處做成的Query物件,給qb【Query qb = ~Query("Alice");】,這個時點,在1處的Query的無名的臨時物件 ,已經沒有用了,就會釋放它,就會呼叫Query的解構函式,解構函式會delete p;這個p指向的是2處的WordQuery。
接下來執行:
print(std::cout, qb.eval(tq)) << std::endl;
這時qb的q指向的是4處NotQuery,4處的NotQuery的query的q,也是指向2處的WordQuery。這時qb去呼叫eval方法時,用qb裡的q指向的NotQuery呼叫eval,然後用NotQuery裡query的q去呼叫WorQuery的eval方法,可是NotQuery裡query的q指向的2處的WordQuery已經被釋放,程式就蹦了(segment core error)。
怎麼解決? 自定義拷貝建構函式。
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&);//需要訪問私有的建構函式
friend Query operator|(const Query&, const Query&);//需要訪問私有的建構函式
friend Query operator&(const Query&, const Query&);//需要訪問私有的建構函式
public:
Query(const std::string&);//構建一個新的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;
}
// 介面函式:呼叫對應的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的私有建構函式
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){//呼叫Query的拷貝建構函式
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通過它的Query_base指標對rep()進行虛呼叫
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{
//通過Query運算物件對eval進行虛呼叫
auto result = query.eval(text);
//開始時結果set為空
auto ret_lines = std::make_shared<std::set<line_no>>();
auto beg = result.begin();
auto end = result.end();
//對於輸入檔案的每一行,如果該行不在result當中,則將其新增到ret_lines
auto sz = result.get_file()->size();
for(size_t n = 0; n != sz; ++n){
//如果還沒有處理完result的所以行
//檢查當前行是否存在
if(beg == end || *beg != n){
ret_lines->insert(n);
}
else if(beg != end){
++beg;//繼續獲取reslut的下一行
}
}
return QueryResult(rep(), ret_lines, result.get_file());
}
QueryResult AndQuery::eval(const TextQuery& text)const{
//通過Query成員lhs,rhs進行虛呼叫
//呼叫eval返回每個物件的QueryResult
auto right = rhs.eval(text);
auto left = lhs.eval(text);
//儲存left和right交集的set
auto ret_lines =
std::make_shared<std::set<line_no>>();
//將兩個範圍的交集寫入一個目的迭代其中。
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{
//通過Query成員lhs,rhs進行虛呼叫
//呼叫eval返回每個物件的QueryResult
auto right = rhs.eval(text);
auto left = lhs.eval(text);
//將左側運算物件的行號拷貝到結果set中
auto ret_lines =
std::make_shared<std::set<line_no>>(left.begin(), left.end());
//插入右側運算物件所得的行號
ret_lines->insert(right.begin(), right.end());
//返回一個新的QueryResult,它表示lhs和rhs的並集
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;//查詢的單詞
std::shared_ptr<std::set<line_no>> lines;//出現的行號
std::shared_ptr<std::vector<std::string>> file;
};
//QueryResult類的友元宣告
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)){//讀檔案的每一行
file->push_back(text);
int n = file->size() - 1;//當前行號
istringstream line(text);//將行文字分解為單詞
string word;
while(line >> word){
//非常重要,必須用引用,要不然就會拷貝一個新的set給lines,不是原來的
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{
//如果沒有找到sought,返回指向此set的一個智慧指標
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);//沒有找到
}
else{
return QueryResult(sought, ret->second, file);
}
}
main.cpp
#include "Query.h"
//QueryResult的友元函式
ostream& print(ostream& os, const QueryResult& qr){
os << qr.sought << " 出現了:" << qr.lines->size() << "次" << endl;
for(auto num : *qr.lines){
os << "\t(行號 " << 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");//OK
Query q = ~Query("Alice");//OK
print(std::cout, q.eval(tq)) << std::endl;
}
編譯方法:
g++ -g Query.cpp TextQuery.cpp main.cpp -std=c++11
用於查詢的文字檔案
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");的執行結果:
((fiery & bird) | wind) 出現了:2次
(行號 2)Her Daddy says when the wind blows
(行號 4)like a fiery bird in flight.