为了更好的理解继承和多态，做一个文本查询的小例子。
接口类：Query有2个方法。
- eval：查询，返回查询结果类QueryResult
- rep：得到要查询的文本
客户端程序的使用方法：
//查询包含Daddy的文本所在的行
Query q("Daddy");
//查询不包含Alice的文本所在的行
Query q = ~Query("Alice");
//查询，有fiery或者bird的行
Query q = Query("fiery") | Query("bird");
//查询，既有fiery又bird的行，或者有wind的行
Query q = Query("fiery") & Query("bird") | Query("wind");
接口类：Query，有一个私有的父类Query_base的智能指针。
-
父类Query_base有子类WordQuery，NotQuery，BinaryQuery（AndQuery，OrQuery）。
-
子类负责把单个的查询结果，进行加工。比如做And处理，或者Or处理。
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;
};
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
// 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;
}
std::shared_ptr<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;
}
std::string query_word;
};
class NotQuery : public Query_base{
friend Query operator~(const Query&);
NotQuery(const Query& q)
:query(q){
std::cout << "NotQuery" << std::endl;
}
std::string rep() const {
return "~(" + query.rep() + ")";
}
QueryResult eval(const TextQuery&)const;
Query query;
};
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);
}
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;
};
inline Query operator&(const Query& lhs, const Query& rhs){
return std::shared_ptr<Query_base>(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;
}
QueryResult eval(const TextQuery&) const;
};
inline Query operator|(const Query& lhs, const Query& rhs){
return std::shared_ptr<Query_base>(new OrQuery(lhs, rhs));
}
#endif
Query.cpp
#include "Query.h"
#include <algorithm>
/*
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_lines
auto 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QueryResult
auto right = rhs.eval(text);
auto left = lhs.eval(text);
//保存left和right交集的set
auto 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QueryResult
auto 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 << " (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");//OK
Query q = ~Query("Alice");//OK
print(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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