最近在看C++ Primer复习C++的语法，看到书中15.9章中的文本查询示例时，觉得设计得非常不错，于是便动手照着实现了一个，修改了很久终于运行成功了，从中也学习到了很多的语法。下面把实现与总结分享给大家：
首先是在10.6.2节中实现的TextQuery类：
TextQuery.h
#ifndef __TestC____TextQuery__
#define __TestC____TextQuery__
#include <iostream>
#include <vector>
#include <set>
#include <map>
using namespace std;
class TextQuery {
public:
typedef vector<string>::size_type line_no;
TextQuery(string[], vector<string>::size_type);
set<line_no> run_query(const string&) const;
line_no size() const;
private:
vector<string> lines_of_text;
};
#endif /* defined(__TestC____TextQuery__) */
TextQuery.cpp
#include "TextQuery.h"
TextQuery::TextQuery(string strArray[], vector<string>::size_type count) {
lines_of_text.assign(strArray, strArray+count);
}
set<TextQuery::line_no> TextQuery::run_query(const string&word) const {
set<line_no> ret_lines;
for (int i=0;i<lines_of_text.size();i++) {
string line = lines_of_text[i];
if (line.find(word) != string::npos) {
ret_lines.insert(i);
}
}
return ret_lines;
}
TextQuery::line_no TextQuery::size() const {
return lines_of_text.size();
}
接下来是查询类的句柄类Query：
Query.h
#ifndef __TestC____Query__
#define __TestC____Query__
#include <iostream>
#include "TextQuery.h"
class Query_base;
class Query {
friend Query operator~(const Query &);
friend Query operator|(const Query &, const Query &);
friend Query operator&(const Query &, const Query &);
public:
Query(const string &);
Query(const Query &);
virtual ~Query();
Query& operator=(const Query&);
set<TextQuery::line_no> eval(const TextQuery&) const;
ostream & display(ostream &) const;
private:
Query(Query_base *);
Query_base *q;
size_t *use;
void decr_use();
};
inline ostream & operator<<(ostream &os, const Query &q) {
return q.display(os);
}
#endif /* defined(__TestC____Query__) */
Query.cpp
#include "Query.h"
#include "Query_base.h"
Query::Query(const Query &c) : q(c.q), use(c.use) {
++*use;
}
Query::Query(const string &s) : q(new WordQuery(s)), use(new size_t(1)) {
}
Query::Query(Query_base *query) : q(query), use(new size_t(1)) {
}
Query::~Query() {
decr_use();
}
void Query::decr_use() {
if (--*use == 0) {
delete q;
delete use;
}
}
set<TextQuery::line_no> Query::eval(const TextQuery &t) const{
return q->eval(t);
}
ostream& Query::display(ostream &os) const {
return q->display(os);
}
接下来是最核心的各个查询类Query_base、WordQuery、NotQuery、AndQuery、OrQuery：
Query_base.h
#ifndef __TestC____Query_base__
#define __TestC____Query_base__
#include <iostream>
#include "TextQuery.h"
#include "Query.h"
class Query_base {
friend class Query;
protected:
typedef TextQuery::line_no line_no;
virtual ~Query_base() {}
private:
virtual set<line_no> eval(const TextQuery&) const = 0;
virtual ostream & display(ostream & = cout) const = 0;
};
class WordQuery : Query_base {
friend class Query;
WordQuery(const string &);
set<line_no> eval(const TextQuery&) const;
ostream & display(ostream & = cout) const;
string query_word;
};
class NotQuery : public Query_base {
friend Query operator~(const Query &);
NotQuery(Query);
set<line_no> eval(const TextQuery&) const;
ostream & display(ostream & = cout) const;
const Query query;
};
class BinaryQuery : public Query_base {
protected:
BinaryQuery(Query left, Query right, string op);
ostream & display(ostream & = cout) const;
const Query lhs, rhs;
const string oper;
};
class AndQuery : BinaryQuery {
friend Query operator&(const Query&, const Query&);
AndQuery(Query left, Query right);
set<line_no> eval(const TextQuery&) const;
};
class OrQuery : BinaryQuery {
friend Query operator|(const Query&, const Query&);
OrQuery(Query left, Query right);
set<line_no> eval(const TextQuery&) const;
};
#endif /* defined(__TestC____Query_base__) */
Query_base.cpp
#include "Query_base.h"
/**
* WordQuery
*/
WordQuery::WordQuery(const string &s) : query_word(s) {
}
set<WordQuery::line_no> WordQuery::eval(const TextQuery &t) const {
return t.run_query(query_word);
}
ostream & WordQuery::display(ostream &os) const {
return os << query_word;
}
/**
* NotQuery
*/
NotQuery::NotQuery(Query q) : query(q) {
}
set<NotQuery::line_no> NotQuery::eval(const TextQuery &file) const {
set<line_no> has_val = query.eval(file);
set<line_no> ret_lines;
for (TextQuery::line_no n = 0; n != file.size(); ++n) {
if (has_val.find(n) == has_val.end()) {
ret_lines.insert(n);
}
}
return ret_lines;
}
ostream & NotQuery::display(ostream &os) const {
return os << "~(" << query << ")";
}
/**
* BinaryQuery
*/
BinaryQuery::BinaryQuery(Query left, Query right, string op) : lhs(left), rhs(right), oper(op) {
}
ostream & BinaryQuery::display(ostream &os) const {
return os << "(" << lhs << " " << oper << " "
<< rhs << ")";
}
/**
* AndQuery
*/
AndQuery::AndQuery(Query left, Query right) : BinaryQuery(left, right, "&") {
}
set<AndQuery::line_no> AndQuery::eval(const TextQuery&file) const {
set<line_no> left = lhs.eval(file), right = rhs.eval(file);
set<line_no> ret_lines;
set_intersection(left.begin(), left.end(),
right.begin(), right.end(),
inserter(ret_lines, ret_lines.begin()));
return ret_lines;
}
/**
* OrQuery
*/
OrQuery::OrQuery(Query left, Query right) : BinaryQuery(left, right, "|") {
}
set<OrQuery::line_no> OrQuery::eval(const TextQuery&file) const {
set<line_no> right = rhs.eval(file), ret_lines = lhs.eval(file);
ret_lines.insert(right.begin(), right.end());
return ret_lines;
}
下面是以上代码的用法示例：
main.cpp
#include "Query.h"
#include "Query_base.h"
using namespace std;
inline Query operator~(const Query &oper) {
return new NotQuery(oper);
}
inline Query operator|(const Query &left, const Query &right) {
return new OrQuery(left, right);
}
inline Query operator&(const Query &left, const Query &right) {
return new AndQuery(left, right);
}
int main(int argc, const char * argv[])
{
string article[] = {
"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"));
set<vector<string>::size_type> result = q.eval(TextQuery(article, sizeof(article)/sizeof(article[0])));
for (set<vector<string>::size_type>::iterator iter = result.begin(); iter != result.end(); iter++) {
cout << *iter+1 << endl;
}
return 0;
}
以上代码中需要注意的语法点有：
1. Query的几个重载操作符如果作为inline函数的话，必须放在定义的头文件或者用到重载操作符的实现文件中，在本例中如果放在Query.h文件中，由于需要引入Query_base.h文件，会导致头文件循环引用的问题，因此放在了main函数中。<<操作符由于没有使用其他类，所以可以放在Query_base.h文件中。
2. 由于NotQuery、OrQuery、AndQuery几个类的构造函数都是私有的，因此必须将使用到这几个类的函数声明为友元函数，在本例中为&、|、~几个操作符函数。
如果大家觉得对自己有帮助的话，还希望能帮顶一下，谢谢：）
转载请注明出处，谢谢！