C++ Primer 中的textquery例子
要求
- 从文本读取数据并构建查询表
- 返回查询结果
- 分析查询操作
- 支持操作与或非运算
interface
- TextQuery
- QueryResult
- Query: 保存需要的执行的操作
- 支持从字符串建立单词查询
- 支持 & | ~ 操作符
实现
TextQuery 和 QueryResult
查询结果需要输出行号和该行内容. 可以建立单词与行号集合的查询表.
std::map> searchTable;
使用vector保存每行内容.
因为这些内容在查询结果中也要使用, 可以使用智能指针方便内容共享
结果中需要有行号集合的指针. 为了输出需要每行内容的指针
// 声明文件
class QueryResult;
class TextQuery{
using line_no = std::vector::size_type;
public:
TextQuery() = default;
TextQuery(std::ifstream&);
QueryResult query(const std::string&) const;
private:
std::shared_ptr> textContent;
std::map>> searchTable;
};
class QueryResult{
public:
using line_no = TextQuery::line_no;
using iterator = std::set::iterator;
QueryResult(const std::string& _query,
std::shared_ptr> _content,
std::shared_ptr> _result = std::make_shared>())
: query(_query)
, content(_content)
, result(_result)
{}
std::set::iterator begin() { return result->begin(); }
std::set::iterator end() { return result->end(); }
std::shared_ptr> get_content(){return content;}
friend std::ostream& operator<<(std::ostream&, const QueryResult&);
private:
const std::string query;
std::shared_ptr> content;
std::shared_ptr> result;
};
函数实现
TextQuery::TextQuery(istream& in)
{
string line;
while (getline(in, line))
{
textContent->emplace_back(line);
istringstream ss(line);
string word;
line_no n = textContent->size() - 1;
while (ss >> word)
{
auto p = searchTable[word];
if (!p) p.reset(new set);
p->insert(n);
}
}
}
QueryResult TextQuery::query(const string& sought) const
{
auto res = searchTable.find(sought);
if (res == searchTable.end()) return QueryResult(sought, textContent);
return QueryResult(sought, textContent, res->second);
}
ostream& operator<<(ostream& os, const QueryResult& res)
{
os << res.query << " occurs " << res.result->size() << (res.result->size() > 1 ? "times" : "time") << endl;
for (auto l : *res.result) os << "\t(line " << l + 1 << (*res.content)[l] << ")" << endl;
return os;
}
Query
因为要支持与, 或, 非(&, |, ~)运算. 每种查询执行的操作不同, 定义一个抽象基类. 有两个纯虚函数 rep() 返回该查询操作的字符串描述. eval() 执行查询
derived.png
QueryBase
class QueryBase{
friend class Query;
protected:
virtual ~QueryBase() = default;
private:
virtual QueryResult eval(const TextQuery&) const = 0;
virtual std::string rep() const = 0;
};
// Query
class Query{
friend Query operator&(const Query&, const Query&);
friend Query operator|(const Query&, const Query&);
friend Query operator~(const Query&);
public:
Query(const std::string&);
QueryResult eval(const TextQuery& t){return q->eval(t);}
std::string rep(){return q->rep();}
private:
std::shared_ptr q;
Query(std::shared_ptr _q):q(_q){}
};
WordQuery
class WordQuery:public QueryBase{
friend class Query;
WordQuery(const std::string& s):word(s){}
QueryResult eval(const TextQuery& t) { return t.query(word);}
std::string rep() {return word;}
std::string word;
};
Query::Query(const string& w):q(new WordQuery(w)){}
NotQuery 和 ~操作
class NotQuery : public QueryBase {
friend Query operator~(const Query&);
NotQuery(const Query& q) : query(q) {}
QueryResult eval(const TextQuery&) const;
std::string rep() const
{
return "~(" + query.rep() + ")";
}
Query query;
};
inline Query operator&(const Query&lhs, const Query& rhs)
{
return shared_ptr(new AndQuery(lhs, rhs));
}
BinartQuery
class BinaryQuery : public QueryBase {
protected:
BinaryQuery(const Query& _lhs, const Query& _rhs, std::string _op) : lhs(_lhs), rhs(_rhs), op(_op) {}
std::string rep() const override
{
return "(" + lhs.rep() + " " + op + " " + rhs.rep() + ")";
}
Query lhs, rhs;
std::string op;
};
AndQuery 和 OrQuery
class AndQuery : public BinaryQuery {
friend Query operator&(const Query& lhs, const Query& rhs);
AndQuery(const Query& lhs, const Query& rhs) : BinaryQuery(lhs, rhs, "&") {}
QueryResult eval(const TextQuery&) const;
};
class OrQuery : public BinaryQuery {
friend Query operator|(const Query& lhs, const Query& rhs);
OrQuery(const Query& lhs, const Query& rhs) : BinaryQuery(lhs, rhs, "|") {}
QueryResult eval(const TextQuery&) const;
};
inline Query operator&(const Query&lhs, const Query& rhs)
{
return shared_ptr(new AndQuery(lhs, rhs));
}
inline Query operator|(const Query&lhs, const Query& rhs)
{
return shared_ptr(new OrQuery(lhs, rhs));
}
核心 eval 实现
QueryResult OrQuery::eval(const TextQuery& t) const
{
auto left = lhs.eval(t);
auto right = rhs.eval(t);
auto res = make_shared>(left.begin(), left.end());
res->insert(right.begin(), right.end());
return QueryResult(rep(), left.get_content(), res);
}
QueryResult AndQuery::eval(const TextQuery& t) const
{
auto left = lhs.eval(t);
auto right = rhs.eval(t);
auto res = make_shared>();
set_intersection(left.begin(), left.end(), right.begin(), right.end(), inserter(*res, res->begin()));
return QueryResult(rep(), left.get_content(), res);
}
QueryResult OrQuery::eval(const TextQuery& t) const
{
auto left = lhs.eval(t);
auto right = rhs.eval(t);
auto res = make_shared>(left.begin(), left.end());
res->insert(right.begin(), right.end());
return QueryResult(rep(), left.get_content(), res);
}
QueryResult AndQuery::eval(const TextQuery& t) const
{
auto left = lhs.eval(t);
auto right = rhs.eval(t);
auto res = make_shared>();
set_intersection(left.begin(), left.end(), right.begin(), right.end(), inserter(*res, res->begin()));
return QueryResult(rep(), left.get_content(), res);
}
命令分析
为了简便有一些限制
- 不能有空格
- 没有转义字符. 无法搜索包含 &|~的单词
- 表达式错误, 程序会崩溃.
Query parseQuery(const string& com)
{
static map opPriority{{')', 0}, {'|', 1}, {'&', 2}, {'~', 3}, {'(', 4}};
stack stOp;
stack stQuery;
string::const_iterator cur = com.begin();
string::const_iterator end = com.end();
while (cur != end)
{
if (opPriority.count(*cur))
{
while (!stOp.empty() && opPriority[*cur] <= opPriority[stOp.top()])
{
char op = stOp.top();
stOp.pop();
switch (op)
{
case '~': {
Query q = stQuery.top();
stQuery.pop();
stQuery.push(~q);
break;
}
case '&': {
Query r = stQuery.top();
stQuery.pop();
Query l = stQuery.top();
stQuery.pop();
stQuery.push(l & r);
break;
}
case '|': {
Query r = stQuery.top();
stQuery.pop();
Query l = stQuery.top();
stQuery.pop();
stQuery.push(l | r);
}
default: break;
}
}
if (*cur == '(')
stOp.push(')');
else if (*cur != ')')
stOp.push(*cur);
++cur;
}
else
{
string::const_iterator temp = cur;
while (cur != end && !opPriority.count(*cur)) ++cur;
stQuery.emplace(string(temp, cur));
}
}
return stQuery.top();
}