C++Primer第五版习题答案第十七章标准库特殊设施（Specialized Library Facilities）_重写12.3节中的textquery程序,使用tuple代替queryresult-优快云博客

练习17.1

定义一个保存三个 int 值的 tuple，并将其成员分别初始化为10、20和30。

#include <iostream>
#include <tuple>
#include <vector>

int main()
{
   
   
	std::tuple<int, int, int> threeI(10, 20, 30);
	std::tuple<std::string, std::vector<std::string>, std::pair<std::string, int>> someVal("constants", {
   
   "a", "bb"}, {
   
   "ccc", 3});

	return 0;
}

练习17.2

定义一个 tuple，保存一个 string、一个vector 和一个 pair<string, int>。

参见17.1。

练习17.3

重写12.3节中的 TextQuery 程序，使用 tuple 代替 QueryResult 类。你认为哪种设计更好？为什么？

第一种设计更好，第二种设计更容易实现，但不容易重构。

#ifndef TEXTQUERY_H_
#define TEXTQUERY_H_

#include <string>
#include <vector>
#include <map>
#include <fstream>
#include <sstream>
#include <set>
#include <memory>
#include <iostream>
#include <algorithm>
#include <iterator>
#include "StrBlob.h"
#include "DebugDelete.h"
#include <tuple>

class QueryResult;

class TextQuery
{
   
   
public:
	using line_no = std::vector<std::string>::size_type;
	TextQuery(std::ifstream&);
	std::tuple<std::string, std::shared_ptr<std::set<TextQuery::line_no>>, StrBlob> query(const std::string&) const;
private:
	StrBlob file;
	std::map<std::string, std::shared_ptr<std::set<line_no>>> word_map;
};

class QueryResult
{
   
   
	friend std::ostream& print(std::ostream&, const QueryResult&);
public:
	QueryResult(std::string s, std::shared_ptr<std::set<TextQuery::line_no>> p, StrBlob f) : sought(s), lines(p), file(f) {
   
    }
	std::set<StrBlob::size_type>::iterator begin() const {
   
    return lines->begin(); }
	std::set<StrBlob::size_type>::iterator end() const {
   
    return lines->end(); }
	// std::shared_ptr<StrBlob> get_file() const { return std::make_shared<StrBlob>(file); }
	const StrBlob& get_file() const {
   
    return file; }
private:
	std::string sought;
	std::shared_ptr<std::set<TextQuery::line_no>> lines;
	StrBlob file;
};

TextQuery::TextQuery(std::ifstream &ifs)
{
   
   
	std::string text_line;

	while(std::getline(ifs, text_line))
	{
   
   
		file.push_back(text_line);
		int line_number = file.size() - 1;
		std::istringstream line(text_line);
		std::string text_word;
		while(line >> text_word)
		{
   
   
			std::string word;
			std::copy_if(text_word.begin(), text_word.end(), std::back_inserter(word), isalpha);
			// std::cout << word << std::endl;
			auto &wm_lines = word_map[word];
			if(!wm_lines)
				wm_lines.reset(new std::set<line_no>, DebugDelete());
			wm_lines->insert(line_number);
		}
	}
}

std::tuple<std::string, std::shared_ptr<std::set<TextQuery::line_no>>, StrBlob> TextQuery::query(const std::string &sought) const
{
   
   
	static std::shared_ptr<std::set<TextQuery::line_no>> nodata(new std::set<TextQuery::line_no>);
	auto loc = word_map.find(sought);
	if(loc == word_map.end())
		return std::tuple<std::string, std::shared_ptr<std::set<TextQuery::line_no>>, StrBlob>(sought, nodata, file);
	else
		return std::tuple<std::string, std::shared_ptr<std::set<TextQuery::line_no>>, StrBlob>(sought, loc->second, file);
}

std::ostream &print(std::ostream &os, const QueryResult &qr)
{
   
   
	os << qr.sought << " occurs " << qr.lines->size() << " " /*<< make_plural(qr.lines->size(), "time", "s")*/ << std::endl;
	for(auto num : *qr.lines)
	{
   
   
		ConstStrBlobPtr p(qr.file, num);
		os << "\t(line " << num + 1 << ") " << p.deref() << std::endl;
	}
		
	return os;
}

#endif

练习17.4

编写并测试你自己版本的 findBook 函数。

#include <iostream>
#include <string>
#include "Sales_data.h"
#include <unordered_set>
#include <algorithm>
#include <tuple>

namespace std
{
   
   
	template <>
	struct hash<Sales_data>
	{
   
   
		typedef size_t result_type;
		typedef Sales_data argument_type;
		size_t operator()(const Sales_data &s) const;
	};
	size_t hash<Sales_data>::operator()(const Sales_data &s) const
	{
   
   
		return hash<std::string>()(s.bookNo) ^ hash<unsigned>()(s.units_sold) ^ hash<double>()(s.revenue);
	}
}

bool compareIsbn(const Sales_data &lhs, const Sales_data &rhs)
{
   
   
	return lhs.isbn() < rhs.isbn();
}

typedef std::tuple<std::vector<Sales_data>::size_type, std::vector<Sales_data>::const_iterator, std::vector<Sales_data>::const_iterator> matches;

std::vector<matches> findBook(const std::vector<std::vector<Sales_data>> &files, const std::string &book)
{
   
   
	std::vector<matches> ret;
	for(auto it = files.cbegin(); it != files.cend(); ++it)
	{
   
   
		auto found = std::equal_range(it->cbegin(), it->cend(), Sales_data(book), compareIsbn);
		if(found.first != found.second)
			ret.push_back(std::make_tuple(it - files.cbegin(), found.first, found.second));
	}
	return ret;
}

void reportResults(std::istream &in, std::ostream &os, const std::vector<std::vector<Sales_data>> &files)
{
   
   
	std::string s;
	while(in >> s)
	{
   
   
		auto trans = findBook(files, s);
		if(trans.empty())
		{
   
   
			std::cout << s << " not found in any stores" << std::endl;
			continue;
		}
		for(const auto &store : trans)
			os << "store " << std::get<0>(store) << " sales: " << std::accumulate(std::get<1>(store), std::get<2>(store), Sales_data(s)) << std::endl;
	}
}

int main()
{
   
   
    Sales_data sales_data1("001-01", 1, 100);
    Sales_data sales_data2("001-01", 2, 100);
    Sales_data sales_data3("001-02", 2, 80);

    std::vector<Sales_data> vs1 = {
   
   sales_data1, sales_data3};
    std::vector<Sales_data> vs2 = {
   
   sales_data2};
    std::vector<std::vector<Sales_data>> vvs = {
   
   vs1, vs2};

    reportResults(std::cin, std::cout, vvs);

 //    std::cout << std::hex << std::hash<std::string>()("001-01") << std::endl;
 //    std::cout << std::hex << std::hash<unsigned>()(1) << std::endl;
 //    std::cout << std::hex << std::hash<double>()(100) << std::endl;

 //    std::unordered_multiset<Sales_data> SDset;
 //    SDset.emplace(sales_data1);
 //    SDset.emplace("001-03", 1, 200);
 //    SDset.emplace(sales_data3);

	// for(const auto &item : SDset)
	// 	std::cout << "the hash code of " << item.isbn() <<":\n0x" << std::hex << std::hash<Sales_data>()(item) << "\n";

    return 0;
}

练习17.5

重写 findBook，令其返回一个 pair，包含一个索引和一个迭代器pair。

#include <iostream>
#include <string>
#include "Sales_data.h"
#include <unordered_set>
#include <algorithm>
#include <utility>

namespace std
{
   
   
	template <>
	struct hash<Sales_data>
	{
   
   
		typedef size_t result_type;
		typedef Sales_data argument_type;
		size_t operator()(const Sales_data &s) const;
	};
	size_t hash<Sales_data>::operator()(const Sales_data &s) const
	{
   
   
		return hash<std::string>()(s.bookNo) ^ hash<unsigned>()(s.units_sold) ^ hash<double>