Chapter 11.Associative Containers

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本文探讨了关联容器与顺序容器在数据存储和检索方式上的根本不同，通过具体实例介绍了如何使用 C++ 中的 map 容器来实现基于键值的数据映射与转换。

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关联容器和顺序容器有着根本的不同。Associative and sequential containers differ from one another in a fundamental way:Elements in an associative container are stored andretrieved by a key. In contrast,elements in a sequential container are stored and accessed sequentially by their position in the container.

retrieve data 检索数据 retrieve 取回检索挽回

练习11.33：

#include <iostream>
#include <map>
#include <string>
#include <fstream>//file stream
#include <sstream>

using std::string;
using std::ifstream;

std::map<string, string> buildMap(ifstream& map_file)
{
	std::map<string, string> trans_map;
	for (string key, value; map_file >> key && getline(map_file, value);)
		if (value.size() > 1)
			trans_map[key] =value.substr(1).substr(0, value.find_last_not_of(' '));
	return trans_map;
}

const string& transform(const string& s, const std::map<string, string>& m)
{
	auto map_it = m.find(s);
	return map_it == m.cend() ? s : map_it->second;
}

void word_transform(ifstream& map, ifstream& input)//ifstream(input file stream)//ofstream(output file stream)
{
	auto trans_map = buildMap(map);
	for (string text; getline(input, text);) 
	{
		std::istringstream iss(text);
		for (string word; iss >> word;)
			std::cout << transform(word, trans_map) << " ";
		std::cout << std::endl;
	}
}

int main()
{
	ifstream ifs_map("C:/Users/Administrator/Desktop/given_to_transform.txt"),
		ifs_content("C:/Users/Administrator/Desktop/word_transformation_bad.txt");
	if (ifs_map && ifs_content)
		word_transform(ifs_map, ifs_content);
	else
		std::cerr << "can't find the documents." << std::endl;
	system("pause");
}