C++ Primer 关联容器 单词转换程序

/*
  此代码来自 C++ Primer，手敲一遍是因为：
  1. 今天刚好开始学数据结构，好的算法的要满足 健壮性(数据非法时，也能适当作出反应或进行处理) 和 可读性 (便于理解和修改，按照老师的说法，主要体现在注释上)，上完课后看C++ Primer，发现下面这段代码，在这两方面就做得比较好，值得学习
  
  2. 因为STL学得还是不太扎实，只是在做题中偶尔用到，但没有系统地学...所以才会重新看书，而只看不敲的话，仍然得不到巩固，记忆也不会深刻
  
  同时，main函数的这种写法，以前虽然看到过，但没有仔细研究，今天仔细查了相关资料了解了一下，发现这个博客讲得很详细
  http://www.cnblogs.com/avril/archive/2010/03/22/1691477.html
  
*/

//#include <bits/stdc++.h>
#include <iostream>
#include <map>
using namespace std;
/*
 * A program to transform words.
 * Takes two arguments: The first is name of the word transformation file
 						The second is name of input to transformation
 *
 */
 int main(int argc, char** argv)
 {
 	// map to hold the word transformation pairs:
 	// key is the word to look for in the input; value is word to use in the output
 	map<string, string> trans_map;
 	string key, value;
 	
 	if (argc != 3)
 	throw runtime_error ("wrong number of arguments");
 	
 	// open transformatino file and check that open succeeded
 	ifstream map_file;
 	if (!open_file(map_file, argv[1]))
 	throw runtime_error("no transformation file");
 	
 	// read the transformation map and build the map
 	while (map_file >> key >> value)
 	trans_map.insert(make_pair(key, value));
 	
 	// ok, now we're ready to do the transformations
 	// opne the input file and check that the open succeeded
 	ifstream input;
 	if (!open_file(input, argv[2]))
 	throw runtime_error("no input file");
 	
 	string line; // hold each line from the input
 	// read the text to transform it a line at a time
 	while (getline(input, line))
 	{
 		istringstream stream(line); // read the line a word a time
 		string word;
 		bool firstword = true; // controls wheter a space is printed
 		while (stream >> word)
 		{
 			// ok: the actual mapwork, this part is the heart of the program
 			map<string, string>::const_iterator map_it = trans_map.find(word);
 			// if this word is in the transformation map
 			if (map_it != tran_map.end())
 			// replace it by the transformation value int the map
 			word = map_it->second;
 			
 			if (firstword) firstword = false;
 			else
 			cout << " "; // print space between words
 			cout << word;
		 }
		 cout << endl;
	 }
	 return 0;
 }