使用map实现单词转换的程序

使用map实现单词转换的程序

从map中查找单词时必须使用find函数，不能使用下表，因为在map中使用下标访问不存在的元素将导致在map容器中添加一个新的元素，新元素的key即要查找的内容。

/*****************************************************************************
* Open file
*****************************************************************************/
ifstream& open_file(ifstream &in, const string &file)
{
	in.close();  // close in case it was already open
	in.clear();  // clear any existing errors

	// if the open fails, the stream will be in an invalid state
	in.open(file.c_str()); // open the file we were given

	return in; // condition state is good if open succeeded
}


/*****************************************************************************
* Word Transform
*****************************************************************************/
void WordTransform(const string rule, const string infile)
{
	if (rule.empty() || infile.empty())
	{
		return;
	}

	map<string ,string> trans_map;
	string key, value;

	// Open transformation file and check that open succeeded
	ifstream map_file;
	if (!open_file(map_file, rule))
	{
		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));
	}

	// Open the input file and check that the open succeeded
	ifstream input;
	if (!open_file(input, infile))
	{
		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 at a time
		string word;
		bool bFirstWordFlg = true;	// Controls whether 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 != trans_map.end())
			{
				// Replace it by the transformaion value in the map
				word = map_it->second;
			}

			if (bFirstWordFlg)
			{
				bFirstWordFlg = false;
			}
			else
			{
				cout << " ";	// Print space between words
			}

			cout << word;
		}
		cout << endl;	// Done with this line of input
	}
}