C++ Primer 5th笔记（chap 11）关联容器---举例

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1. code

#ifndef WORDTRANSFORM_H 
#define WORDTRANSFORM_H
  
#include <map>
#include <vector>
#include <iostream>
#include <fstream>
#include <string>
#include <stdexcept>
#include <sstream>

using std::map; using std::string; using std::vector;
using std::ifstream; using std::cout; using std::endl;
using std::getline;
using std::runtime_error; using std::istringstream;


class wordTransform {
public:
	wordTransform(){}

	virtual ~wordTransform() {}
	 

	map<string, string> buildMap(ifstream& map_file)
	{
		map<string, string> trans_map;   // holds the transformations
		string key;    // a word to transform
		string value;  // phrase to use instead
		// read the first word into key and the rest of the line into value
		while (map_file >> key && getline(map_file, value))
			if (value.size() > 1) // check that there is a transformation
				trans_map[key] = value.substr(1); // skip leading space 
			else
				throw runtime_error("no rule for " + key);
		return trans_map;
	}

	const string&
		transform(const string& s, const map<string, string>& m)
	{
		// the actual map work; this part is the heart of the program
		auto map_it = m.find(s);
		// if this word is in the transformation map
		if (map_it != m.cend())
			return map_it->second; // use the replacement word
		else
			return s;              // otherwise return the original unchanged
	}

	// first argument is the transformations file; 
	// second is file to transform
	void word_transform(ifstream& map_file, ifstream& input)
	{
		auto trans_map = buildMap(map_file); // store the transformations

		// for debugging purposes print the map after its built
		cout << "Here is our transformation map: \n\n";
		for (auto entry : trans_map)
			cout << "key: " << entry.first
			<< "\tvalue: " << entry.second << endl;
		cout << "\n\n";

		// do the transformation of the given text 
		string text;                    // hold each line from the input
		while (getline(input, text)) {  // read a line of input
			istringstream stream(text); // read each word 
			string word;
			bool firstword = true;      // controls whether a space is printed 
			while (stream >> word) {
				if (firstword)
					firstword = false;
				else
					cout << " ";  // print a space between words
				// transform returns its first argument or its transformation 
				cout << transform(word, trans_map); // print the output 
			}
			cout << endl;        // done with this line of input
		}
	}

	void test() { 
		ifstream map_file("e:/temp/rules"); // open transformation file 
		if (!map_file)              // check that open succeeded
			throw runtime_error("no transformation file");

		ifstream input("e:/temp/text");    // open file of text to transform
		if (!input)                 // check that open succeeded
			throw runtime_error("no input file");

		word_transform(map_file, input);
	}
	 
};
 
#endif

2. 原始文件

rules:

brb be right back
k okay?
y why
r are
u you
pic picture
thk thanks!
l8r later

3. 输出

text:

where r u
y dont u send me a pic 
k thk l8r

4. 结果

【引用】

1. 代码
   https://github.com/thefistlei/cplusprimer/blob/main/cprimer/cprimer/wordTransform.h

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