c++ prime 5 ex11_4

代碼如下

// ex11_4_word_transform.cpp : 定義控制臺應用程序的入口點。
//

#include "stdafx.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;

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
    }
}

int main(int argc, char **argv)
{
    // open and check both files
    //if (argc != 3)
    //    throw runtime_error("wrong number of arguments");

    argv[1] = "……";
    argv[2] = "……";
    ifstream map_file(argv[1]); // open transformation file 
    if (!map_file)              // check that open succeeded
        throw runtime_error("no transformation file");

    ifstream input(argv[2]);    // open file of text to transform
    if (!input)                 // check that open succeeded
        throw runtime_error("no input file");

    word_transform(map_file, input);

    system("pause");

    return 0;  // exiting main will automatically close the files
}

關於main函數中的三個參數 ，ref: int main(int argc,char* argv[])詳解

讀寫文件，ref:C++文件讀寫詳解（ofstream,ifstream,fstream）

用cmd執行

argv[1]是exe的轉義字符路徑，argv[2]是 rules文件的轉義字符路徑，argv[3]是待轉換文件的轉義字符路徑。

C++ 編寫的解碼器小程序 map