decomment.cpp

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#include <iostream>
#include <fstream>
#include <cstdlib>    // for exit
using namespace std;
#include "prompt.h"

// Owen Astrachan 7/4/1996, revised 5/4/99
// state-machine approach for removing all // comments from a file
// (doesn't handle // in a string, e.g., " test // comment "

class Decomment
{
  public:
    Decomment();
    void Transform(istream& input, ostream& output);
    
  private:
    void Echo(char ch, ostream& output);
    
    const char SLASH;
    const char NEWLINE;
    
    enum ReadState{TEXT, FIRST_SLASH, COMMENT};
};

Decomment::Decomment()
 : SLASH('/'),
   NEWLINE('\n')
{
    // constants initialized
}

void Decomment::Echo(char ch, ostream& output)
{
    output << ch;
}

void Decomment::Transform(istream& input, ostream& output)
{
    char ch;
    ReadState currentState = TEXT;
    while (input.get(ch))              // read one char at a time
    {   switch(currentState)
        {
          case TEXT:
            if (ch == SLASH)           // potential comment begins
            {   currentState = FIRST_SLASH;
            }
            else
            {   Echo(ch,output);
            }
            break;
            
          case FIRST_SLASH:
            if (ch == SLASH)
            {   currentState = COMMENT;
            }
            else                      // one slash not followed by another
            {   Echo(SLASH,output);   // print the slash from last time
                Echo(ch,output);      // and the current character
                currentState = TEXT;  // reading uncommented text
            }
            break;

          case COMMENT:
            if (ch == NEWLINE)          // end-of-line is end of comment
            {   Echo(NEWLINE,output);   // be sure to echo end of line
                currentState = TEXT;
            }
	        break;
        }
	 }
}

int main()
{  
    string filename = PromptString("enter filename: ");
    ifstream input(filename.c_str());
    if (input.fail())
    {   cout << "could not open " << filename << " for reading" << endl;
        exit(1);
    }
    Decomment dc;
    dc.Transform(input,cout);
    
    return 0;
}