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Processing the Content of Files

Processing characters within a file.

Setup input and output files:-
     ifstream file_in ("myInputFile.txt");
     if (!file_in)
     {
          cout << "unable to access input file\n";
          exit (1);
     }
 
     ofstream file_out ("myOutputFile.txt");
     if (!file_out)
     {
          cout << "unable to access output file\n";
          exit (1);
     }
Go through the file, process it and output it:-
      while (file_in)
     {
          file_in.get (ch);
                      |
                  process characters
                      |
          file_out.get (ch);
     }
Close files:-
      file_in.close();
      file_out.close();
 

Processing lines and words in a file.

To set the program to the start of the file:

     if ( fseek( my_file, 0, 0 ) !=0 )
     {
          printf( "Can't move pointer to start." );
     }

To read a line having a maximum number of characters given in constant LINE_SIZE:

     fgets( line_read, LINE_SIZE-1, my_file );

To read in words on a line:

     sscanf( line_read, "%s %s %s etc.", first_word, second_word, third_word etc. );

String Operation Example:
  To find word "begin" at the start of a line in a file called masterpiece:

     if ( fseek( masterpiece, 0, 0 ) !=0 )    /* Goto to start of file */
     {
          printf( "Can't move pointer to start." ); return;
     }

     while( found_flag == 0 )
     {
          fgets(line_read, LINE_SIZE-1 ,masterpiece);
          sscanf(line_read, "%s", first_word);       /* Take first word */
          if (( strcmp ( first_word, "begin" ) == 0 ) || ( strcmp( first_word, "BEGIN" ) == 0 ))
          {
               found_flag = 1;
          }
     }
 

Allocate Memory for a Buffer

You need to allocate memory when copying data to a buffer or you will copy data to a null pointer.
To copy a string to a buffer:
     char *buffer;
    
     buffer = new char[50];             // Allocate some memory for the buffer.
     strcpy(buffer, "Hello there.");
 
 

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(c) Compiled by A J & B V Wood.

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