Files

• This is just a quick review of the first part of chapter 4.
• Files in c++ are handled by input/output streams.
• As we know, these streams behave like cin and cout
  • Stream extraction/insertion operators (<< and >>)
  • getline, ignore
• All the stream manipulators we have learned work as well
  • setw, fixed, scientific, ...
• As we learned last time we need to include fstream
• The get function
  • Will will read the next character, regardless of value, from the stream.
• We sort of discussed this but we treat a stream as a boolean expression
  • If it evaluates to true, the last operation on the stream was successful
  • If it evaluates to false, the last operation was not successful.
• This is the only way you can detect things like the end of a file, successful read from a file, or even opening a file.
  • There are a set of fail bits
  • These tell us WHY the stream failed.
  • They are NOT predictors of the future.
• You know, but need to review how to read all data from a file.

  • ifstream inFile;
    
    inFile.open("filname");
    if (not inFile) {
        cout << "failed to open filename" << endl;
    } else {
        // operation to read in data on file.
        getline(line, inFile);
        while (inFile) {
            Process(line);
            getline(line, inFile);
        }
        inFile.close();
    } 

  Some additional items.
  • Open file streams must be passed by reference.
    • This makes sense, as the state of the stream needs to change.
  • You can have multiple files open at a time, just use different identifiers.
• One bad thing:
  • *nix and Windows have a small difference in text files that is annoying.
  • *nix ends a line with '\n'.
  • For some reason Windows ends with '\r\n'
  • getline will skip up to the \n -
    • that is the definition of getilne's default behavior.
    • And it only deals with one character in any case.
  • So string in a text file from windows will have an extra \r on the end.
• On many linux systems are a pair of utilities to deal with this.
  • dos2unix and unix2dos
  • On the *nix side od -c filename will show you file contents.
  • If you create your files on the Windows side, make sure you remove the \r characters.