File I/O Review:

• declare file stream object
• ifstream infile;     // for file input - reading
• ofstream outfile;  // for file output - writing
• fstream file;   // this wll allow for reading or writing to the attached file.
• open file
• infile.open("filename.ext");
• can delcare and open at same time
• ifstream infile("filename.ext");
• read from or write to file
• infile >> variablename;
• outfile << variablename;
  
• close file
• infile.close();

---

Some Open  mode  Indicators

ios::app    new data written to the file is always appended to the end of the file.
EX:    outfile.open("results.dat",ios::app)   

ios::trunc    when the file  is opened, if it exists all current data in it is deleted.  (default if
                    ios::out is specified  and ios::ate, ios::app, and ios::in are not specified)

ios::ate        when the first byte of data is written to the file, it is appended to the end, but
                    subsequent bytes are written, to the current position

ios::nocreate    if the file does not already exist, the function fails   (good to check for  input file existence)
EX:    infile.open("data.txt",ios::nocreate)        //if you can't find it don't create one
         outfile.open("results.txt",ios:app|ios::nocreate)  // open output file to append new output to bottom of file, don't create one if can't find
         
ios::noreplace    if the file already exists, the function fails.  (good if you  want to make sure you don't overwrite  exisiting output file)

ios::binary        opens the file in binary mode (the default is text mode)

---

Checking for successful connection to a file

infile.open("filename");
if (infile.fail())                 // did the file fail to open?
{
    cout<< "failed to open file"<<endl;


Note:    the statement    infile.open("filename") on its own will create a file if one doesn't exist already
This is great for output files but we expect that our input files have some data in the them for reading
To check that the input file exists prior to your trying to open it:

    infile.open("filename", ios::nocreate);  // try to open the input file - don't create a new one if it's not found
    if (infile.fail())        // was the input file found?       
        cout << "Input file not found" << endl;

---

Some  "Methods" for  stream I/O

get(character-variable)
    ex:    infile.get(i)        will get the next character from the input stream and place it in variable i

getline(string var, int n, '\n')    extract characters from the input stream until either n-1 characters
                                                are read or a newline is encountered
    ex:    infile.getline(phrase,max,'\n')

peek(character-variable)    place the next character  from the input stream  in variable i  put do not
                                            extract that character from the stream - leave it there
    ex:    infile.peek(x);        // will place the next character from the input stream in variable x put also keep
                                            it in the input stream as well

put(character-variable)        put a single character  on the output stream
    ex:    outfile.put(x)        // will place the character in variable x on the output stream

eof()                                returns true if a read  is attempted past the EOF (end-of-file)
    ex:    infile.eof()            // if we are at EOF it will return true otherwise false

ignore(int n)                    Skip over the next n characters  in the stream .  Good if you know you
                                        exactly how much  character data you can ignore (jump over)
    ex:    infile.ignore(10)    // will skip the next 10 characters in the input file stream

    ex:    infile.ignore()        // will skip over the next 1 character in the input file stream

NOTE:    none of these functions skips white space

---

Remember:   
    manipulators - looked at earlier - setw, setprecision etc hold for file i/o.

    The file format of a file should never be a mystery to you as a programmer.  You must define or be given a file format telling you how the
data will  be  presented in the file.  Your job is to read the data given a specific format.  You cannot  and do not have to guess as to the format.

---

Text File    -- all examples we are working with to date are text files.

    Contains characters coded to the ASCII code (or another if using another platform)
     You can read the file - it is text
     It has a line structure
        consists of a  number of lines
        each line with an arbitrary  number of characters and is terminated with an end of line ('\n'}

Binary File
    does not contain ASCII coded characters
    An example would be an executable file

    No line structure, only a sequence of bytes
    No data conversion,  read bytes, write bytes