1. Today’s Lecture I/O Streams Tools for File I/O
Console I/O
File I/O
Tools for File I/O
Sequential Access & Random Access to Files

2. Introduction Streams In C++ Special objects
Deliver program input and output
In C++
Console I/O is working with streams
File I/O is also working with streams

3. Streams Stream: A flow of data Input stream Output stream
Flow into program
Can come from keyboard
Can come from file
Output stream
Flow out of program
Can go to screen
Can go to file

4. Streams Usage We’ve used streams already cin cout
Input stream object connected to keyboard
cout
Output stream object connected to screen

5. Stream Example
int num1, num2, total; cout << "First number: "; cin >> num1; cout << "Second number: "; cin >> num2; total = num1 + num2; cout << “total = " << total << endl;

6. Streams Usage We’ve used streams already Can define other streams cin
Input stream object connected to keyboard
cout
Output stream object connected to screen
Can define other streams
To or from files
Used similarly as cin, cout

7. Streams Usage Examples: cin, cout
Consider:
Using the pre-defined stream cin int Number; cin >> Number;
Reads value from stream (keyboard), assigned to Number
Using the pre-defined stream cout cout << Number;
Writes value to stream (monitor)

8. Streams Usage Like cin, cout
Consider:
Given program defines stream inStream that comes from some file: int Number; inStream >> Number;
Reads value from stream (file), assigned to theNumber
Program defines stream outStream that goes to some file outStream << theNumber;
Writes value to stream, which goes to file

9. Files Reading from file Writing to file
When program takes input
Writing to file
When program sends output
Start at beginning of file (Sequential access)
Other methods available

10. File Connection Must first create a file stream object
Then connect the file to the file stream object
For input only:
File  ifstream object
For output only:
File  ofstream object
Classes ifstream and ofstream
Defined in library <fstream>
Named in std namespace

11. File I/O Libraries
To allow both file input and output in your program: #include <fstream> using namespace std;

12. Declaring Streams Objects (Variables)
Stream must be declared like any other class variable: ifstream input_file_stream; ofstream out_file_stream;
Must then "connect" to file: input_file_stream.open("infile.txt");
Called "opening the file"
Uses member function open
Can specify complete pathname

13. Streams Usage
Once declared and connected, use it like cin and cout!
int N;
input_file_stream >> N;
Output stream similar: ofstream output_file_stream; output_file_stream.open("outfile.txt"); output_file_stream << "Number = " << N;

14. Closing Files Files should be closed
When program completed getting input or sending output
Disconnects stream from file
In action: input_file_stream.close(); output_file_stream.close();

15. File Example: Display 12.1 Simple File Input/Output (1 of 2)

16. File Example: Display 12.1 Simple File Input/Output (1 of 2)

17. Appending to a File
Standard of stream open operation begins with empty file
Even if file exists  contents lost
Open for append: ofstream outStream; outStream.open("important.txt", ios::app);
If file doesn’t exist  creates it
If file exists  appends to end

18. Compare Console I/O and File I/O
All cin functions are same for files!
Read in (send out) integers (int)
Read in (send out) characters (char)
Read in (send out) floating-point s (float) ….
For String operating:
>> read one word (separated by spaces, new lines)
getline() read one line of words

19. Compare Console I/O and File I/O (continued)
For console String (C-string) operations
char S[100];
cin >> S;
read one word
cin.getline(S, 20) ;
read one line of words

20. Compare Console I/O and File I/O (continued)
For file String (C-string) operations
ifstream ifm; ifm.open("infile.txt");
char S[100];
ifm >> S;
read one word
ifm.getline(S, 20) ;
read one line of words

21. Compare Console I/O and File I/O (continued)
cout is same for file operations (say fout)
ofstream fout;
fout.open(“output.txt", ios::app);
cout << “whatever\n”
fout << “whatever\n”
Whatever displayed on screen will be same as those saved in file

22. More I/O member functions
See Appendix 4 of the textbook
Stream_var.open(“File name”);
Stream_var.close();
Strean_var.eof();
Stream_var.get(char_var);
Stream_var.getline(cstring_var, length);

23. Checking End of File Use loop to process file until end
An extraction operator actually returns a boolean value inStrem >> next
Return true if the read was successful (space and new line will not be read) and returns false when code attempts to read beyond the end of the file
Int next, sum =0;
while (inStream >> next)
{ sum = sum + next; }
cout << “ the sum is “ << sum << endl;

24. Checking End of File Use loop to process file until end
inStrem.get(next)
Return true if the read was successful and returns false when code attempts to read beyond the end of the file
char next, sum =0;
while (inStream.get(next))
{ sum = sum + 1; }
cout << “ the total number of characters is “ << sum << endl;

25. Checking End of File Use loop to process file until end
inStrem.getline(next, length)
Return true if the read was successful and returns false when code attempts to read beyond the end of the file
Char[] next, sum =0;
while (inStream.getline(next, 100))
{ sum = sum + 1; }
cout << “ the total number of lines is “ << sum << endl;

26. Which Function to Write
The easiest one and works for any text data
<<

27. Which Function to Read
Numbers (Integer / floating-point) file: numbers are separated by blank space(s)
>>
Text file: words are separated by blank space(s): each word is going to be processed separately

28. Which Function to Read (continued)
Character files
each character (including space) needs to be processed individually
get(char s)
Ignore spaces, new lines, and tab
>>
Character files: one line is a record
getline(char s[], int size)

29. Tools: File Names as Input
Stream open operation
Argument to open() is string type
Can be literal (used so far) or variable char fileName[16]; ifstream inStream; cout << "Enter file name: "; cin >> fileName; inStream.open(fileName);
Provides more flexibility

30. File Access Applications
Copy files
Copy char by char
Copy line by line
Process files:
Determine how many specific characters
Count words
Count lines
Work on numbers

31. Read and Write can be Performed at the Same Time
Opens same as istream or ostream
Adds second argument
fstream rwStream; rwStream.open("stuff", ios::in | ios:: out);
Opens with read and write capability
It is confusing where to read and where to write: not recommend to use.

32. Random Access to Files Sequential Access Random Access
Most commonly used
So far we have talked about
Random Access
Rapid access to records
Access "randomly" to any part of file

33. Random Access Tools Move about in file rwStream.seekp(1000);
Positions put-pointer at 1000th byte
rwStream.seekg(1000);
Positions get-pointer at 1000th byte
Not a requirement for this course

34. Summary of File Operations
Read from a file
Write to a new or existing file
Delete a file
Copy a file
Move a file
Modify a file