Streams and Basic File IO

1. Streams and Basic File IO

2. Terms to Know • Stream • Input Stream • Output Stream • Reading • Writing • ifstream • ofstream • fstream • Connecting to a file • External file name • Close • Object • Member function • Class • Dot operator • Calling object • fail

3. Basic IO Terms • A stream is a flow of data • If the flow is into your program, the stream is called an input stream • If the flow is out of your program, the stream is called an output stream • Describe the streams that we have previously used

4. Why Use Files for IO? • Permanent Storage • Ability to re-use input • Convenient for large quantities of data

5. Basic FILE IO Terms • When your program takes input from a file, it is said to be reading from the file • When your program sends output to a file, it is said to be writing to the file • The method we use to read a file reads from beginning to end; you are not allowed to back up and read anything in the file a second time • Note: this is exactly how we read input from the keyboard • The same goes for writing to a file

6. Basic FILE IO Terms (cont.) • A stream is an object variable • To change the value of a stream variable (re-assign), we could disconnect a stream from one file and reconnect to another • You can’t reassign a stream using the assignment operator(=) like you can with a primitive data type • To allocate memory for a stream object, you must declare it • The type for input file stream variables is ifstream • The type for output file stream variables is ofstream • These types are in the library fstream • See Example 1: BasicFileIO

7. Basic FILE IO Terms (cont.) • Stream variables must be connected to a file • This is called opening a file • Use the open function to connect a stream variable to a file (See example) • This is done with both ifstream and ofstream objects • Once a stream is connected to a file, the extraction and insertion operators can be used in the same way as cin and cout • Note: When using open() with an ofstream, the function will create a new file if one does not already exist, and will empty the contents of files that do already exist • Every file should be closed when your program is finished reading from it or writing to it; a file is closed using the close() function

8. File Names • Note that the file name given as the argument to the open() funtion must be enclosed in quotations and include the file extension • This is called the external file name • This is the name used by the operating system • Once a stream is connected to a file, you will no longer refer to it by its external file name; you will use the name of the stream to refer to the file

9. Classes and Objects • An object is a variable that has functions as well as data associated with it • A function that is associated with an object is called a member function • A type whose variables are of type object is a class • A function is called using the dot operator • The object named before the dot is referred to as the calling object

10. Member Functions in ifstream and ofstream • open() • fail()

11. Formatting techniques: member functions used for formatting • setf: means to set flag • unsetf • precision • width

12. Manipulator Functions • A manipulator function is a function that is called in a non-traditional way • Manipulators are placed after an insertion operator • What manipulator function have we already worked with? • setw – manipulator that does the exact same thing as width() • setprecision – manipulator that does the exact same thing as precision() • To use either of these functions, you must include the iomanip library

13. Formatting Flags for setf