1. Computer Programming TCP1224 Chapter 13 Sequential File Access

2. Objectives File types Open a sequential access file Determine whether a file was opened successfully Write data to a sequential access file Read data from a sequential access file Test for the end of a sequential access file Close a sequential access file 2

3. File Types A program can “read” from or “write” to a file ▫Files to which information is written are output files ▫Files that are read by the computer are input files Types of files in C++ ▫Sequential  Information is accessed in consecutive order ▫Random  Can be accessed in consecutive or in random order ▫Binary  Information can be accessed by its byte location 3

4. Using Sequential Access Files A sequential access file is often called a text file 4

5. Using Sequential Access Files (continued) 5

6. Creating and Opening a Sequential Access File You must create the input and output file objects used in a program ▫ #include  For ifstream and ofstream classes (see next slide) ▫ using std::ifstream; and using std::ios; 6

7. Creating and Opening a Sequential Access File (continued) 7

8. 8 Default Conceptually similar to the >> and >

9. Creating and Opening a Sequential Access File (continued) 9

10. Determining whether a File was Opened Successfully open() may fail when attempting to open a file ▫E.g., it will not be able to create an output file when the path in fileName does not exist, or when the disk is full 10

11. Determining whether a File was Opened Successfully (continued) 11 ! is the Not logical operator

12. Closing a Sequential Access File In most programming sequence, after a “handle” is open, it needs to be close. Handle can be file (in this case), network or other devices. To prevent the loss of data, close a sequential access file as soon as program finishes using it 12

13. Skeleton Code for File Access #include using namespace std; ifstream inputFile; ofstream outputFile; int main() { inputFile.open("myinput.txt"); // This is the same as inputFile.open("myinput.txt", ios::in); if (inputFile.is_open()) { cout << "Input file successfully open" << endl; inputFile.close(); } else cout << "Input file cannot be opened" << endl; 13

14. Skeleton Code for File Access (Con’t) outputFile.open("myoutput.txt", ios::out); if (outputFile.is_open()) { cout << "Output file successfully open" << endl; outputFile.close(); } else cout << "Output file cannot be opened" << endl; } 14

15. Writing Information to a Sequential Access File Field: single item of information about a person, place, or thing ▫E.g., a name, a salary, a SSN, or a price Record: a collection of one or more related fields ▫Contains data about a specific person, place, or thing ▫The college you are attending keeps student records  Examples of fields include your SSN, name, address, phone number, credits earned, and grades earned 15

16. Writing Information to a Sequential Access File (continued) 16

17. Writing Information to a Sequential Access File (continued) To verify if information was written correctly, open the (sequential access) file in a text editor ▫E.g., the text editor in Visual C++ or Notepad 17

18. Reading Information from a Sequential Access File Use >> to read char and numeric data from a file Use getline() to read string data from a sequential access file ▫The default delimiter character is the newline character (‘\n’) 18

19. Reading Information from a Sequential Access File (continued) 19

20. Testing for the End of a Sequential Access File We need to know when we have reached the end of the file. A file pointer keeps track of the next character either to read from or write to a file ▫When a sequential access file is opened for input, the file pointer is positioned before the first character ▫As characters are read, the pointer is moved forward 20

21. Testing for the End of a Sequential Access File (continued) 21

22. Summary Sequential access files can be input or output files To use a text file, program must contain: ▫ include directive ▫ using std::ios; statement Use the ifstream and ofstream classes to create input and output file objects, respectively Use is_open() to determine whether a text file was opened successfully Use close() to close a file ▫Failing to close an open file can result in loss of data 22

23. Summary (continued) Records in a text file are usually written on a separate line in the file ▫Use endl eof() determines if file pointer is at end of the file 23