An Introduction to Programming with C++

Fifth Edition Chapter 13 Sequential Access Files

Objectives • 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 An Introduction to Programming with C++, Fifth Edition 2

Objectives (continued) • Test for the end of a sequential access file • Close a sequential access file • Read information from and write information to a sequential access file in .NET C++ An Introduction to Programming with C++, Fifth Edition 3

Concept Lesson • File Types • Using Sequential Access Files • Creating and Opening a Sequential Access File • Determining whether a File was Opened Successfully An Introduction to Programming with C++, Fifth Edition 4

Concept Lesson (continued) • Writing Information to a Sequential Access File • Reading Information from a Sequential Access File • Testing for the End of a Sequential Access File • Closing a Sequential Access File An Introduction to Programming with C++, Fifth Edition 5

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 An Introduction to Programming with C++, Fifth Edition 6

Using Sequential Access Files • A

sequential access file

is often called a

text file

An Introduction to Programming with C++, Fifth Edition 7

Using Sequential Access Files (continued) An Introduction to Programming with C++, Fifth Edition 8

Creating and Opening a Sequential Access File • You must create the input and output file objects used in a program – #include • ifstream and ofstream classes – using std::ifstream; and using std::ios; An Introduction to Programming with C++, Fifth Edition 9

Creating and Opening a Sequential Access File (continued) An Introduction to Programming with C++, Fifth Edition 10

Creating and Opening a Sequential Access File (continued) An Introduction to Programming with C++, Fifth Edition 11

Creating and Opening a Sequential Access File (continued) An Introduction to Programming with C++, Fifth Edition 12

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 An Introduction to Programming with C++, Fifth Edition 13

Determining whether a File was Opened Successfully (continued)

!

is the

Not logical operator

An Introduction to Programming with C++, Fifth Edition 14

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 An Introduction to Programming with C++, Fifth Edition 15

Writing Information to a Sequential Access File (continued) An Introduction to Programming with C++, Fifth Edition 16

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 An Introduction to Programming with C++, Fifth Edition 17

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’) An Introduction to Programming with C++, Fifth Edition 18

Reading Information from a Sequential Access File (continued) An Introduction to Programming with C++, Fifth Edition 19

Testing for the End of a Sequential Access 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 An Introduction to Programming with C++, Fifth Edition 20

Testing for the End of a Sequential Access File (continued) An Introduction to Programming with C++, Fifth Edition 21

Closing a Sequential Access File • To prevent the loss of data, close a sequential access file as soon as program finishes using it An Introduction to Programming with C++, Fifth Edition 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 An Introduction to Programming with C++, Fifth Edition 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 • Use close() to close a file – Failing to close an open file can result in loss of data An Introduction to Programming with C++, Fifth Edition 24

Application Lesson: Using a Sequential Access File in a C++ Program • Lab 13.1: Stop and Analyze • Lab 13.2

– Program should allow flower shop owner to save in a text file each salesperson’s name and sales amount • Also, display the total of the sales amounts in file • Lab 13.3

– Modified program will allow the user to display contents of sales.txt file • Lab 13.4: Desk-Check Lab • Lab 13.5: Debugging Lab An Introduction to Programming with C++, Fifth Edition 25