End-of-file tests and looping code March 16, 2006
1
End
End-
-of
of-
-file Tests and Looping
file Tests and Looping
Summary
Summary
Larry Caretto
Computer Science 106
Computing in Engineering
and Science
March 16, 2006
2
Outline
• Review looping code
• End-of-file tests
– Files as objects
– Functions associated with file names
• .good(), .fail() and .eof()
– Sentinels versus end-of-file functions
• Practice writing loops
3
Review Previous Material on Files
• File input/output
– Have to use #include <fstream> library
– Associate a program file name with an
operating system file name
•ifstream inFile( “input.dat” );
– Use program file name in place of cin
•inFile >> x >> y;
– Want to be able to have computer find end
of large data file
• Ca n use “sentinel” (data item that is not dat a) to
mark end of data stream
• Alternative is end-of-file test
4
File Names and Properties
• Program file names are objects
– Object-oriented programming
– Objects have functions that operate on
specific objects (e.g. ifstream inFile)
– Usual format is <object name>.<function>
– For the declaration ifstream inFile the
following functions are applicable
• inFile.good() is true if previous reads have not
found an error or an end of file
• in File.fail() is true if a read attempt failed
• inFile.eof() is true if an end of file is found
5
Testing for End of File <EOF>
• Consider effects of three separate
functions: .good(), .fail() and .eof()
– .good() is true if a future read statement
may be possible (no error or end of file
found yet)
– .fail() is true if a read statement could not
be completed (some variables not read)
– .eof() is true if an end of file is found
• Where is the eof located?
– Important to understand EOF test
6
Possible <EOF> Locations
Example 1: 12 14 -23.2<EOF>
Example 2: 12 14 -23.2 <EOF>
Example 3: 12 14 -23.2<newline>
<EOF>
• Example 1 file is saved immediately
after the last digit is entered
• Example 2 file has spaces (but no new-
line after the last digit
• Example 3 file has <newline> (and
possible spaces) after last digit
