COMP102 Session 3A

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COMP102 Session 3A

• Lab07 Score Management Gadget

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File I/O

• File
• External collection of data
• Provided input to a program
• Stored output from a program
• Stored on secondary storage permanently
• Must be
• Opened before used
• Closed after used
• File I/O
• Operation related to file

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Stream

• Sequence of characters
• ltiostreamgt user interactive
• cin
• Input stream associated with keyboard
• cout
• Output stream associated with display
• ltfstreamgt file operation
• ifstream
• Defined input stream associated with file
• ofstream
• Defined output stream associated with file

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File Stream

• Before
• Getting data from a file
• Output data to a file
• Declare a stream object
• Creating a channel
• Associate this stream object to the file
• Connecting the stream component to the file with
  program

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File Stream

• E.g.

include ltfstreamgt ifstream fin fin.open("fil
ename.txt") // connects stream fsIn to the
external // file "filename.txt" fin.close() //
disconnects the stream and associated file
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Input File

• Include the ltfstreamgt
• include ltfstreamgt
• Declare an input stream object
• ifstream fin
• Open an dedicated file
• fin.open(filename.txt)
• Get character from file
• fin.get(character)
• Close the file
• fin.close()

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Output File

• Include the ltfstreamgt
• include ltfstreamgt
• Declare an output stream object
• ofstream fout
• Open an dedicated file
• fout.open(filename.txt)
• Put character from file
• fout.put(character)
• Close the file
• fout.close()

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File I/O Function

• Input file
• fin.eof()
• Test for end-of-file condition
• fin.get(char character)
• Obtains the next character from the file stream
• Put into the variable character
• Output file
• fout.put(char character)
• Inserts character to the output file stream

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File I/O More Function

• E.g.

ifstream fin char character
fin.open(data.txt) // open the file
fin.get(character) // get the first char
while(!fin.eof()) // loop to read each
character fin.get(character)
fin.close()
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Stream Manipulators

• Used to manage the input and output format of a
  stream
• With the directive ltiomanipgt
• E.g.
• cout ltlt endl
• cout ltlt hex
• cout ltlt setw(5)

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Stream Manipulators

• include ltiomanipgt
• setprecision(d)
• Set number of significant digits to d
• setw(w)
• Set field width to w
• setfill(c)
• Set fill character to c
• setiosflags(f)
• Set flag f to 1
• resetiosflags(f)
• Set flag f to 0

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Stream Manipulators

• E.g.

int a 1234567 int b 10 cout ltlt hex
ltlt a ltlt endl cout ltlt setiosflags(iosshowpos)
ltlt b ltlt endl cout ltlt resetiosflags(iosshowpos
) cout ltlt setiosflags(iosscientific) ltlt b
ltlt endl
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SUMMARY

• By the end of this lab, you should be able to
• Read/Write/Manipulate file with directive
• ltfstreamgt
• Formatting input and output stream with directive
• ltiomanipgt