Streams, Files, and Formatting

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Streams, Files, and Formatting

• Standard Input/Output Streams
• External Files
• More on Reading String Data
• Input/Output Manipulators
• Common Programming Errors

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8.1 Standard Input/Output Streams

• Stream is a sequence of characters
• Working with cin and cout
• Streams convert internal representations to
  character streams
• gtgt input operator (extractor)
• ltlt output operator (inserter)
• Streams have no fixed size

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Reading Data gtgt

• Leading white space skipped
• ltnwlngt also skipped
• Until first character is located
• cin gtgt ch
• Also read character plus white space as a
  character
• get and put functions

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CountChars.cpp

• // File CountChars.cpp
• // Counts the number of characters and lines in
• // a file
• include ltiostreamgt
• include ltstringgt
• using namespace std
• define ENDFILE "CTRL-Z"

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CountChars.cpp

• int main()
• const char NWLN '\n' // newline character
• char next
• int charCount
• int totalChars
• int lineCount
• lineCount 0
• totalChars 0

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CountChars.cpp

• cout ltlt "Enter a line or press " ltlt ENDFILE ltlt
• " "
• while (cin.get(next))
• charCount 0
• while (next ! NWLN !cin.eof())
• cout.put(next)
• charCount
• totalChars
• cin.get(next)
• // end inner while

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CountChars.cpp

• cout.put(NWLN)
• lineCount
• cout ltlt "Number of characters in line " ltlt
• lineCount ltlt " is " ltlt charCount ltlt endl
• cout ltlt "Enter a line or press " ltlt
• ENDFILE ltlt " "
• // end outer while
• cout ltlt endl ltlt endl ltlt
• "Number of lines processed is " ltlt
• lineCount ltlt endl

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CountChars.cpp

• cout ltlt "Total number of characters is " ltlt
• totalChars ltlt endl
• return 0

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8.2 External Files

• Batch
• Requires use of data files (save to disk)
• Batch can be run during off peak use
• allows things to be complete at start of day
• Interactive
• Real time systems
• Ok for smaller programs
• Programs that complete quickly

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Files

• Naming
• .cpp .dat .out .in
• How to attach files to the stream
• stream object
• external file name
• internal name
• open
• Additional functions as part of fstream.h class

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Files

• Declare the stream to be processed need to
  include fstream
• ifstream ins // input stream
• ofstream outs // output stream
• Need to open the files
• ins.open (inFile)
• outs.open (outFile)

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Files

• define associates the name of the stream with
  the actual file name
• fail() function - returns true nonzero if file
  fails to open
• Program CopyFile.cpp demonstrates the use of the
  other fstream functions
• get , put, close and eof
• discuss program

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CopyFile.cpp

• // File CopyFile.cpp
• // Copies file InData.txt to file OutData.txt
• include ltcstdlibgt
• include ltfstreamgt
• using namespace std
• // Associate stream objects with external file
• // names
• define inFile "InData.txt"
• define outFile "OutData.txt"

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CopyFile.cpp

• // Functions used ...
• // Copies one line of text
• int copyLine(ifstream, ofstream)
• int main()
• // Local data ...
• int lineCount
• ifstream ins
• ofstream outs

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CopyFile.cpp

• // Open input and output file, exit on any
• // error.
• ins.open(inFile)
• if (ins.fail ())
• cerr ltlt " ERROR Cannot open " ltlt
• inFile ltlt " for input." ltlt endl
• return EXIT_FAILURE // failure return
• // end if

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CopyFile.cpp

• outs.open(outFile)
• if (outs.fail())
• cerr ltlt " ERROR Cannot open " ltlt
• outFile ltlt " for output." ltlt endl
• return EXIT_FAILURE // failure return
• // end if
• // Copy each character from inData to outData.
• lineCount 0
• do

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CopyFile.cpp

• if (copyLine(ins, outs) ! 0)
• lineCount
• while (!ins.eof())
• // Display a message on the screen.
• cout ltlt "Input file copied to output file." ltlt
• endl
• cout ltlt lineCount ltlt " lines copied." ltlt endl
• ins.close()
• outs.close()
• return 0 // successful return

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CopyFile.cpp

• // Copy one line of text from one file to another
• // Pre ins is opened for input and outs for
• // output.
• // Post Next line of ins is written to outs.
• // The last character processed from
• // ins is ltnwlngt
• // the last character written to outs
• // is ltnwlngt.
• // Returns The number of characters copied.
• int copyLine (ifstream ins, ofstream outs)

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CopyFile.cpp

• // Local data ...
• const char NWLN '\n'
• char nextCh
• int charCount 0
• // Copy all data characters from stream ins to
  
• // stream outs.
• ins.get(nextCh)
• while ((nextCh ! NWLN) !ins.eof())
• outs.put(nextCh)
• charCount

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CopyFile.cpp

• ins.get (nextCh)
• // end while
• // If last character read was NWLN write it
• // to outs.
• if (!ins.eof())
• outs.put(NWLN)
• charCount
• return charCount
• // end copyLine

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CopyFile.cpp

• Program Output
• Input file copied to output file.
• 37 lines copied.

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File Processing

• Loop processing
• for loops
• while loops
• Newline character
• eof() function returns a False if file is not
  empty
• while ( ! ins.eof())
• do stuff

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8.3 Using External File Functions

• Payroll Case Study
• Two programs process the payroll
• Design Process
• Problem Analysis
• Program Design
• Program Implementation
• Program Verification and Test

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Payroll Case Structure Chart
processEmp
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ProcessEmp Structure Chart
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Payroll.cpp

• // File Payroll.cpp
• // Creates a company employee payroll file
• // computes total company payroll amount
• include ltfstreamgt
• include ltcstdlibgt
• include "money.h"
• include "money.cpp"
• using namespace std

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Payroll.cpp

• // Associate streams with external file names
• define inFile "EmpFile.txt" // employee file
• define outFile "Salary.txt" // payroll file
• // Functions used ...
• // PROCESS ALL EMPLOYEES AND COMPUTE TOTAL
• money processEmp(istream, ostream)
• int main()
• ifstream eds
• ofstream pds
• money totalPayroll

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Payroll.cpp

• // Prepare files.
• eds.open(inFile)
• if (eds.fail ())
• cerr ltlt " ERROR Cannot open " ltlt inFile
• ltlt " for input." ltlt endl
• return EXIT_FAILURE // failure return
• pds.open(outFile)
• if (pds.fail())

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Payroll.cpp

• cerr ltlt "ERROR Cannot open " ltlt outFile
• ltlt " for output." ltlt endl
• eds.close()
• return EXIT_FAILURE // failure return
• // Process all employees and compute total
• // payroll.
• totalPayroll processEmp(cin, cout)
• // Display result.
• cout ltlt "Total payroll is " ltlt totalPayroll ltlt
• endl

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Payroll.cpp

• // Close files.
• eds.close()
• pds.close()
• return 0

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Payroll.cpp

• // Insert processEmp here.
• // Process all employees and compute total
• // payroll amount
• // Pre eds and pds are prepared for
• // input/output.
• // Post Employee names and salaries are
• // written from eds to pds
• // and the sum of their salaries is returned.
• // Returns Total company payroll
• money processEmp (istream eds, ostream pds)

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Payroll.cpp

• string firstName
• string lastName
• float hours // input hoursWorked
• money rate // input hourly rate
• money salary // output gross salary
• money payroll // return value - total
  company payroll
• payroll 0.0
• // Read first employee's data record.
• eds gtgt firstName gtgt lastName gtgt hours gtgt rate

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Payroll.cpp

• while (!eds.eof())
• salary hours rate
• pds ltlt firstName ltlt lastName ltlt salary ltlt
• endl
• payroll salary
• // Read next employee's data record.
• eds gtgt firstName gtgt lastName gtgt hours gtgt
• rate
• // end while
• return payroll
• // end processEmp

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PayrollFile.cpp

• Program Output
• Total payroll is 677.38

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8.4 More on Reading String Data

• Getline - could be used to process an entire line
  of data
• Use as a delimiter character
• getline (eds, name, )
• Advance the newline
• getline (eds, name, \n)
• Use care when choosing cin, get or getline

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8.5 Input/Output Manipulators

• Chapter 5 covered setf, unsetf, precision and
  width
• Can be used with the cout and ltlt
• Table 8.3 lists various manipulator functions
  (setiosflags, setprecision, setw)
• include iomanip when using
• Can be used with external files like stdout and
  stdin

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Formatting with State Flags

• Depending on the setiosflags or unsetiosflags
• Output can be controlled by other format state
  flag
• Flags are enumerated types
• iosflagname
• Table 8.3 lists some flags
• boolalpha, fixed, left, right, showpoint etc

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8.6 Common Programming Errors

• Connecting streams and external files
• Declare stream object and open the file
• Watch use of while loops when processing
• Test values see what you actually have
• Reading past the eof
• White space
• Newline character
• Formatting via flags