C Overview, Part II (continued)

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C Overview, Part II(continued)
Reference Chapter 2, Sections 2.2-2.9
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Function Calls and Argument Passing

• Passing by value vs. passing by reference
  (address)
• C example
• int a 5, b 10
• swap(a, b) // function call
• void swap(int a, int b)
• int temp a
• a b
• b temp

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Function Calls and Argument Passing (continued)

• C supports reference parameters
• C example
• int a 5, b 10
• swap(a, b) // function call -- no
  addresses!
• void swap(int a, int b)
• int temp a
• a b
• b temp
• No dereferencing of formal parameters is
  necessary

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Inline Functions

• A function can have the code for its body
  included with
• its prototype
• Example
• inline int max(int a, int b) return(a gt
  b ? a b)
• Each function call is expanded by the compiler
• Increases code efficiency
• No guarantee that the compiler will do the
  expansion
• Use only for very small (single statement)
  functions

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Command-line Arguments

• The main function can receive arguments when
  invoked
• Implemented as follows
• int main(int argc, char argv)
• where argc number of command line
  arguments,
• including command line
  name (default 1)
• argv0 pointer to command line
  name as string
• argvn pointer to command line
  argument as string
• Example
• lowercase input.dat output.dat //
  lowercase program in text

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Vector Class Example
// File Vector.h class Vector public
Vector() //
default constructor Vector(float a, float
b) // constructor overloaded
Vector operator-(Vector a) // operating
overloading float inner(Vector a)
// vector inner product int nonzero()
// host vector nonzero
void display() // displays
host vector private float x
// vector x-coordinate float y
// vector y-coordinate
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Vector Class Example (continued)
// File Vector.C include Vector.h include
ltiostream.hgt VectorVector(float a, float b)
// constructor overloaded x a y
b Vector Vectoroperator -(Vector a) //
operator overloading Vector tmp tmp.x x
- a.x tmp.y y - a.y return(tmp)
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Vector Class Example (continued)
float Vectorinner(Vector a) return(x a.x
y a.y) int Vectornonzero()
return(x ! 0.0 y ! 0.0) void
Vectordisplay() cout ltlt ( ltlt x ltlt ,
ltlt y ltlt )
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Default Constructors

• A constructor with no arguments is called a
  default
• constructor.
• Usually used to set the attributes equal to
  default values
• VectorVector()
• a b 0.0
• If a class has no constructors, a default
  constructor that
• does nothing is supplied automatically.
• If a class defines any constructor, no default
  constructor
• is automatically supplied. The appropriate
  user-supplied
• constructor will be invoked upon object
  instantiation.

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Operator Overloading

• Predefined operators can be extended to
  operate on different
• types of operands. This is called operator
  overloading.
• Some consider this a type of polymorphism
• Example
• Vector Vectoroperator -(Vector a)
  // overloading minus
• Vector tmp
• tmp.x x - a.x tmp.y y - a.y
• return(tmp)
• The minus operator now works with Vector
  objects
• u v.operator - (w) OR u v - w
• where u, v, and w are all of type
  Vector

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C I/O Streams

• fstream is a predefined class in ltfstream.hgt
• fstream represents a stream I/O class
• General format
• fstream stream-name(disk-filename,
  mode)
• Examples
• fstream inData(mydata, iosin)
• fstream outData(results, iosout)
• inData gtgt x // read a value from
  input file
• outData ltlt x // send value to
  output file
• inData.close() // done by default on
  some systems
• outData.close() // done by default on
  some systems

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Error Handling

• Catch all errors that you can!
• cerr is a predefined output stream used for
  error messages
• Example
• fstream myin(file, iosin)
• if (myin.fail()) // fail is a member
  function of fstream
• cerr ltlt Cant open ltlt file ltlt
  \n
• exit(1) // terminates execution
• Usually want to terminate execution and give
  the user a
• meaningful error message for debug purposes.
  Use exit
• function from ltstdlib.hgt.

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Student Exercise

• Copy the code for program lowercase.C (pp.
  67-68) from
• the diskette in your text.
• Make the following correction before running
• cerr ltlt Usage lower infile outfile\n
  //incorrect
• cerr ltlt Usage ltlt argv0 ltlt infile
  outfile\n
• Create an appropriate input file.
• Run the program with no arguments, one
  argument
• (error), two arguments, and three arguments
  (error).

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