Command-line arguments

1
Command-line arguments

• CS 201 Fundamental Structures of Computer Science

2
Introduction

• A command-line argument is the information that
  follows the name of the program on the command
  line of the operating system
• Command-line arguments are used to pass
  information into a program when you run it
• They facilitate the use of your program in batch
  files
• They give a professional appearance to your
  program

3
Introduction

• C defines two built-in parameters to main()
• They receive the command line arguments
• Their names are argc and argv
• The names of the parameters are arbitrary.
  However, argc and argv have been used by
  convention for several years.
• They are optional

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int main( int argc, char argv )

• argc is an integer
• Holds the number of arguments on the command line
• Since the name of the program always corresponds
  to the first argument, it is always at least 1

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int main( int argc, char argv )

• argv is a pointer to an array of character
  pointers.
• Each character pointer in the argv array
  corresponds a string containing a command-line
  argument
• argv0 points the name of the program, argv1
  points to the first argument, argv2 points to
  the second argument,
• Each command-line argument is a string
• If you want to pass numerical information to your
  program, your program should convert the
  corresponding argument into its numerical
  equivalent
• Each command-line argument must be separated by
  spaces or tabs
• Commas, semicolons, and the like are not valid
  argument separators

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• include ltiostreamgt
• using namespace std
• int main( int argc, char argv )
• cout ltlt "Hello "
• for (int i 1 i lt argc i)
• cout ltlt argvi ltlt " "
• cout ltlt "! " ltlt endl
• return 0

cgunduz_at_knuth cgunduz g prog1.cpp o
exe_1 cgunduz_at_knuth cgunduz ./exe_1 Cigdem
Gunduz Hello Cigdem Gunduz ! cgunduz_at_knuth
cgunduz ./exe_1 Cigdem Gunduz Demir Hello
Cigdem Gunduz Demir !
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Passing numeric command-line arguments

• All command-line arguments are passed to the
  program as strings
• Your program should convert them into their
  proper internal format
• For that, C supports standard library functions
  most commonly used ones are
• atof() converts a string to a double and
  returns the result
• atoi() converts a string to a int and returns
  the result
• atol() converts a string to a long int and
  returns the result
• Each of these functions
• Expects a string containing a numeric value as an
  argument
• Uses the header ltcstdlibgt

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• include ltiostreamgt
• include ltcstdlibgt
• using namespace std
• int main( int argc, char argv )
• if (argc ! 4)
• cout ltlt "Usage \n\t"
• cout ltlt "1. Integer (0) or double (1)
  division\n\t"
• cout ltlt "2. Operand 1\n\t3. Operand 2\n\n"
• exit(1)
• if (atoi(argv1) 0)
• int a atoi(argv2)
• int b atoi(argv3)
• cout ltlt a ltlt "\\" ltlt b ltlt " " ltlt a / b ltlt
  endl
• else
• double a atof(argv2)
• double b atof(argv3)

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cgunduz_at_knuth cgunduz g prog2.cpp -o
exe_2 cgunduz_at_knuth cgunduz ./exe_2 Usage
1. Integer (0) or double (1) division
2. Operand 1 3. Operand 2 cgunduz_at_knuth
cgunduz ./exe_2 0 5 3 5\3
1 cgunduz_at_knuth cgunduz ./exe_2 1 5
3 5\3 1.66667 cgunduz_at_knuth cgunduz ./exe_2
0 8.2 2.9 8\2 4 cgunduz_at_knuth cgunduz
./exe_2 1 8.2 2.9 8.2\2.9 2.82759