Class 10: The Command Line

Held: Monday, 13 September 2010

Summary: We consider how and why one accesses the command line in C programs.

Related Pages:

• EBoard.
• Lab: The Command Line in C.
• Reading: K&R 5.10.

Notes:

• Are there questions on assignment 3?
• Readings for Tomorrow: A Tutorial on Binary Numbers and K&R 2.6 and 6.9.
• We may not finish today's lab in class. I expect you to finish it on your own. (You need not do the extra problems.)
• I returned HW2 before class today. Let me know if you have questions on my comments. We'll talk a bit about a variety of issues.

Overview:

• Command-line basics.
• Using the command line.
• Lab.

Command Line Basics

• C was designed in conjunction with the Unix system.
• That means that as we write C programs, we should be able to write programs that process the command line.
• It's fairly straightforward.
• When we write a main function, we give it two additional parameters:
  • argc - argument count - an integer giving the number of words on the command line.
  • argv - argument vector - an array of strings giving the values on the command line.
• That is, we write

  int
  main (int argc, char *argv[])
  {
    ...
  } // main
  

Using the Command Line

• What can we do with the argument vector?
• Traditionally, we scan through the command line to set flags and values for our program. After scanning the command line, we use the results.
• We sometimes take our input from the command line. For example, q2l might take its input from the command line rather than prompting for it.

Lab

• Do the lab.
• Be prepared to reflect.
• Be prepared to finish it on your own.