Command Line Arugments Overview

Command Line Arguments

So far, all of our programs have begun pretty much the same way:

    int main(void)
    {

Since we've been collecting user input through in-program prompts, we haven't needed to modify this declaration of main.

If we want the user to provide data to our program before the program starts running, we need a new form.

To collect so called command-line arguments from the user, declare main as:

    int main(int argc, string argv[]) // the first parameter (argument/input) is an integer argc and the second is an array of strings.
    {

These two special arguments enable you to know what data the user provided at the command line and how much data they provided.

argc(argument count)

• This integer-type variable will store the number of command-line arguments the user typed when the program was executed.

command	argc
./greedy	1
./greedy 1024 cs50	3

• (greedy is the name of the program in the above example)

argv (argument vector)

• This array of strings stores, one string per element, the actual text the user typed at the command-line when the program was executed.

• The first element of argv is always found at argv[0] (first index of the argv array). The last element of argv is always found at argv[argc-1] (this is because the number of elements that exist in the array are argc number of elements).

Let's assume the user executes the greedy program as follows:

./greedy 1024 cs50

argv indices	argv contents
argv[0]	"./greedy"
argv[1]	"1024" (stored as a string NOT an integer)
argv[2]	"cs50"
argv[3]	??? (often leads to segmentation fault)