What is a command line argument and what is its uses?

Answer 1

Back in the days of MSDOS, before Windows, programs were run not in a graphical shell but in a text-mode command-line environment. The name of the program was typed in, and then the user would press ENTER to run the program.

Borrowing from Unix and CP/M systems, programs were given the option of having parameters sent to them - a list separated by spaces after the filename and a space, but before ENTER was pressed. This gave users the opportunity to tell the program how to run.

Windows still uses this system for passing information to a program when it runs the program. The parameters are passed in the same way, but every programming language has its own method of reading them.

Under C, you'll have likely noticed that sometimes you start a program with the following:

int main(int argc, char **argv)

{

...

}

"argc" and "argv" are used by your program to get these parameters. "argc" contains the number of parameters, and "argv" contains the parameter list.

Because the name of your program is always supplied as the first parameter, "argc" will always be at least 1, and "argv[0]" will contain the filename of your program.

"argv" is a list of character arrays - a list of null-terminated strings. The following program will demonstrate how to access the parameters supplied to your program:

#include

int main(int argc, char **argv)

{

int count;

for (count=0; count

printf("Param %d: %s\n", count, argv[count]);

return 0;

}

If you compile this and then run it at the command line, it will display on each line the list of parameters you feed it. For instance, passing the string this is a "test that I've" written will display:

Param 0: (the full path of your program, including directory and filename)

Param 1: this

Param 2: is

Param 3: a

Param 4: test that I've

Param 5: written