Arguments to main in C [duplicate]

Question

I don't know what to do! I have a great understanding of C basics. Structures, file IO, strings, etc. Everything but CLA. For some reason I cant grasp the concept. Any suggestions, help, or advice. PS I am a linux user

Answer 1

The signature of main is:

int main(int argc, char **argv);

argc refers to the number of command line arguments passed in, which includes the actual name of the program, as invoked by the user. argv contains the actual arguments, starting with index 1. Index 0 is the program name.

So, if you ran your program like this:

./program hello world

Then:

• argc would be 3.
• argv[0] would be "./program".
• argv[1] would be "hello".
• argv[2] would be "world".

Answer 2

Imagine it this way

*main() is also a function which is called by something else (like another FunctioN)

*the arguments to it is decided by the FunctioN

*the second argument is an array of strings

*the first argument is a number representing the number of strings

*do something with the strings

Maybe a example program woluld help.

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

    printf("you entered in reverse order:\n");

    while(argc--)
    {
        printf("%s\n",argv[argc]);
    }

return 0;
}

it just prints everything you enter as args in reverse order but YOU should make new programs that do something more useful.

compile it (as say hello) run it from the terminal with the arguments like

./hello am i here

then try to modify it so that it tries to check if two strings are reverses of each other or not then you will need to check if argc parameter is exactly three if anything else print an error

if(argc!=3)/*3 because even the executables name string is on argc*/
{
    printf("unexpected number of arguments\n");
    return -1;
}

then check if argv[2] is the reverse of argv[1] and print the result

./hello asdf fdsa

should output

they are exact reverses of each other

the best example is a file copy program try it it's like cp

cp file1 file2

cp is the first argument (argv[0] not argv[1]) and mostly you should ignore the first argument unless you need to reference or something

if you made the cp program you understood the main args really...

Answer 3

For parsing command line arguments on posix systems, the standard is to use the getopt() family of library routines to handle command line arguments.

A good reference is the GNU getopt manual