Pointers and String manipulation

Question

I'm writing a function/method in C that is supposed to do the following:

/** * Recieves the list of arguments and copies to conffile the name of * the configuration file. * Returns 1 if the default file name was used or 2 if * the parameter -f existed and therefor the specified name was used. Returns 0 if there is a -f * parameter but is invalid. (last argument)
*/

Basically one of these two option will be "asked" by the program:

1- controller -f FCFS|LOOK

2- controller FCFS|LOOK

If the second is asked, we enter the case of using the default name.

 int get_conf_name(char* argv[], char* conffile) { 

// Searches for -f 

 s = strstr(*argv, "-f");


if(s != NULL){

      if(//its valid){
 strcpy(conffile, //the name of the file which comes after -f

 return 2

 }

      else return 0

 }

 else{

 strcpy(confile, "config.vss")

 return 1

 }

 }

The problem here is how do I get the word after -f and copy it to confile? And, can I access argv the same way I access conffile, since one of them is an array? I thought of using a for loop and a strlen, but that would be a lot of unecessary work for the computer wouldn't it?

That's not how strstr works. strstr looks for a substring (needle) in another string (haystack). What you want instead is looking for a whole string in an array of strings. You should use a loop. — Giulio Franco
– Giulio Franco, Commented Oct 27, 2013 at 16:48
btw: options are "passed to" (not "asked by") the program. Unless you're referring to the caller program. — Giulio Franco
– Giulio Franco, Commented Oct 27, 2013 at 16:51
@Giulio Franco Oh thanks :D By asked I meant there's two possible options for the user to ask the program — BVCGAAV
– BVCGAAV, Commented Oct 27, 2013 at 17:06

Sergey Kalinichenko · Accepted Answer · 2013-10-27 16:48:47Z

3

I think the assignment expects you to go through the individual arguments one by one, comparing them to "-f".

If you see no -f, you know that the default file needs to be used
If you see the flag in the final position, you know that the -f is invalid
If you see the flag in the position k, then the file name will be in argv[k+1]

The skeleton of your program should look like this:

bool foundFlag = false;
for (int i = 1 ; i < argc ; i++) {
    if (strcmp(argv[i], "-f") == 0) {
        if (i == argc-1) {
            // Error
        } else {
            // argv[i+1] is the file name;
        }
        foundFlag = true;
        break;
    }
}
if (!foundFlag) {
    // Default name is used
}

answered Oct 27, 2013 at 16:48

Sergey Kalinichenko

729k85 gold badges1.2k silver badges1.6k bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

BVCGAAV Over a year ago

Thank you, the skeleton is very clean and understandable :D So now, I can use argv[i+1] directly on strcpy right? But won't that [i+1] point to the space instead of the first char of the name?

Sergey Kalinichenko Over a year ago

@ipg24 That's the thing - spaces and tabs are taken out of the original command string when it is tokenized. Only non-whitespace characters are kept.

BVCGAAV Over a year ago

Understood :) Thanks a lot, now I know how to structure and write the whole thing!

Collectives™ on Stack Overflow

Pointers and String manipulation

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related