Question

I found this function and I don’t understand certain parts of it. I have about 3 days worth of C experience, so bear with me. This function serves a purpose of parsing command-line arguments.

1. Why do they reassign *arg to *c ?

2. I don’t understand why they are running a while loop.

3. Secondly, why would they run a while loop against a char pointer? I understand that a char is actually an array of characters, but my understanding is that they would only run a while loop against a char is to access the array character values individually, and they don’t do any of that.

4. How can you increment against a char?

5. Why do we even have *c?

6. I added the string check to see if the arg is -styles for example, which has a - so I can parse the flag and obtain the value, which is the next arg in argv — is that correctly used?

Like I said, I’ve got about 3 days of C experience, so please be thorough and methodical and as helpful as possible as to help me better understand this function and C overall.

void print_args(int argc,char *argv[])
{
     int i;
     if(argc > 1){
       for(i=1;i<argc;i++){
           char *arg = argv[i];
           char *c = arg;
           while(*c){
             if(strchr("-", *c)){
                 printf("arg %d: %s -> %s\n",i,arg,argv[i+1]);
             }  
             c++;
         }
       }
     }
 }

Answer 1

1) arg is assigned to point to the head of the current char array, and c is used to traverse the array.

2,3,5) The while loop is run until c points to (char)0, which incidently is also \0. So in effect they go over every character in the char array, until they reach the null terminator symbol. A better conditional would have been while (*c != '\0'), rather than relying implicitly that '\0' == 0

4) They increment a pointer, Thus having it point to the next memory cell, i.e. the next array cell.

6) Your addition will work as a test to recognise an option, you’d still have to compare it against -styles to see that it is indeed a valid option.

This code sample could do with a lot of fixing up to make it more robust and clearer.
If this is from a book or C tutorial, I suggest you look for another.