Iterating through options of ls program from the command line

Question

I am writing a program that is a custom version of ls with some options. The options can be inputted as "-i" or as something like "-ilR". This portion of my code iterates through the command line arguments and sets a struct accordingly. Except if I run the program with "./myProgram -i Directory" it doesn't go into the test print I have set up.

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <sys/fcntl.h>
#include <stdbool.h>
#include <string.h>

struct optionArguments{
    bool argumenti;
    bool argumentl;
    bool argumentR; 
};

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

    struct optionArguments options;
        options.argumenti = false;
        options.argumentl = false;
        options.argumentR = false;

   
    for(int i = 1; i<argc-2; i++){
        for(int j = 0; j<strlen(argv[i]); j++){
            char chr = argv[i][j];
            if(chr == 'i'){
                options.argumenti = true;
            }
            if(chr == "l"){
                options.argumentl = true;
            }
             if(chr == "R"){
                options.argumentR = true;
            }
        }
    }

    if(options.argumenti){
        printf("OPTION I\n");
    }
}

any help/advice is greatly appreciated

edit: I just put a test print inside of the second loop and it doesn't print anything at all so the second loop isn't even running.

Have you tried debugging (or even using prints) to see what values you are looking at and which bits of the code are being executed? — John3136, Aug 05 '20 at 23:35
@WilliamPursell because argv[argc] will be a null pointer and argv[argc-1] is the directory argument — Steve, Aug 05 '20 at 23:36
You can't use `==` to compare strings in C, or a char to a string. — Shawn, Aug 05 '20 at 23:51
@John3136 I just put a test print inside of the second loop and it doesn't print anything at all so the second loop isn't even running. Do you have any idea why? — Steve, Aug 05 '20 at 23:52
@Shawn You can compare characters to characters with `==`, though, and it looks like that's what the OP was trying to do. The double-quotes instead of single-quotes look like a typo, since they use single quotes the first time around. — Charles Srstka, Aug 05 '20 at 23:58
@DayneHack Well, what arguments are you invoking your program with on the command line? Since you're going from `1` to ` — Charles Srstka, Aug 06 '20 at 00:03
@DayneHack try changing the `argc-2` to `argc-1` for `./myProgram -i Directory` arguments. — Sourabh Choure, Aug 06 '20 at 00:08
Try printing argc - maybe that isn't what you expect (3 args, argc -2, 1<1)... — John3136, Aug 06 '20 at 00:26

Sourabh Choure · Answer 1 · 2020-08-06T01:22:37.810

It will be much simpler if you use getopt() function designed to handle command-line argument parsing.

Note: Since you have already included unistd library so using getopt which will be much wiser, otherwise, there are other implementations available as well like argp()

Here is a program which uses getopt from the POSIX C Library unistd

#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <dirent.h>
#include <sys/fcntl.h>
#include <stdbool.h>
#include <string.h>

struct optionArguments{
    bool argumenti;
    bool argumentl;
    bool argumentR; 
};

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

    struct optionArguments options;
        options.argumenti = false;
        options.argumentl = false;
        options.argumentR = false;

    int opt;
    while ((opt = getopt(argc, argv, "ilR")) != -1) {
        switch (opt) {
        case 'i': options.argumenti = true; break;
        case 'l': options.argumentl = true; break;
        case 'R': options.argumentR = true; break;
        default:
            fprintf(stderr, "Usage: %s [-ilR] \n", argv[0]);
            exit(EXIT_FAILURE);
        }
    }


    if(options.argumenti){
        printf("OPTION I\n");
    }
    if(options.argumentl){
        printf("OPTION l\n");
    }
    if(options.argumentR){
        printf("OPTION R\n");
    }
}

For other ways of implementation visit: Parsing command-line arguments in C?

Iterating through options of ls program from the command line

1 Answers1