Question

Using the getopt function included in unistd.h in C++, is there a way to structure the optstring such that…

[-a] [-f "reg_expr"] out_file1 [[-f "reg_expr"] out_file2 ...] is possible?

This is a homework assignment, but the emphasis is not on this specific subtask.

In my head I would like to specify the following logic:

(a argument), (infinitely many f arguments with 2 required (sub)arguments),… (infinitely many generic arguments)

Perhaps my understanding of the getopt function is fundamentally flawed. I also saw a getopt_long. Perhaps that is what I’m missing.

I originally drafted this, which worked, but I came across the getopt function and thought it might do a better job.

int outFileFlags;
int outFileMode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
int i = 1;
while (i < argc){
    if (i == 1 && strcmp( argv[i], "-a") == 0){
        cout << "append flag set" << endl;
        outFileFlags = O_RDWR | O_APPEND;
        i++;
        continue;
    }
    else {
        outFileFlags = O_TRUNC | O_RDWR | O_CREAT;
    }
    if (strcmp( argv[i], "-f") == 0 && i+2 <= argc){
        cout << "   regx = " << argv[i+1] << endl;
        cout << "   fn = " << argv[i+2] << endl;
        i = i+3;
        continue;
    }
    else {
        cout << "   regx = none" << endl;
        cout << "   fn = " << argv[i] << endl;
        i++;
        continue;
    }
}

Note: assume this is written for a unix environment. I don’t think I can use anything from the standard library. I only included std::cout for testing purposes.

I will be happy to elaborate on any details of the assignment. However, the main question revolves around the syntax of the optstring. I am currently only aware of : meaning required and :: meaning optional is there a way to specify arguments that repeat like a regex wildcard *?

EDIT:

I’m sure this is sloppy due to the fact that I don’t think getopt is designed to handle multiple arguments per option but it does the trick…

int main(int argc, char *argv[]){
    char c;
    int iterations = 0;
    while (*argv) {
        optind = 1;
        if (iterations == 0){
            opterr = 0;
            c = getopt(argc, argv, "a");
            if(c == 'a'){
                //~ APPEND SET
            }
            else if(c=='?'){
                optind--;
            }
        }
        while ((c = getopt(argc, argv, "f:")) != -1) {
            if (c == 'f'){
                //~ REGEX = optarg
                if (optind < argc && strcmp(argv[optind], "-f") != 0) {
                    //~ FILENAME = argv[optind]
                    optind++;
                }
                else {
                    errno = 22;
                    perror("Error");
                    exit(errno);
                }
            }
            else {
                errno = 22;
                perror("Error");
                exit(errno);
            }
        }
        argc -= optind;
        argv += optind;
        iterations++;
        //~ REMAINING FILES = *argv
    }
}

Answer 1

You need to do a separate getopt loop for each group of options and output filename.

group_index = 0;
while (*argv) {
  optreset = 1;
  optind = 1;
  while ((ch = getopt(argc, argv, "af:")) != -1) {
    switch (ch) {
      /* process options */
    }
  }
  argc -= optind;
  argv += optind;
  outfile[group_index++] = *argv;
  argc--;
  argv++;
}