Taking arguments as input from terminal

Question

this is part of a function that takes input from terminal and sorts them depending on what the inputs are (sorting type, a version/variation of the sorting method to use, and the size of the array). This is what I have so far:

int main(int argc, char * argv[]) { //will have 3 arguments not including function name: sortingtype, version and arr size
    int * arr = make_arr(argv[2], argv[3]); //[2]

    if (strcmp(argv[1], "sortingtype1") == 0) {
        SortingType1(arr, argv[3]); //[2][3]
    }
    else if (strcmp(argv[1], "sortingtype2") == 0) {
        SortingType2(arr, argv[3]); //[2][3]
    }
    else {
        return 0;
    }
}

void test(){ //[1]
    main("sortingtype1", "a", 10); //sortingtype, version and arr size
}

[1] I have a function test() to simulate input from terminal but I don't know if it works that way. I get an error saying that there are too many arguments to main.

[2] Whether or not I remove that testing function, I still get warnings about "passing argument (the arguments with argv[X]) makes integer from pointer without a cast".

[3] These also need to be type int and not type char*, how do I change them?

Any suggestions on how to go about this? I have seen solutions using sscanf, but would prefer a more basic solution around my skill level first for understanding.

Edit: segmentation faults from

int * SortingType2(int * arr, int len) {
    for (int i=1; i < len; i++) {
        int x = arr[i];
        int j = i;
        while ((j > 0) && (x < arr[j-1])) {
            arr[j] = arr[j-1];
            j--;
        }
        arr[j] = x;
    }
    return arr;
}

int main(int argc, char * argv[]) {
    int size;
    if (argc > 3) size = atoi(argv[3]);

    int * arr = make_arr(argv[2][0], size);

    if (strcmp(argv[1], "sortingtype1") == 0) {
        SortingType1(arr, size);
    }
    else if (strcmp(argv[1], "sortingtype2") == 0) {
        SortingType2(arr, size);
    }
    else {
        return 0;
    }
}

Answer 1

If you want to call main() from a function, then you have to pass an argument count and a pointer to an array of strings that is null terminated (see What should main() return in C and C++? for the details).

Thus, you might write:

void test(void)
{
    char *argv[] = { "sortingtype", "a", "10", 0 };
    main(3, argv);
}

It is not common to do this. There is no evidence in your code of the test() function being called.

Note that the arguments are not modifiable strings in the code shown above; normally, the arguments are modifiable. If that's going to matter, you have to work a bit harder:

void test(void)
{
    char arg0[] = "sortingtype";
    char arg1[] = "a";
    char arg2[] = "10";
    char *argv[] = { arg0, arg1, arg2, 0 };
    main(3, argv);
}

Note too that all the arguments in argv should be strings. Your original code seemed to try to pass 10 rather than "10" but that is not allowed in the argument vector (though 10 could be valid as the argument count, of course).

---

Please note that calling main() recursively is an eccentric thing to do at best. It is seldom actually necessary, or desirable. It is, however, legal in C — but it is not legal in C++.

Answer 2

argv[] is an array of strings, so you need to convert them if you want integers. The simplest way to do this is with atoi() or sscanf(). atoi() is in stdlib.h, and sscanf() is in stdio.h. With atoi(), you just give it a string, and it returns an int. With sscanf(), you provide a string, conversion specifiers, and addresses of variables, just as in the scanf() function, the difference being that here you are scanning a string instead of stdin. Here is an example:

#include <stdio.h>   // needed for atoi()
#include <stdlib.h>  // needed for sscanf()

int main(int argc, char *argv[])
{
    int i = 0;
    int j = 0;

    /* if argv[1] exists, convert to int */
    if (argc > 1)
        i = atoi(argv[1]);

    /* if argv[2] exists, convert to int */
    if (argc > 2)
        sscanf(argv[2], "%d", &j);

    printf("%d -- %d\n", i, j);

    return 0;
}

If you compile this code and execute it you get, for example:

david scratch λ> ./a.out 123 456
123 -- 456

Working with your code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

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

    if (argc < 4) {
        printf("Usage: %s sortingType state size\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    size = atoi(argv[3]);

    int * arr = make_arr(argv[2], size);

    if (strcmp(argv[1], "sortingtype1") == 0) {
        SortingType1(arr, size);
    }
    else if (strcmp(argv[1], "sortingtype2") == 0) {
        SortingType2(arr, size);
    }

    return 0;
}