C - Function with variable number of arguments and command line arguments

Question

I need to sort n number of strings lexicographically that are arguments of a function with variable number of arguments. In main function, strings are read as command line arguments.

Here is my code:

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

void sort(int n,...)
{
    //store optional arguments (strings) to array arr
    va_list args;
    va_start(args,n);
    char **arr=malloc(n * sizeof(char*));
    int i;
    for(i=0;i<n;i++)
        arr[i]=malloc((strlen(va_arg(args,char*)) + 1) * sizeof(char));
    va_end(args);

    //store length of each string to lenArr
    //find max length and store it to temp (for sorting)
    va_list args;
    va_start(args,n);
    int *lenArr=calloc(n , sizeof(int));
    for(i=0;i<n;i++)
    {
        lenArr[i]=strlen(va_arg(args,char*)) + 1;
    }

    int max=0;
    for(i=0;i<n;i++)
    {
        if(lenArr[i] > lenArr[max])
            max=i;
    }
    int maxLen;
    maxLen=lenArr[max];
    char *temp=calloc(maxLen * sizeof(char));
    va_end(args);

    //sort array arr lexicographically 
    int j,min;
    for(i=0;i<n-1;i++)
    {
        for(min=i,j=i+1;j<n;j++)
           if(strcmp(arr[j],arr[min]) < 0)
                min=j;
           if(min!=i)
           {
              strcpy(temp,arr[i]);
              strcpy(arr[i],arr[j]);
              strcpy(arr[j],temp); 
           }
    }
}

int main(int argc,char **argv)
{
    int n=3;
    sort(n,argv[1],argv[2],argv[3]);//this works when n is pre-defined


    return 0;
}

How to read n strings as command line arguments in main function and print them sorted?

Also, I am am getting an error in function sort() - redeclaration of args with no linkage.

You can't do it — well, not without extortionate pain and a special library. Pass the array from the command line to a modified sort function that takes an array. The original code can then use this other function to do the sorting of the array it creates from a variable argument list. The basic problem is that you can't build up a variable number of arguments in a function call argument list at run-time. (But it isn't really clear what your sort function is up to. It sorts some data, but does nothing with the sorted data.) — Jonathan Leffler
– Jonathan Leffler, Commented Sep 20, 2016 at 21:26
Just pass the argument array in knowing you don't want the first one; easy. — ChiefTwoPencils
– ChiefTwoPencils, Commented Sep 20, 2016 at 21:27
I'm suggesting that it is rather difficult to simulate the effect of sort(3,argv[1],argv[2],argv[3]); and sort(4,argv[1],argv[2],argv[3],argv[4]); without writing the alternatives out like that. OTOH, it is trivial to call sort_alternative(argc-1, argv+1); — as shown in the answer I see at the moment. — Jonathan Leffler
– Jonathan Leffler, Commented Sep 20, 2016 at 21:51

BLUEPIXY · Accepted Answer · 2016-09-20 21:39:49Z

2

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

int cmp(const void *a, const void *b){
    return strcasecmp(*(char**)a, *(char**)b);
}

void sort(int n, char *str[n]){
    qsort(str, n, sizeof(char*), cmp);
}

int main(int argc, char *argv[]){
    sort(argc-1, argv+1);
    for(int i = 1; i < argc; ++i)
        puts(argv[i]);
    return 0;
}

Execution example:

>a.out a B c Z x y
a
B
c
x
y
Z

edited Sep 20, 2016 at 21:39

answered Sep 20, 2016 at 21:32

BLUEPIXY

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3 Comments

AdminXVII Over a year ago

Would be better with a bit of explanation

ufo Over a year ago

@BLUEPIXY, You didn't use variable number of arguments.

BLUEPIXY Over a year ago

@ufo It is not required if you use the argc and argv as command line arguments. (Also Even if there is a function with a variable argument, it is impossible to pass a variable parameters at runtime.)

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