Sorting command line arguments in C

Question

I need to create a program that sorts command line strings. (Example output under code) This is the code I have so far:

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

int stringcomp (const void * x, const void * y);   

int main(int argc, char *argv[]){  
int i,j;
int k = 1;
char strings[argc-1][20]; 

strcpy(strings[0], argv[1]);
for(i=2; i< argc-1; i++){       
  strcat(strings[k],argv[i]);
  k++;
}
qsort(strings, argc, 20, stringcomp);
for(j=0 ; j < argc-1; j++){  
    printf("%s ", strings[j]);  
}  
return 0;  
}

int stringcomp (const void *x, const void *y) {  
return (*(char*)x -*(char*)y);  
}  

This is what I type into the command line: ./inOrder hello darkness my old friend

This is what I should get: darkness friend hello my old

But this is what I keep getting: ?darkness ?old ]@my

What am I doing wrong?

Answer 1

I hope this helps. There is no need to use strcat. Also I removed some of your variables.

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

#define MAX_STRING 20 /* maximum string length */

int stringcomp (const void * x, const void * y);   

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

    int i;
    int argCount = argc-1;
    char strings[argCount][MAX_STRING]; 


    /* copy from argv */
    for (i = 0; i < argCount; i++){
        strcpy( strings[i], argv[i + 1]);
    }

    /* sort the words*/
    qsort (strings, argCount, MAX_STRING, stringcomp);

    /* print the results */
    printf("\n");
    for (i = 0; i < argCount; i++){
        printf("%s\n", strings[i]);
    }

    return 0;  
}


int stringcomp (const void *x, const void *y) {  
    return (*(char*)x -*(char*)y);  
}  

Hope this helps :)

Answer 2

Continuing from the comments, in order to compare the strings and sort an array of strings, you have 2-levels of indirection to deal with. So your stringcomp function will need to look something like:

int stringcomp (const void *x, const void *y) {  
    return strcmp (*(char * const *)x, *(char * const *)y);  
}

Beyond that, instead of copying strings, why not just sort an array of pointers to sort the arguments in correct order? Something like the following is all you need:

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

int stringcomp (const void * x, const void * y);   

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

    char *strings[argc-1];  /* declare an array of pointers */
    int i;

    /* assign each argument to a pointer */
    for (i = 1; i < argc; i++)
        strings[i-1] = argv[i];

    /* sort the array of pointers alphabetically with qsort */
    qsort (strings, argc - 1, sizeof *strings, stringcomp);

    /* output the results */
    for (i = 0; i < argc-1; i++)
        printf("%s ", strings[i]);  

    putchar ('\n');

    return 0;  
}

int stringcomp (const void *x, const void *y) {  
    return strcmp (*(char * const *)x, *(char * const *)y);  
}

Example Use/Output

$ ./bin/sort_argv my dog has fleas
dog fleas has my

Look it over and let me know if you have additional questions.