How to make strings stick together while radix sorting? - c

Question

I have to make a program that sort strings (with exact length 7 chars) by using radix sort. I already made a function that sort each column separately. My problem is how to make the whole string move, not just one char. It's really problematic for me to see how should it work in C.
I made one array "char strings[3][8]" and "char output[3][8]" to get sorted 3 strings with exact 7 chars in each one. For example sorting these strings:
strcpy(strings[0], "kupbars");
strcpy(strings[1], "daparba");
strcpy(strings[2], "jykaxaw");
In output I get:
dakaaaa
juparbs
kypbxrw
Each column is sorted correctly but chars don't stick together. I tried many ways for 3 hours but nothing works.
My code looks like this:
void countingSort(char a[][8], char b[][8]) {
int c[123];
for (int pos = 6; pos >= 0; pos--) {
for (int i = 0; i < 123; i++)
c[i] = 0;
for (int i = 0; i < 3; i++)
c[(int)a[i][pos]]++;
for (int i = 1; i < 123; i++)
c[i] += c[i - 1];
for (int i = 2; i >= 0; i--) {
b[--c[(int)a[i][pos]]][pos] = a[i][pos];
}
}
}
(There are constants limiting string length etc. because it's easy to change it to variable - I just focused on getting this program work properly.)

Answer 1

Try changing the loop to move an entire string:
for (int i = 2; i >= 0; i--) {
int k = --c[(int)a[i][pos]];
for(int j = 0; j < 8; j++) {
b[k][j] = a[i][j];
}
}

Answer 2

You could do a circular list but it's a little overhead. I propose you to use memmove().
#include <string.h>
void array_move_forward(char array[3][8]) {
for (int i = 0; i < 3; i++) {
char tmp = array[i][6];
memmove(array[i] + 1, array[i], 6);
array[i][0] = tmp;
}
}
void array_move_rewind(char array[3][8]) {
for (int i = 0; i < 3; i++) {
char tmp = array[i][0];
memmove(array[i], array[i] + 1, 6);
array[i][6] = tmp;
}
}
A other solution would be to manipulate your string yourself and using a index, that indicate the first letter of your string.
{
char str[7];
int i = 0;
...
int j = i;
for (int k = 0; k < 7; k++) {
char tmp = str[j++ % 7];
}
}
With that you could rotate your string just with i++ or i--.
struct my_string_radix {
char str[7];
int begin;
}