Bubble sorting an array of strings in C - c

Question

I've been trying to bubble sort an array of strings but I always get the "Segmentation fault" Error.
Any help is appreciated.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
char *arreglo[20]={"Ruben","Modesta","Jan","Ana","Amparo","Josu","Azahara","Concepcio","Carmelo","Miguel","Francesc","Jairo","Jose","Luis","Teo","Jone","Jacobo","Ainoa","Natalia","Igor"};
int i;
int j;
char *temp;
for (int j=0; j<20; j++)
{
for (int i=j+1; i<20; i++)
{
if (strcmp(arreglo[j], arreglo[i]) > 0)
{
strcpy(temp, arreglo[j]);
strcpy(arreglo[j], arreglo[i]);
strcpy(arreglo[i], temp);
}
}
}
}

Answer 1

String literals are typically stored in read-only memory area, not intended to be modified.
In this question, there is no need to move the string literal. Instead, we can just modify the string pointers. It's faster and safer.
Please check this code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
const char *arreglo[20]={"Ruben","Modesta","Jan","Ana","Amparo","Josu","Azahara","Concepcio","Carmelo","Miguel","Francesc","Jairo","Jose","Luis","Teo","Jone","Jacobo","Ainoa","Natalia","Igor"};
int i;
int j;
const char *sorted[20];
for(i=0;i<20;i++){
sorted[i] = arreglo[i];
}
for (j=0; j<20; j++){
for (i=j+1; i<20; i++) {
if (strcmp(sorted[j], sorted[i]) > 0) {
const char *temp = sorted[j];
sorted[j] = sorted[i];
sorted[i] = temp;
}
}
}
for(i=0;i<20;i++){
printf("%d:%s\n",i,sorted[i]);
}
}
Pointers points to string literals are set to "const char *"
Hopefully this may help you solve your problem.

Answer 2

When you declare an array-of-pointers-to char and initialize each pointer to a string, each of those strings is a String Literal and cannot be modified (there are very few exceptions). In order to swap strings, each of the strings must reside in memory that can be modified -- like an array or within an allocated block of memory.
The simple solution in your case is to make arreglo a 2D array instead of an array-of-pointers, e.g. char arreglo[20][20]. You other option is to leave arreglo as an array-of-poiners, but then allocated storage for each pointer and then copy a name to each of the allocated blocks before sorting (a bit more involved).
You have the same issue with temp. You declare temp as a pointer, but it is not initialized to point to any valid storage before you attempt to use it in your swap routine. It too can simply be char temp[20]; for you data (though you only need declare it within the if statement)
Making those changes and tweaking the sort limits a bit, you could do:
#include <stdio.h>
#include <string.h>
int main (void) {
char arreglo[20][20] = {"Ruben", "Modesta", "Jan", "Ana", "Amparo", "Josu",
"Azahara", "Concepcio", "Carmelo", "Miguel", "Francesc",
"Jairo", "Jose", "Luis", "Teo", "Jone", "Jacobo",
"Ainoa", "Natalia", "Igor"};
for (int j = 0; j < 20 - 1; j++) {
for (int i = j + 1; i < 20; i++) {
if (strcmp(arreglo[j], arreglo[i]) > 0) {
char temp[20];
strcpy (temp, arreglo[j]);
strcpy (arreglo[j], arreglo[i]);
strcpy (arreglo[i], temp);
}
}
}
for (int i = 0; i < 20; i++)
puts (arreglo[i]);
}
(note: you do not need stdlib.h)
**Example Use/Output **
$ ./bin/bubblesort_2D_names
Ainoa
Amparo
Ana
Azahara
Carmelo
Concepcio
Francesc
Igor
Jacobo
Jairo
Jan
Jone
Jose
Josu
Luis
Miguel
Modesta
Natalia
Ruben
Teo
Look things over and let me know if you have questions.