Segmentation Fault while trying to copy string in C function - c

Question

I have a function in 'C' that is supposed to implement my own strcpy program. Here's what I wrote. However, I am not able to debug the cause of Segmentation Fault.
#include <stdio.h>
#include <stdlib.h>
char * mystrcpy(char *dest, char *src) {
char * ptr = dest;
while (*src != '\0'){
*ptr = *src;
ptr++; src++;
//printf("Dest is \"%s\" and Source is \"%s\"\n",dest,src);
}
*ptr = '\0';
return dest;
}
int main() {
char str[] = "I rock always";
char * dest = NULL;
dest = mystrcpy(dest, str);
printf("Source String %s and Destination String %s\n", str, dest);
}
Can someone explain this behavior to me ?

Answer 1

You have to allocate memory for the destination string:
int main() {
char str[] = "I rock always";
char * dest = (char*)malloc(strlen(str) + 1);
dest = mystrcpy(dest, str);
printf("Source String %s and Destination String %s\n", str, dest);
}
Of course, it is good manners to free the memory eventually:
free(dest);

Answer 2

You never allocate any memory for *dest to point to.
It starts pointing to NULL, and then you attempt: *ptr = *src.

Answer 3

#include <stdio.h>
/* this the K&R version of strcpy */
char * mystrcpy(char *dest, char *src) {
char *ptr = dest;
while ( *ptr++ = *src++ ) {;}
return dest;
}
int main(void) {
char str[] = "I rock always";
char dest[sizeof str];
char *result;
result = mystrcpy(dest, str);
printf("Source String %s and Destination String %s and result %s\n", str, dest, result);
return 0;
}

Answer 4

Allocate memory and try....
#include <stdio.h>
#include <stdlib.h>
char * mystrcpy(char *dest, char *src)
{
char * ptr = dest;
int index=0;
while (*src != '\0')
{
*(ptr+index) = *(src+index);
index++;
}
*(ptr+index) = '\0';
return dest;
}
int main()
{
char str[] = "I rock always";
char * dest = (char*)malloc((strlen(str)+1)*sizeof(char));
dest = mystrcpy(dest, str);
printf("Source String %s and Destination String %s\n", str, dest);
free(dest);
return 0;
}

Answer 5

You must allocate memory for the destination string buffer.
Memory management is a very big part of C ... you need to be very careful that you allocate AND deallocate memory as it is used and becomes surplus to requirements. Failure to do so will result in segmentation faults (failing to allocate memory) and memory leaks (failing to free memory)
Other answers here give you examples of malloc so I won't repeat them here.
You should use the functions already available to you as much as possible, rather than writing your own. This avoids errors in implementation as somebody has already debugged and optimized it for you.
http://www.cs.cf.ac.uk/Dave/C/node19.html