Like all examples we start by including Eina:

#include <stdio.h>

Here we declare some variables and initialize eina:

#include <Eina.h>

int
main(int argc EINA_UNUSED, char **argv EINA_UNUSED)
{
   const char *str, *str2;
   const char *prologe = "The Cylons were created by man. They rebelled. They "
                         "evolved.";
   const char *prologe2 = "%d Cylon models. %d are known. %d live in secret. "
                          "%d will be revealed.";
   const char *prologe3 = "There are many copies. And they have a plan.";

   eina_init();

We start the substantive part of the example by showing how to make a part of a string shared and how to get the length of a shared string:

   str = eina_stringshare_add_length(prologe, 31);
   printf("%s\n", str);
   printf("length: %d\n", eina_stringshare_strlen(str));

   eina_stringshare_del(str);

There are many ways of creating shared strings including an equivalent to sprintf:

   str = eina_stringshare_printf(prologe2, 12, 7, 4, 1);
   printf("%s\n", str);
   eina_stringshare_del(str);

An equivalent to snprintf:

   str = eina_stringshare_nprintf(45, "%s", prologe3);

But the simplest way of creating a shared string is through eina_stringshare_add():

   printf("%s\n", str);

Sometimes you already have a pointer to a shared string and want to use it, so to make sure the provider of the pointer won't free it while you're using it you can increase the shared string's ref count:

   str2 = eina_stringshare_add(prologe3);
   printf("%s\n", str2);

Whenever you have a pointer to a shared string and would like to change it's value you should use eina_stringshare_replace():

   eina_stringshare_ref(str2);
   eina_stringshare_del(str2);
   printf("%s\n", str2);

Warning:

Don't use eina_stringshare_del() followed by eina_share_common_add(), under some circumstances you might end up deleting a shared string some other piece of code is using.

We created str but haven't deleted it yet, and while we called eina_stringshare_del() on str2, we created it and then increased the ref count so it's still alive:

   eina_stringshare_replace(&str, prologe);
   printf("%s\n", str);

   eina_stringshare_del(str);
   eina_stringshare_del(str2);

You can see the full source code here.