First thing always is including Eina:

#include <stdio.h>
#include <Eina.h>

Next we initialize eina and create a string buffer to play with:

int main(int argc EINA_UNUSED, char **argv EINA_UNUSED)
{
   Eina_Strbuf *buf, *substr;

   eina_init();

   buf = eina_strbuf_new();

Here you can see two different ways of creating a buffer with the same contents. We could create them in simpler ways, but this gives us an opportunity to demonstrate several functions in action:

   eina_strbuf_append_length(buf, "BUFFE", 5);
   eina_strbuf_append_char(buf, 'R');
   printf("%s\n", eina_strbuf_string_get(buf));

   eina_strbuf_tolower(buf);
   printf("%s\n", eina_strbuf_string_get(buf));

   substr = eina_strbuf_substr_get(buf, 3, 2);
   printf("%s\n", eina_strbuf_string_get(substr));
   eina_strbuf_free(substr);

   eina_strbuf_insert_escaped(buf, "my ", 0);
   printf("%s\n", eina_strbuf_string_get(buf));
   eina_strbuf_reset(buf);

   eina_strbuf_append_escaped(buf, "my buffer");
   printf("%s\n", eina_strbuf_string_get(buf));
   eina_strbuf_reset(buf);

Next we use the printf family of functions to create a formatted string, add, remove and replace some content:

   eina_strbuf_append_printf(buf, "%s%c", "buffe", 'r');
   eina_strbuf_insert_printf(buf, " %s: %d", 6, "length", (int)eina_strbuf_length_get(buf));
   printf("%s\n", eina_strbuf_string_get(buf));

   eina_strbuf_remove(buf, 0, 7);
   printf("%s\n", eina_strbuf_string_get(buf));

   eina_strbuf_replace_all(buf, "length", "size");
   printf("%s\n", eina_strbuf_string_get(buf));

Once done we free our string buffer, shut down Eina and end the application:

   eina_strbuf_free(buf);

   buf = eina_strbuf_manage_read_only_new_length("Example string", 14);
   printf("%s\n", eina_strbuf_string_get(buf));

   eina_strbuf_append_char(buf, '.');
   printf("%s\n", eina_strbuf_string_get(buf));

   eina_strbuf_append_length(buf, "Another string.", 15);
   printf("%s\n", eina_strbuf_string_get(buf));

   eina_strbuf_free(buf);
   eina_shutdown();

   return 0;
}