return lstring_create(lemon, ptr, strlen(ptr));
If you are under Windows, then it the function will use ctime() which takes a single argument of type const time_t *.
As you can see buf is declared as char buf; but under Windows it's never used, therefore will throw a warning about unused variable.
In order to compile our code by letting our compiler know it's okay to have an unused variable, we cast buf to type void to silence possible warnings.
To make things clearer for you, try the following code:
int age = 100;
const char * name = "old man";
print("I'm a %d year old...thing!\n", age);