Comment by Marat_Dukhan

This is neat, but please add a pointer to deallocation function to sds header and use it in sdsfree. This will allow to return sds strings from functions in shared libraries. A common problem it that the user of the library might use a different version of libc than the shared library (this is especially typical on Windows), and when it calls sdsfree on an sds string allocated with a different libc, something awful will happen (in the best case, it will just leak memory). By storing a pointer to the deallocation function in the code which allocated the string you can make sure that it is always released by the same libc version that allocated it.