libssh2_free man page
libssh2_free — deallocate libssh2 memory
void libssh2_free(LIBSSH2_SESSION *session, void *ptr);
Deallocate memory allocated by earlier call to libssh2 functions. It uses the memory allocation callbacks provided by the application, if any. Otherwise, this will just call free().
This function is mostly useful under Windows when libssh2 is linked to one run-time library and the application to another.
Added in libssh2 1.2.8