If it fails, we get NULL back but haven't free()d the old pointer; saving the NULL return over the old pointer forgets it, leaking the memory it pointed to. This is particularly severe in the JSON parser's grow(), where reading a very large JSON document can lead to the last successful realloc() in a doubling pattern being very large indeed; the subsequent failure will leak this very last allocation. Only worth checking for, however, when the subsequent code takes care to handle failure: in most cases, if realloc() fails, we're about to crash anyway. Change-Id: Icd3a503f169be224f0a058c58e8b7c82a3241ae7 Reviewed-by: Marc Mutz <marc.mutz@kdab.com> Reviewed-by: Anton Kudryavtsev <antkudr@mail.ru>