# How to deallocate userdata? **URL:** \ **Category:** FMOD Engine\ **Created:** [January 18, 2024, 9:51pm UTC](https://qa.fmod.com/t/how-to-deallocate-userdata/21120 "2024-01-18T21:51:12Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Speak4Erase](https://avatars.discourse-cdn.com/v4/letter/s/dc4da7/32.png) [@Speak4Erase](https://qa.fmod.com/u/Speak4Erase)\ **Post date:** [January 18, 2024, 9:51pm UTC](https://qa.fmod.com/t/how-to-deallocate-userdata/21120/1 "2024-01-18T21:51:12Z")
How do I deallocate any heap allocated userdata I set? ```cpp // bank used here as an example, but this could be anything Bank* bank; UserData* userData = new UserData; // how do I free this? bank->setUserData(userData); ``` All the examples I can find involve setting userdata to a value on the stack, nothing that uses `new` or `malloc`. ---
**Author:** ![aishi1](https://avatars.discourse-cdn.com/v4/letter/a/c57346/32.png) [@aishi1](https://qa.fmod.com/u/aishi1)\ **Post date:** [January 19, 2024, 10:57am UTC](https://qa.fmod.com/t/how-to-deallocate-userdata/21120/2 "2024-01-19T10:57:53Z")
Hello, if you don’t have access to `userData` when freeing, you could retrieve the pointer with `Bank::getUserData` and call `delete` on it after casting it back to `UserData *`. Something like this should work: ```cpp UserData *data; FMOD_RESULT result = bank->getUserData((void **)&data); if (result == FMOD_OK) { delete data; } else { // error } ``` ---
**Author:** ![Speak4Erase](https://avatars.discourse-cdn.com/v4/letter/s/dc4da7/32.png) [@Speak4Erase](https://qa.fmod.com/u/Speak4Erase)\ **Post date:** [January 19, 2024, 9:58pm UTC](https://qa.fmod.com/t/how-to-deallocate-userdata/21120/3 "2024-01-19T21:58:35Z")
How do I know when a bank (or any other object with associated userdata) is about to be released, so I can also deallocate the userdata associated with it? ---
**Author:** ![aishi1](https://avatars.discourse-cdn.com/v4/letter/a/c57346/32.png) [@aishi1](https://qa.fmod.com/u/aishi1)\ **Post date:** [January 20, 2024, 12:26am UTC](https://qa.fmod.com/t/how-to-deallocate-userdata/21120/4 "2024-01-20T00:26:49Z")
You could add a callback with [`FMOD::System::setCallback`](https://www.fmod.com/docs/2.00/api/studio-api-system.html#studio_system_setcallback) that checks for the callback type `FMOD_STUDIO_SYSTEM_CALLBACK_BANK_UNLOAD`. This callback passes the handle of the bank where you can get and deallocate the user data. Unless there’s a strong reason not to, I’d probably just make a class that wraps the bank + userdata and handles unloading/deallocating without needing callbacks. ---
**Author:** ![Speak4Erase](https://avatars.discourse-cdn.com/v4/letter/s/dc4da7/32.png) [@Speak4Erase](https://qa.fmod.com/u/Speak4Erase)\ **Post date:** [January 20, 2024, 12:31am UTC](https://qa.fmod.com/t/how-to-deallocate-userdata/21120/5 "2024-01-20T00:31:09Z")
Alright! I’ll try that, although I am a little worried about potential use after frees. ---
**Author:** ![Leah\_FMOD](https://yyz2.discourse-cdn.com/flex036/user_avatar/qa.fmod.com/leah_fmod/32/3685_2.png) [@Leah\_FMOD](https://qa.fmod.com/u/Leah_FMOD)\ **Post date:** [January 21, 2024, 9:39pm UTC](https://qa.fmod.com/t/how-to-deallocate-userdata/21120/6 "2024-01-21T21:39:32Z")
Besides what @aishi1 has already mentioned with regards to knowing when to release user data - to safely deallocate user data, set the user data to `nullptr` or equivalent with `setUserData()`, and then free your memory. User data isn’t touched by FMOD, except for when using [`FMOD_STUDIO_BANK_INFO`](https://www.fmod.com/docs/2.02/api/studio-api-system.html#fmod_studio_bank_info), where a non-zero `userdatalength` will cause FMOD to copy the data from your pointer to internal memory. ---
**Author:** ![Speak4Erase](https://avatars.discourse-cdn.com/v4/letter/s/dc4da7/32.png) [@Speak4Erase](https://qa.fmod.com/u/Speak4Erase)\ **Post date:** [February 1, 2024, 8:17pm UTC](https://qa.fmod.com/t/how-to-deallocate-userdata/21120/7 "2024-02-01T20:17:25Z")
So far I’ve gotten this strategy to (mostly) work, until I tried deallocating userdata attached to event descriptions. My code roughly looks like this: ```auto FMOD_RESULT deallocate_bank(Bank bank) { void* userdata; bank.get_userdata(&userdata); // deallocate the userdata if it is not null if userdata { delete (InternalBankUserdata*) userdata; bank.set_userdata(NULL); } std::vector list = get_event_list(bank); for (EventDescription event : list) { event.get_userdata(&userdata); // deallocate the userdata if it is not null if userdata { delete (InternalEventUserdata*) userdata; event.set_userdata(NULL); } } return FMOD_OK; } ``` `deallocate_bank` is called from a system callback, per aishi1’s solution. My `get_event_list` function uses `Bank::get_event_count` and `Bank::get_event_list` to get the list of all event descriptions. When I call either function though, they just return `FMOD_ERR_NOTREADY`. What should I do? ---
**Author:** ![Leah\_FMOD](https://yyz2.discourse-cdn.com/flex036/user_avatar/qa.fmod.com/leah_fmod/32/3685_2.png) [@Leah\_FMOD](https://qa.fmod.com/u/Leah_FMOD)\ **Post date:** [February 6, 2024, 10:25pm UTC](https://qa.fmod.com/t/how-to-deallocate-userdata/21120/8 "2024-02-06T22:25:18Z")
> [@Speak4Erase](#): > > My `get_event_list` function uses `Bank::get_event_count` and `Bank::get_event_list` to get the list of all event descriptions. When I call either function though, they just return `FMOD_ERR_NOTREADY`. What should I do? At the point where `FMOD_STUDIO_SYSTEM_CALLBACK_BANK_UNLOAD` fires, the bank has already been unloaded, and all resources freed. As a result, you won’t be able to iterate over the bank’s event descriptions from the callback - you’ll need to do that before unloading the bank.