# BNNSGraphContextSetOutputAllocationCallback(_:_:_:_:_:) Sets the allocation and deallocation callbacks for function outputs. ``` func BNNSGraphContextSetOutputAllocationCallback(_ context: bnns_graph_context_t, _ realloc: bnns_graph_realloc_fn_t?, _ free: bnns_graph_free_all_fn_t?, _ user_memory_context_size: Int, _ user_memory_context: UnsafeMutableRawPointer?) -> Int32 ``` ## Parameters `context` The graph context. `realloc` The memory allocation and reallocation function. If you pass `nil` for this parameter, you must also set `nil` for the `free` parameter. In this case, graph execution uses the default BNNS allocation mechanism. `free` The memory allocation and reallocation function. If you pass `nil` for this parameter, you must also set `nil` for the `realloc` parameter. In this case, graph execution uses the default BNNS allocation mechanism. `user_memory_context_size` The size, in bytes, `user_memory_context`. `user_memory_context` A pointer that that BNNS passes unmodified in all calls to `realloc` and `free`. ## Return Value `0` on success, nonzero on failure. ## Discussion If BNNS can’t bound the required output size prior to execution — for example, if the tensor sizes depend on input data — it allocates outputs during execution. Use this function to override the default memory allocation mechanisms. If you pass the same `user_memory_context` to [`BNNSGraphContextSetWorkspaceAllocationCallback(_:_:_:_:_:)`](/documentation/Accelerate/BNNSGraphContextSetWorkspaceAllocationCallback(_:_:_:_:_:)) and [`BNNSGraphContextSetOutputAllocationCallback(_:_:_:_:_:)`](/documentation/Accelerate/BNNSGraphContextSetOutputAllocationCallback(_:_:_:_:_:)), BNNS only calls the `free` function once. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)