Memory Allocation

Dart is a garbage-collected language. When you create Dart objects — such as strings or class instances — the Dart runtime is responsible for allocating memory and reclaiming it when those objects are no longer reachable.

This model does not extend across the FFI boundary.

When calling Win32 APIs through FFI, you are responsible for the lifetime of any native memory you allocate or receive from Windows. Understanding who owns a block of memory — and when it must be released — is essential for writing correct, leak-free interop code.

When Native Memory Is Required​

Only primitive values (such as integers) can be passed directly across the FFI boundary. All other data — such as strings, structs, and buffers — must reside in native memory.

As a result, FFI code typically follows this pattern:

• Allocate native memory explicitly
• Pass pointers to that memory into Win32 APIs
• Release the memory when it is no longer needed

Failing to release native memory will eventually exhaust the native heap and destabilize your application.

Allocating Native Memory​

Native memory is typically allocated using the calloc() allocator from package:ffi.

package:win32 additionally provides allocators such as adaptiveCalloc(), which behave like calloc() but also participate in optional leak tracking.

void main() {
  final pBuffer = adaptiveCalloc<Uint8>(256);
}

This allocates 256 bytes of zero-initialized memory and returns a Pointer<Uint8>. The memory can be accessed using indexed syntax:

for (var i = 0; i < 256; i++) {
  pBuffer[i] = i % 8;
}

Freeing Native Memory​

Allocated native memory must be released explicitly when it is no longer needed.

dart:ffi library exposes calloc.free(), but package:win32 provides a top-level convenience function free():

free(pBuffer);

Ownership Rules​

Every block of native memory has a single, well-defined owner.

If you allocate the memory, you must free it.

In practice:

Always consult the Windows API documentation to determine ownership of returned pointers and the correct way to release them.