Accessing extra field in CUcontext

I’m trying to save custom data in extra field of CUcontext, which has void* type using this code:

#include <cuda_runtime_api.h>
#include <cuda.h>
#include <iostream>

int main()
	CUcontext cu_ctx;
	cuCtxCreate(&cu_ctx, CU_CTX_SCHED_AUTO, 0);

	// Store a pointer to some extra data in the CUcontext.extra field
	int* my_extra_data = new int(42);
	cu_ctx->extra = my_extra_data;

	// Use the context and then destroy it
	// Do some CUDA operations...

	// Retrieve the extra data from the CUcontext.extra field and print it
	int* retrieved_extra_data = (int*)cu_ctx->extra;
	std::cout << "Extra data value: " << *retrieved_extra_data << std::endl;

	// Free the extra data memory
	delete retrieved_extra_data;

	return 0;

But I get the following error:

test.cpp:12:15: error: invalid use of incomplete type ‘struct CUctx_st’
   12 |         cu_ctx->extra = my_extra_data;
      |               ^~
In file included from test.cpp:2:
/usr/include/cuda.h:246:16: note: forward declaration of ‘struct CUctx_st’
  246 | typedef struct CUctx_st *CUcontext;                          /**< CUDA context */

Why I can’t access extra like that?