'cannot convert from...' error during callback assignations (migrated code from C) - c

Question

I'm migrating some lines coded on C to C++/CLI (UI Windows Form based on .NET). One of my problems comes when I try to do this kind of assignation:
myCallbacks.cbf_data_write = this->dataWriteFunc;
In this case, dataWriteFunc is defined as:
PNIO_IOXS dataWriteFunc(PNIO_UINT32, PNIO_DEV_ADDR *, PNIO_UINT32, PNIO_UINT8 *, PNIO_IOXS);
And myCallbacks is declared as
PNIOD_CBF_FUNCTIONS myCallbacks;
with
typedef struct {
PNIO_UINT32 size; /* size of struct = sizeof(PNIO_CBF_FUNCTIONS) */
PNIO_CBF_DATA_WRITE cbf_data_write; /* mandatory */
PNIO_CBF_DATA_READ cbf_data_read; /* mandatory */
PNIOD_CBF_ASYNC_REC_READ cbf_async_rec_read; /* mandatory */
PNIOD_CBF_ASYNC_REC_WRITE cbf_async_rec_write; /* mandatory */
PNIOD_CBF_SYNC_ALARM_DONE cbf_sync_alarm_done; /* mandatory */
PNIOD_CBF_ASYNC_CONNECT_IND cbf_async_connect_ind; /* mandatory */
PNIOD_CBF_ASYNC_OWNERSHIP_IND cbf_async_ownership_ind; /* mandatory */
PNIOD_CBF_ASYNC_INDATA_IND cbf_async_indata_ind; /* mandatory */
PNIOD_CBF_SYNC_DISCONNECT_IND cbf_sync_disconnect_ind; /* mandatory */
PNIOD_CBF_SYNC_DATA_STATUS_IND cbf_sync_data_status_ind; /* mandatory */
PNIOD_CBF_ASYNC_PRM_END_IND cbf_async_prm_end_ind; /* mandatory */
PNIOD_CBF_SYNC_STOPPED cbf_sync_device_stopped; /* mandatory */
PNIOD_CBF_ASYNC_IRT_INIT_INPUTS cbf_async_irt_init_inputs; /* mandatory for IRT top */
PNIOD_CBF_SYNC_CP_STOP_REQ cbf_sync_cp_stop_req; /* optional */
PNIOD_CBF_SYNC_START_LED_FLASH cbf_sync_start_led_flash; /* optional */
PNIOD_CBF_SYNC_STOP_LED_FLASH cbf_sync_stop_led_flash; /* optional */
PNIOD_CBF_RESERVED
} ATTR_PACKED PNIOD_CBF_FUNCTIONS;
Also:
typedef PNIO_IOXS (*PNIO_CBF_DATA_WRITE) /* write data to IO stack (local ==> remote) */
(PNIO_UINT32 DevHndl, /* Handle for Multidevice */
PNIO_DEV_ADDR * pAddr, /* geographical address */
PNIO_UINT32 BufLen, /* length of the submodule input data */
PNIO_UINT8 * pBuffer, /* Ptr to data buffer to write to */
PNIO_IOXS Iocs); /* remote (io controller) consumer status */
So, what exactly I'm doing wrong? VS2012 gives me next error:
Error 4 error C2440: '=' : cannot convert from 'PNIO_IOXS (__thiscall CP1626::* )(PNIO_UINT32,PNIO_DEV_ADDR *,PNIO_UINT32,PNIO_UINT8 *,PNIO_IOXS)' to 'PNIO_CBF_DATA_WRITE' c:\users\hp\documents\visual studio 2012\projects\ui_cp1626\ui_cp1626\Profinet_IDevice.h 513 1 UI_CP1626
What's the correct form to associate callbacks in this case?
Thank you in advance.

Answer 1

You're trying to convert thiscall function (non-static class member function) to ordinary function. The problem is non-static class members take extra implicit argument, the pointer to class object aka this, so dataWriteFunc's implicit signature is:
PNIO_IOXS dataWriteFunc(CP1626 *this, PNIO_UINT32, PNIO_DEV_ADDR *,
PNIO_UINT32, PNIO_UINT8 *, PNIO_IOXS);
, note the 1st argument, it's implicit presence is what gives function "__thiscall" attribute. If you declare this function as
static PNIO_IOXS dataWriteFunc(PNIO_UINT32, PNIO_DEV_ADDR *,
PNIO_UINT32, PNIO_UINT8 *, PNIO_IOXS);
then the error will go away. Note that inside static methods this is not available.