warning C4020: 'function through pointer' : too many actual parameters

NTDEV
1

I declared a function pointer typedef like this:

typedef VOID
(*PXN_DEVICE_CALLBACK)(PVOID context, ULONG type, PVOID value);

And then defined it in a structure called xppdd and called it like this:

xppdd->device_callback(NULL, 1, NULL);

and got the following error for the function call:

warning C4020: ‘function through pointer’ : too many actual parameters

Which was (in the end) caused by me using the word ‘type’ as a parameter name. I checked and I can’t see where it is documented that ‘type’ is a reserved word for C, and if it was, I would have expected an error not a vague warning that didn’t give me any useful clues as to where the problem was.

I have changed type to callback_type and the problem has gone away, I’m just curious as to why it behaved that way as it was really frustrating for a few minutes.

Thanks

James

2

>

I declared a function pointer typedef like this:

typedef VOID
(*PXN_DEVICE_CALLBACK)(PVOID context, ULONG type, PVOID value);

And then defined it in a structure called xppdd and called it like this:

xppdd->device_callback(NULL, 1, NULL);

and got the following error for the function call:

warning C4020: ‘function through pointer’ : too many actual parameters

Which was (in the end) caused by me using the word ‘type’ as a parameter
name. I checked and I can’t see where it is documented that ‘type’ is a
reserved word for C, and if it was, I would have expected an error not a
vague warning that didn’t give me any useful clues as to where the problem
was.

I have changed type to callback_type and the problem has gone away, I’m
just curious as to why it behaved that way as it was really frustrating for a few
minutes.

In addition, one of my function declarations that gets assigned to xppdd->device_callback is declared like this:

static VOID
XenVbd_DeviceCallback(PVOID context, ULONG type, PVOID value) {
…
}

And that use of the word ‘type’ presents no problems at all.

Thanks

James

3

In my experience, this sort of thing is usually caused by an badly behaved preprocessor macro somewhere.

Try generating a preprocessed version (cl /EP) of the source file to see the source text that the compiler sees after the preprocessor. Usually, this makes the problem apparent if there was a poorly behaved macro involved.

  • S (Msft)

-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of James Harper
Sent: Friday, January 11, 2013 9:03 PM
To: Windows System Software Devs Interest List
Subject: RE:[ntdev] warning C4020: ‘function through pointer’ : too many actual parameters

I declared a function pointer typedef like this:

typedef VOID
(*PXN_DEVICE_CALLBACK)(PVOID context, ULONG type, PVOID value);

And then defined it in a structure called xppdd and called it like this:

xppdd->device_callback(NULL, 1, NULL);

and got the following error for the function call:

warning C4020: ‘function through pointer’ : too many actual parameters

Which was (in the end) caused by me using the word ‘type’ as a
parameter name. I checked and I can’t see where it is documented that
‘type’ is a reserved word for C, and if it was, I would have expected
an error not a vague warning that didn’t give me any useful clues as
to where the problem was.

I have changed type to callback_type and the problem has gone away,
I’m just curious as to why it behaved that way as it was really
frustrating for a few minutes.

In addition, one of my function declarations that gets assigned to xppdd->device_callback is declared like this:

static VOID
XenVbd_DeviceCallback(PVOID context, ULONG type, PVOID value) { …
}

And that use of the word ‘type’ presents no problems at all.

Thanks

James

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