C / C++ / MFC

10-Aug-04 22:24

I have been trying to define a structure and use it with a union, but the bit fields seem to cause the structure to be bigger than I expected.

e.g. ( 4 x 4 bit fileds + 2 float fields + short = 11 bytes)
But what I get is 28 bytes.

// Data1	w03_second_10_s_;<br />
typedef struct <br />
{<br />
	unsigned	 data 	:	4	;	<br />
}W03_SECOND_10_S_;<br />
<br />
// Data2	w03_second_1_s_;<br />
typedef struct <br />
{<br />
	unsigned	 data 	:	4	;	<br />
}W03_SECOND_1_S_;<br />
<br />
// Data3	w03_second_0_1_s_;<br />
typedef struct <br />
{<br />
	unsigned	 data 	:	4	;	<br />
}W03_SECOND_0_1_S_;<br />
<br />
// Data4	w03_second_0_01_s_;<br />
typedef struct <br />
{<br />
	unsigned	 data 	:	4	;	<br />
}W03_SECOND_0_01_S_;<br />
<br />
// Data5	w05_price;<br />
typedef struct <br />
{<br />
	float		data; <br />
}W05_PRICE;<br />
<br />
// Data6	w07_netCost;<br />
typedef struct <br />
{<br />
	float		data; <br />
}W07_NETCOST;<br />
<br />
// Data7	w08_index;<br />
typedef struct <br />
{<br />
	unsigned short		data; <br />
}W08_INDEX;<br />
// All the fields into a sigle structure<br />
typedef struct{<br />
W03_SECOND_10_S_	w03_second_10_s_;<br />
W03_SECOND_1_S_		w03_second_1_s_;<br />
W03_SECOND_0_1_S_	w03_second_0_1_s_;<br />
W03_SECOND_0_01_S_	w03_second_0_01_s_;<br />
W05_PRICE			w05_price;<br />
W07_NETCOST			w07_netCost;<br />
W08_INDEX			w08_index;<br />
}TEST1_10;

// Form a union between the message structure and a buffer<br />
union<br />
{<br />
	TEST1_10			message_data;		// I expect this to be = 14 bytes<br />
	unsigned short		buffer[32];			// Max buffer size<br />
}messageStructData;<br />
<br />
int sizeStruct = sizeof(messageStructData);

The size if 64 bytes, but the size of the TEST1_10 structure is 28 bytes (not 11 bytes)so each field of 4 bits is taking up 4 bytes

TEST1_10			message_data1;<br />
int sizeStruct1 = sizeof(message_data1);

sizeStruct1 = 28 bytes.

The short is being padded to 4 bytes as is each 4 bit field.

Is it possible to map bit fields onto a structure and then a union in C++.

Antony M Kancidrowski10-Aug-04 23:45

Antony M Kancidrowski

10-Aug-04 23:45

The best you will get is to set the byte alignment for structures to a single byte. Currently you must have it set to 4 bytes.

Look in the Project Settings under Code Generation

Ant.

I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Williams (Little Britain)

sweep12311-Aug-04 1:24

11-Aug-04 1:24

Thanks for your post, I set it to 1 byte and that reduced the count from 28 to 26.

Are they no way that I can used bit fields in the way I intended; i.e.

overlay these bit field and other fileds (short, float etc) with a buffer.

I did remove the wrapping of the bit fields from a struct:

typedef struct{<br />
	unsigned	 data1 	:	4	;	<br />
	unsigned	 data2 	:	4	;	<br />
	unsigned	 data3 	:	4	;	<br />
	unsigned	 data4 	:	4	;	<br />
	W05_PRICE			w05_price;<br />
	W07_NETCOST			w07_netCost;<br />
	W08_INDEX			w08_index;<br />
}TEST1_10;

this gave a size of 14 (2 floats, 1 short and 4 x 4 bit fields = 11 bytes)

But each 4 bit field is taking a byte; hence 14 bytes.

Any suggestions to get this scheme working?

Antony M Kancidrowski11-Aug-04 2:03

Antony M Kancidrowski

11-Aug-04 2:03

Without combining the fields in the struct I can not see how you can do this.

e.g.

typedef struct{<br />
BYTE data1and2; <br />
BYTE data3and4;<br />
W05_PRICE w05_price;<br />
W07_NETCOST w07_netCost;<br />
W08_INDEX w08_index;<br />
}TEST1_10;

Downside is that will have to do the bit manipulation on data1and2 and data3and4 in order to get the appropriate 4bit values however. Though a couple of functions should be enough to get and set the values.

Ant.

I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Williams (Little Britain)

David Crow11-Aug-04 5:25

David Crow

11-Aug-04 5:25

Contrast what you have with:

#pragma pack(1)
typedef struct
{
    unsigned data1 : 4; 
    unsigned data2 : 4;
    unsigned data3 : 4;
    unsigned data4 : 4;
    float data5;
    float data6;
    unsigned short data7;
} TEST1_10;
#pragma pack()

TEST1_10 message_data1;
int sizeStruct1 = sizeof(message_data1);

What is the value of sizeStruct1?

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

sweep12311-Aug-04 6:12

11-Aug-04 6:12

The size of the structure is 14 bytes.
I assume this is (8 for 2 floats + 2 for the short and 4 for the 4 bit fields)

I am after a size of 11 bytes.

Are they any settings that I have not made?

David Crow11-Aug-04 7:23

David Crow

11-Aug-04 7:23

You do know that sizeof() cannot be used on bit fields, don't you?

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

sweep12311-Aug-04 21:58

11-Aug-04 21:58

If I use the following code:-

typedef struct<br />
{ <br />
	unsigned short data1;<br />
//	unsigned data1 : 4;<br />
//	unsigned data2 : 4;<br />
//	unsigned data3 : 4;<br />
//	unsigned data4 : 4;<br />
	float data5;<br />
	float data6;<br />
	unsigned short data7;<br />
}TEST1_101;<br />
#pragma pack()<br />
TEST1_101 message_data1;<br />
int sizeStruct1 = sizeof(message_data1

);

I get size = 12 bytes, which I understand (8 for floats + 2 x 2 for shorts = 12 bytes. But why dont I get 12 for the following:-

typedef struct<br />
{ <br />
	unsigned data1 : 4;<br />
	unsigned data2 : 4;<br />
	unsigned data3 : 4;<br />
	unsigned data4 : 4;<br />
	float data5;<br />
	float data6;<br />
	unsigned short data7;<br />
}TEST1_101;<br />
#pragma pack()<br />
TEST1_101 message_data1;<br />
int sizeStruct1 = sizeof(message_data1);

David Crow12-Aug-04 2:58

David Crow

12-Aug-04 2:58

sweep123 wrote:
But why dont I get 12 for the following:-

I hinted at the fact that you cannot use sizeof() with bit fields. Did you miss that earlier?

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

sweep12312-Aug-04 4:17

Re: Dialog Keyboard Events

12-Aug-04 4:17

OK, yes I saw your post that stated that, but removed the bit fields and tried a few other things and then put back the bit fields.

I think the overlay works with the union, but the fact that a bug in my program and the sizeof() problem with bitfields led to confusion.

Thanks,

Dialog Keyboard Events

Joel Holdsworth10-Aug-04 22:14

Joel Holdsworth

10-Aug-04 22:14

Hi, I'm having a problem with a dialog. I need my dialog box to recieve/intercept all keyboard events that go on inside, but I'm getting problems where only the controls are reciving the keyboard events. Presumably only the window with the focus can ever recieve keyboard message. My dialog simply does not recieive any OnChar, OnKeyDown, or OnSysChar events. So I implemented OnKillFocus in the dialog like so...

void CMyDialog::OnKillFocus(CWnd* pNewWnd) 
{
	CWnd::OnKillFocus(pNewWnd);

	// The focus must be maintained so that we always recieve keyboard input
	SetFocus();
}

However this seems to make all my buttons totally unclickable! Does anyone have a solution to this at all?

Joel Holdsworth

Johan Rosengren11-Aug-04 6:44

Johan Rosengren

11-Aug-04 6:44

You might want to try overriding PreTranslateMessage for your dialog.

Visual C++ .net and Word 2003 automation

tiziacaia10-Aug-04 21:57

tiziacaia

10-Aug-04 21:57

I want write a doc file using Visual c++. I found a lot of microsoft examples but don't work.
Somebody has a project that work that i can use als examples?

Thanks a lot

Steve Thresher11-Aug-04 3:04

Steve Thresher

11-Aug-04 3:04

Try this Microsoft article[^]

Systems AXIS Ltd - Software for Business ...

tiziacaia11-Aug-04 4:12

tiziacaia

11-Aug-04 4:12

Thaks a lot but there aren't examples for office 2003.
My problem is that when i select the wrapped class, the file msword*.h and msword*.cpp aren't created but in the project i find only files for single classes that i selected (Capplication.h,CDocments.h,....)
Understand you my problem? Thanks a lot and i hope you understand my english Unsure | :~

Steve Thresher11-Aug-04 9:32

Steve Thresher

11-Aug-04 9:32

Can you give me more details on what you are attempting to do? Are you trying to use a framework such as MFC or just plain Win32 API? Are you trying to use the #import statement?

Systems AXIS Ltd - Software for Business ...

tiziacaia11-Aug-04 18:06

tiziacaia

11-Aug-04 18:06

I'm using MFC, and i tryed to use the #import but don't work.
I thing the biggest problem is my office version that is 2003. When i add the wrapped class (type library), there isn't file like msword*.h in my project but only a lot of new class for word (for example CApplication.h, CDocuments.h, CDocument0.h,......).
Undestand you my problem?
thanks