Sending data packets

I have a class and functions for making a "packet" to send. Basically it's just code to be decoded on the other side. I use HIBYTE and LOBYTE to change characters to numbers, but I don't think it works. Is there anything wrong with the code?

Code:

class CPaintTool
{
public:
	BYTE ToolID;	//All use

	CWCOORD pStart;	//All use
	CWCOORD pEnd;		//Rectangle and Line only

	WORD LineWidth;	//All use

	WORD Radius;	//Circles only

	BYTE cRed;		//All use
	BYTE cGreen;	//All use
	BYTE cBlue;		//All use

	char szPacket[20];

	void MakePacket();
	void BreakPacket();
};

void CPaintTool::MakePacket()
{
	ZeroMemory(&szPacket, 20);
	wsprintf(
		szPacket,
		"%c%c%c%c%c%c%c%c%c%c%c%c%c%c\r\n",
		ToolID,
		HIBYTE(pStart.x),
		LOBYTE(pStart.x),
		HIBYTE(pStart.y),
		LOBYTE(pStart.y),
		HIBYTE(pEnd.x),
		LOBYTE(pEnd.x),
		HIBYTE(pEnd.y),
		LOBYTE(pEnd.y),
		HIBYTE(LineWidth),
		LOBYTE(LineWidth),
		cRed,
		cGreen,
		cBlue
		);
}

void CPaintTool::BreakPacket()
{
	ToolID = (BYTE)szPacket[0];
	pStart.x = MAKEWORD((BYTE)szPacket[2], (BYTE)szPacket[1]);
	pStart.y = MAKEWORD((BYTE)szPacket[4], (BYTE)szPacket[3]);
	pEnd.x = MAKEWORD((BYTE)szPacket[6], (BYTE)szPacket[5]);
	pEnd.y = MAKEWORD((BYTE)szPacket[8], (BYTE)szPacket[7]);
	LineWidth = MAKEWORD((BYTE)szPacket[10], (BYTE)szPacket[9]);
	cRed = (BYTE)szPacket[11];
	cGreen = (BYTE)szPacket[12];
	cBlue = (BYTE)szPacket[13];	
}

Using sprintf() to "format" binary data which may well contain \0 characters is a bad move.

Just do
szPacket[1] = HIBYTE(pStart.x);
etc

When I breakpoint after making the packet, it says that it's a bad pointer, and each character in szPacket is bad. I don't get it

Code:

class CWCOORD
{
public:
	WORD x;
	WORD y;
};

class CPaintTool
{
public:
	BYTE ToolID;	//All use

	CWCOORD pStart;	//All use
	CWCOORD pEnd;		//Rectangle and Line only

	WORD LineWidth;	//All use

	WORD Radius;	//Circles only

	BYTE cRed;		//All use
	BYTE cGreen;	//All use
	BYTE cBlue;		//All use

	char szPacket[20];

	void MakePacket();
	void BreakPacket();
	CPaintTool();
};

CPaintTool::CPaintTool()
{
	ToolID = 0;
	pStart.x = 0;
	pStart.y = 0;
	pEnd.x = 0;
	pEnd.y = 0;
	LineWidth = 0;
	Radius = 0;
	cRed = 0;
	cGreen = 0;
	cBlue = 0;
	ZeroMemory(szPacket, 20);
}

void CPaintTool::MakePacket()
{
	ZeroMemory(szPacket, 20);
	szPacket[0] = ToolID;
	szPacket[1] = HIBYTE(pStart.x);
	szPacket[2] = LOBYTE(pStart.x);
	szPacket[3] = HIBYTE(pStart.y);
	szPacket[4] = LOBYTE(pStart.y);
	szPacket[5] = HIBYTE(pEnd.x);
	szPacket[6] = LOBYTE(pEnd.x);
	szPacket[7] = HIBYTE(pEnd.y);
	szPacket[8] = LOBYTE(pEnd.y);
	szPacket[9] = HIBYTE(LineWidth);
	szPacket[10] = LOBYTE(LineWidth);
	szPacket[11] = HIBYTE(Radius);
	szPacket[12] = HIBYTE(Radius);
	szPacket[13] = cRed;
	szPacket[14] = cGreen;
	szPacket[15] = cBlue;
	szPacket[16] = '\r';
	szPacket[17] = '\n';
	szPacket[18] = '\0';
}

void CPaintTool::BreakPacket()
{
	ToolID = (BYTE)szPacket[0];
	pStart.x = MAKEWORD((BYTE)szPacket[2], (BYTE)szPacket[1]);
	pStart.y = MAKEWORD((BYTE)szPacket[4], (BYTE)szPacket[3]);
	pEnd.x = MAKEWORD((BYTE)szPacket[6], (BYTE)szPacket[5]);
	pEnd.y = MAKEWORD((BYTE)szPacket[8], (BYTE)szPacket[7]);
	LineWidth = MAKEWORD((BYTE)szPacket[10], (BYTE)szPacket[9]);
	Radius = MAKEWORD((BYTE)szPacket[12], (BYTE)szPacket[11]);
	cRed = (BYTE)szPacket[13];
	cGreen = (BYTE)szPacket[14];
	cBlue = (BYTE)szPacket[15];	
}

I take it you noticed this in the original code.
ZeroMemory(&szPacket, 20);

> it says that it's a bad pointer, and each character in szPacket is bad.
How can an array be a bad pointer,. unless you've failed to construct the class which surrounds it.

And what do you mean each character is bad?
For sure it isn't going to be a printable string, so there's no use trying to print it to the screen (the \r\n\0 at the end are redundant)

In order to make sense of szPacket in the debugger, you need to display it in hex mode, not ascii mode.

isn't that what I'm doing with the HIBYTE/LOBYTE crap? How would I save it in hex? All that happens is I MakePacket(), send it to the other computer, BreakPacket, and then DrawObj(). I checked on BreakPacket, and szPacket contains bad values.

isn't that what I'm doing with the HIBYTE/LOBYTE crap?

Frankly, no.

Note what Salem REALLY said: "you need to display it in hex mode". As in, in the debugger you have it display the value in hex, not as a string.