Variable used without being initialized?

[krmed]

A couple of things I notice about your code...

First, in your if

if (SQLInitTimer1 = false)
{
	QueryPerformanceCounter(&SQLStrtTime);
	SQLInitTimer1 = true;
}

you really need

if (SQLInitTimer1 == false)

and instead of

else if (SQLInitTimer1 = true)

you need

else if (SQLInitTimer1 == true)

Secondly, in this block

if (SQLInitTimer1 == false)
{
	QueryPerformanceCounter(&SQLStrtTime);
	SQLInitTimer1 = true;
}
else if (SQLInitTimer1 == true)
{
	QueryPerformanceCounter(&SQLCurrTime);
	QueryPerformanceFrequency(&SQLFreq);
	SQLDiff = ((double)(SQLCurrTime.QuadPart - SQLStrtTime.QuadPart) / (double)(SQLFreq.QuadPart)) * 1000; 
	if (SQLDiff >= 500)
	{
		UpdateSQL();
		SQLInitTimer1 = false;
	}
}

If the initial state of SQLInitTime1 is not false, you will fall directly into your else if and SQLStartTime has not yet been initialized.

Hope that helps.

PS - Indentation and the use of code tags would really help you see the flow.