Question

I’m trying to read the install path for an application, and I’m baffled at the behaviour I’m getting. First, here’s the code that didn’t work (formatted it a little so it doesn’t take up a huge line):

LONG status = RegQueryValueEx(
    hkRegistry,
    "InstallPath",
    0,
    &regType, (LPBYTE)installPath,
    &regSize );
if (status == ERROR_SUCCESS) {
    // Handle success.
}

I realized that it was failing on the call to RegQueryValueEx, so I decided to probe the return value by throwing it within an exception by adding:

else {
    throw Exception( status );
}

But then… the code started to work and the call to RegQueryValueEx succeeded. I’ve been able to repeat this behaviour as long as I throw something within the else. If I comment out the body of the else, the error returns.

Edit: Okay, I tried calling MessageBox instead of an exception and I get the same behaviour. If I comment it out, it stops working again.

Is there a rational explanation for this?

Answer 1

It’s possible that the buffer for installPath is too small compared to the value contained in regSize (which must be initialized to the size of the buffer).

If installPath is a stack-allocated value I suspect that it is overflown, causing the value of status to get overwritten.