Question

I’m working with some old code, trying to improve it, and I came across the following, which I am having trouble understanding:

controlToUpdate.Font = 
    new System.Drawing.Font(someFont,
                            someFontSize,
                            controlToUpdate.Font.Style ^ 
                                (controlToUpdate.Font.Style & FontStyle.Bold));

Specifically, I am confused as to what the last parameter does. As I understand it, the following should do a bitwise comparison, and return the result:

controlToUpdate.Font.Style ^ (controlToUpdate.Font.Style & FontStyle.Bold)

..but what does that mean in this situation? What are the possible results, that may be passed as the third parameter to new Font(...), and how can I rewrite this more clearly, while keeping with the intent of the original programmer?

Sidenote: Is this a normal way to do things when working with Windows Forms? I’m a little new in that area – is the intent here obvious to coders more experienced in this field?

Answer 1

controlToUpdate.Font.Style & FontStyle.Bold

performs an “and” to return FontStyle.Bold if the style (controlToUpdate.Font.Style) includes bold, and 0 if the style does not include bold: basically, it gets just the “bold” bit.

controlToUpdate.Font.Style ^ (controlToUpdate.Font.Style & FontStyle.Bold)

performs an “xor”; if the bold bit was set, it removes it; if the bold bit was not set, then it does nothing (since “xor” with 0 is a no-op).

So basically, that complicated code just removes the “bold” bit (if it is set). A simpler implementation would have been:

controlToUpdate.Font.Style & ~FontStyle.Bold

How that works: here, the ~FontStyle.Bold inverts all the bits; FontStyle.Bold is 1:

000....000001

so ~FontStyle.Bold is:

111...1111110

we then “and” that with our current style, which means it keeps all of the old style except the bold-bit.