Showing results for Code - The Old New Thing

May 24, 2006
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Beware the C++ implicit conversion

Raymond Chen
Raymond Chen

Today's topic was inspired by a question from a customer: I am working on a stack overflow bug. To reduce the size of the stack frame, I removed as many local variables as I could, but there's still a a lot of stack space that I can't account for. What else lives on the stack aside from local variables, parameters, saved registers, and the retur...

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May 22, 2006
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How do I write a regular expression that matches an IPv4 dotted address?

Raymond Chen
Raymond Chen

Writing a regular expression that matches an IPv4 dotted address is either easy or hard, depending on how good a job you want to do. In fact, to make things easier, let's match only the decimal dotted notation, leaving out the hexadecimal variant, as well as the non-dotted variants. For the purpose of this discussion, I'll restrict myself to the...

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May 19, 2006
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Redirecting output can result in altered program behavior

Raymond Chen
Raymond Chen

Consider a program whose output to the console goes like this. (I've prefixed each line with the output stream.) You want to capture both the normal and error streams, so you run the program and append "" to capture both streams into a single file. But when you look at the resulting output file, you get this: What happened? Most programs c...

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May 16, 2006
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The real scoop on the the x64 calling convention on 64-bit Windows

Raymond Chen
Raymond Chen

Official (though preliminary) documentation on the x64 calling convention is available on MSDN, for those who want more than my quack overview. (Oops, I meant "quick overview". Little Freudian slip there.)

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May 3, 2006
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The alertable wait is the non-GUI analog to pumping messages

Raymond Chen
Raymond Chen

When you are doing GUI programming, you well know that the message pump is the primary way of receiving and dispatching messages. The non-GUI analog to the message pump is the alertable wait. A user-mode APC is a request for a function to run on a thread in user mode. You can explicitly queue an APC to a thread with the function, or you can do ...

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May 2, 2006
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A cache with a bad policy is another name for a memory leak

Raymond Chen
Raymond Chen

A common performance trick is to reduce time spent in the heap manager by caching the last item freed (or maybe the last few) so that a subsequent allocation can just re-use the item rather than having to go make a new one. But you need to be careful how you do this or you can end up making things worse rather than better. Here's an example motiva...

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May 1, 2006
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What's so special about bitmaps and DCs?

Raymond Chen
Raymond Chen

You can select pens, brushes, fonts and bitmaps into a DC with the function, and from this list, bitmaps are special. Because, if you look carefully, bitmaps are the only modifiable objects on the list. Pens, brushes and fonts cannot be modified once they are created. But bitmaps, oh, bitmaps. A bitmap selected into a DC changes as you draw into ...

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Apr 28, 2006
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What does CS_SAVEBITS do?

Raymond Chen
Raymond Chen

If you specify the class style, then the window manager will try to save the bits covered by the window. But the real question is why, because that is your guide to using this power only for good, not for evil. When a window whose class specifies the class style is displayed, the window manager takes a snapshot of the pixels on the screen where ...

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Apr 25, 2006
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No, really, you need to pass all unhandled messages to DefWindowProc

Raymond Chen
Raymond Chen

Earlier I had discussed that you have to return the special value if you want to deny a device removal query because too many programs thought that they had covered "all" the Windows messages and just returned zero for the others. Since then, there have been lots of other window messages added to the system, many of which contain nontrivial proce...

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Apr 18, 2006
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How to fill in that number grouping member of NUMBERFMT

Raymond Chen
Raymond Chen

If you look at the structure, the way groups are expressed by the member do not match the value returned by : expresses grouping as a series of semicolon-separated numbers, each expressing the number of digits in each group (least-significant group first). A trailing zero indicates that the last grouping should be repeated indefinitely. For ex...

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