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Initializing a struct

Just saw something in some of Raymond Chen’s sample code that made me go "Wha…?!?" in a good way. It’s a line where he initializes a classic Windows struct, MONITORINFO, which like a lot of windows structs starts with a cbSize value [to hold the structures byte size— used as a kind of version/error check].

Normally in such instances I would write [with a sigh]:

MONITORINFO mi;
ZeroMemory(&mi, sizeof(mi));
mi.cbSize = sizeof(mi);

Whereas I noticed that Raymond wrote:

MONITORINFO mi = { sizeof(mi) };

which achieves exactly the same effect incredibly neatly! I can’t believe I was unaware of this technique [specifically the fact that even though only the first value is specified, the entire struct in initialized to zero]. Brilliant! And you don’t even have to know the name of the stupid cbSize member!

BTW: I know I’m not the only one who uses [until now] the tedious long form— If you are a C/C++ person I hope this tidbit can save you valuable seconds as well. And if you are a legend who already uses the short form, please don’t think less of me for not seeing it myself… ;)

This entry was posted on Sunday, May 15th, 2005 at 11:15 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

2 Responses to “Initializing a struct”

  1. Xavier Says:
    August 11th, 2005 at 2:23 am

    Huh … i cannot understand how cbsSize is initialized in the second case … I can understand that the strcture is zeroed and the first member is set to sizeof(mi), but for cbSize … only if cbSize happends to be the first member ?

    Any hint ?

    ( i’m lost )

  2. mark Says:
    August 11th, 2005 at 2:38 am

    yes, cbSize [or any other struct size] is always first member, although this is purely by convention

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