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Comment by jstanley | Hacker News Reader

Anybody know what the:

  int needfid[] = {
	[Tversion] 0,
	[Tflush] 0,
	[Tauth] 0,

syntax means? Is this some Plan 9 extension, or is it just something I've never encountered?

EDIT: I guess the value in the []'s is the array index to set the value of.

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A variation of this syntax was standardized in C99:

    int needfid[] = {
        [Tversion] = 0,
        [Tflush] = 0,

It works for structs too:

    struct blah needfid = {
        .version = 0,
        .flush = 0,

That's right, it's a designated initializer, except the standard c99 way requires an =. gcc didn't/doesn't but that's nonstandard. So it is an extension, just not a plan9 one - a gcc-ism. clang's error/warning, as usual, is very helpful so it's worth it just to try clang when running into weirdness like that:

    warning: use of GNU 'missing =' extension in designator
          [-Wgnu-designator]

Well, it is a Plan 9 extension. You made it sound like it was only a gcc extension.

You're right, it's described in 3.5 of

http://plan9.bell-labs.com/sys/doc/compiler.html

It seems like it was contemporaneous with the proposed c90 extension and also supported the = except optionally. But it was definitely something in the plan 9 compiler rather than only a gcc thing.

> Is this some Plan 9 extension, or is it just something I've never encountered?

It's C99 (I also only saw it in C99 articles, never in production code). See http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Designated-Inits...

It's heavily used in the Linux kernel and in the Linux world in general. But Visual Studio doesn't support it, so projects that target Windows pretty much have to avoid it.

See "3.5 Initialization indexes": http://plan9.bell-labs.com/sys/doc/compiler.html

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