CODEWITHSUNDEEP
c++memorygccg++variable-length-array
void-pointer
void-pointer

Reputation: 14827

Undocumented GCC Extension: VLA in struct

While reading the Clang documentation, I came across the following intriguing tidbit: [1]

clang does not support the gcc extension that allows variable-length arrays in structures. This is for a few reasons: one, it is tricky to implement, two, the extension is completely undocumented, and three, the extension appears to be rarely used. Note that clang does support flexible array members (arrays with a zero or unspecified size at the end of a structure).

How can this extension be used? My understanding is that using alloca within a constructor causes the stack pointer to be restored at the end of the calling function, which in this case would be the constructor -- not at the end of the enclosing struct.

Thanks for the help!

Upvotes: 12

Views: 4503

Answers (1)

Jonathan Wakely
Jonathan Wakely

Reputation: 171383

See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37428

and also http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42121

Yes, it's weird.

Upvotes: 7

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