https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114534
Bug ID: 114534
Summary: Feature request: extend VLA support in C++
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: nightstrike at gmail dot com
Target Milestone: ---
See https://gcc.gnu.org/pipermail/gcc-help/2024-March/143369.html for
reference.
The documentation at https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html
states that VLAs are supported in C++ as an extension.
Compiling the following:
void f(int a, int b[a]);
void f() {
int c[2];
f(2, c);
}
with g++ -std=gnu++20 results in the error: "use of parameter outside function
body before ']' token". The docs say nothing about partial support of VLA,
just that they can be used.
Where this is useful as an extension is in the somewhat reasonable case of
including a C header in a C++ program. If that C header declares a function
using a C99 VLA, it would be awesome if g++ were to accept it in -std=gnu++
mode (and it would be fine if it were rejected in -std=c++ mode). Consider a
situation where you cannot modify the header, and so have to use it as-is.
For comparison, clang added support for this feature in version 12. It would
be advantageous to have feature parity given that it started as a GNU
extension. Moreover, better interoperability with C is useful in its own
right.
