extern(C) void main()
{
import core.stdc.stdlib : alloca;
enum length = 20;
auto msg = (cast(char*)alloca(length))[0 .. length];
}
https://run.dlang.io/is/dHAqPo
$ dmd -betterC main.d
error: undefined reference to '__alloca'
collect2: error: ld returned 1 exit status
Error: linker exited with status 1
Works fine with LDC, however: https://run.dlang.io/is/m45jG1
Also, `alloca` should not be in `core.stdc.stdlib`; it's not a standard C function.
It may also be better to allocate static arrays on the stack when their length is supplied at runtime. See https://issues.dlang.org/show_bug.cgi?id=18788. That would make `alloca` and `__alloca` just an implementation detail that users wouldn't even need to use directly.
Comment #1 by bugzilla — 2018-08-14T20:13:51Z
alloca() works by calling a compiler-specific function to implement it. This means it has to be customized for each supported C compiler. Currently for dmd, this has only been done for dmc (Win32).
Whether it's standard C or not, functions that are in the corresponding compiler's stdlib.h should be in core.stdc.stdlib.
Comment #2 by robert.schadek — 2024-12-13T19:00:16Z