On Friday, 22 October 2021 at 05:54:21 UTC, Kirill wrote:
I am not a compiler expert, but I genuinely would like to know
why we have Dmain.
I've been looking at the generated assembly code recently and
noticed the _Dmain function. I didn't notice it before. Then
there is main, where Dmain is called.
Why is that?
The entry point for your program is a function `_start`. That's
implemented in the C runtime, which all D programs depend on. It
in turn calls `main`, as it does for C and C++ programs.
The D compiler generates an `extern(C) main` function that hands
control off to DRuntime for initialization, then in turn calling
your application `main` (a.k.a. `_DMain`).
See:
https://github.com/dlang/druntime/blob/master/src/rt/dmain2.d#L245
If you declare your main function as `extern(C)`, then the
compiler does not generate one and you get handed control from
the C runtime. Which in turn means you have to handle
initialization of the D runtime yourself.
