Zig "translate c" doesn't translate main function

Question

I created a C file:

int main() {
  return 1;
}

I used Zig's translate-c command line option to generate a zig file, and I only get some global variable declarations like

pub const __GCC_ATOMIC_TEST_AND_SET_TRUEVAL = 1;
pub const __FLT16_MAX_EXP__ = 15;
pub const __BIGGEST_ALIGNMENT__ = 16;
pub const __SIZEOF_FLOAT__ = 4;
pub const __INT64_FMTd__ = c"ld";
pub const __STDC_VERSION__ = c_long(201112);
... // and many

And no main function is found. But if I change the function name to myFunction like this:

int myFunction(int a) {
  return a;
}

A function appears when I re-generate it:

pub export fn myFunction(a: c_int) c_int {
    return a;
}

Am I missing something? What's the rule of zig's translate-c function?

Did you create the tag `zig`? If so you might want to give it a short desciption in the wiki. — Kami Kaze, Apr 18 '18 at 06:17
I don't know about zig. But return 1 seems like the compiler would just replace the function call with 1. — Kami Kaze, Apr 18 '18 at 06:18
@KamiKaze Yes I did and the wiki edit is awaiting peer review. — ice1000, Apr 18 '18 at 06:23
have you tried replacing the main function with something that is not deterministic at compile time? — Kami Kaze, Apr 18 '18 at 06:34
...e.g. `int main() { int a; scanf("%d", a); return a;`. Now, the compiler cannot forsee/optimize the result of `main()`. — Scheff's Cat, Apr 18 '18 at 06:43
@KamiKaze Yes, I've found this! The "constexpr" like functions are optimized! Thanks guys. — ice1000, Apr 18 '18 at 06:52
Zig now supports this example and I've updated my answer to reflect that. — andrewrk, Feb 19 '19 at 19:58

andrewrk · Accepted Answer · 2019-02-19T19:57:27.313

When this question was asked, translate-c did not yet support functions with unspecified parameters. This was visible by using --verbose-cimport:

test.c:1:5: warning: unsupported type: 'FunctionNoProto'
test.c:1:5: warning: unable to resolve prototype of function 'main'

In C, if you leave the parameters empty, it's not actually zero parameters, it's unspecified. You have to use void to mean "no parameters".

So that's why the second example worked - because the parameter list was not empty.

However as of e280dce3, Zig supports translating C functions with unspecified parameters, and the example from the question turns into this Zig code:

pub export fn main() c_int {
    return 1;
}

Zig "translate c" doesn't translate main function

1 Answers1