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langref: document extern variadic functions #13902

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Dec 13, 2022
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langref: document extern variadic functions #13902

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27 changes: 27 additions & 0 deletions doc/langref.html.in
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Expand Up @@ -10792,6 +10792,33 @@ pub const MAKELOCAL = @compileError("unable to translate C expr: unexpected toke
<p>{#syntax#}ptr_to_struct_array[index].struct_member{#endsyntax#}</p>
{#header_close#}

{#header_open|C Variadic Functions#}
<p>Zig supports extern variadic functions.</p>
{#code_begin|test|variadic_function#}
{#link_libc#}
{#code_verbose_cimport#}
const std = @import("std");
const testing = std.testing;

pub extern "c" fn printf(format: [*:0]const u8, ...) c_int;

test "variadic function" {
try testing.expect(printf("Hello, world!\n") == 14);
try testing.expect(@typeInfo(@TypeOf(printf)).Fn.is_var_args);
}
{#code_end#}
<p>
Non extern variadic functions are currently not implemented, but there
is an accepted proposal. See <a href="https://github.com/ziglang/zig/issues/515">#515</a>.
</p>
{#code_begin|obj_err|non-extern function is variadic#}
export fn printf(format: [*:0]const u8, ...) c_int {
_ = format;

return 0;
}
{#code_end#}
{#header_close#}
{#header_open|Exporting a C Library#}
<p>
One of the primary use cases for Zig is exporting a library with the C ABI for other programming languages
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