On 05/10/2013 06:04 PM, Skirmantas Kligys wrote:
I am trying to write a native wrapper for
https://github.com/pascalj/rust-expat
(BTW, if there is a native Rust XML parser, I am interested to hear
about it, did not find it). I have trouble calling back into Rust
from C code:
fn set_element_handlers(parser: expat::XML_Parser, start_handler:
&fn(tag: &str, attrs: &[@str]), end_handler: &fn(tag: &str)) {
let start_cb = |_user_data: *c_void, c_name: *c_char, _c_attrs: **c_char| {
unsafe {
let name = str::raw::from_c_str(c_name);
start_handler(name, []);
}
};
let end_cb = |_user_data: *c_void, c_name: *c_char| {
unsafe {
let name = str::raw::from_c_str(c_name);
end_handler(name);
}
};
expat::XML_SetElementHandler(parser, start_cb, end_cb);
}
This says that it saw &fn... instead of expected extern fn for the
second and third parameter. Any ideas how to do this?
You need a function type that is compatible with C. Here `start_cb` is a
Rust closure, using the Rust ABI, but you need it to be a C function
pointer. It should be defined more like
extern fn start_cb(user_data: *c_void, c_name: *c_char, c_attrs:
**c_char) { ... }
The `extern` says that it uses a foreign ABI, C by default. You can take
a value to it like
let start: *u8 = start_cb;
Note that the extern fn has type *u8. This is a temporary hack.
Eventually it will have type `extern "C" fn(...)`.
Then your XML_SetElementHandler can be defined like `fn
XML_SetELementHandler(parser: Parser, start_cb: *u8, end_cb: *u8)`.
Good luck.
-Brian
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