Linking D with C structs

[Anthony]

Hello,


I'm trying to hand write some bindings to mongo-c-driver. (For 
learning purposes and to get the latest bindings).

My binding code to convert <mongoc/mongoc.h> to mongoc/mongoc.d 
is:

===== c interop file ====
module mongoc/mongoc.d;
import core.stdc.stdint;

extern (c) {
struct {
     uint domain;
     uint code;
     char[504] message; //when this exists, the code does not 
compile
}
}
=======================

===== build script ====

export 
LD_LIBRARY_PATH=mongo-c-driver/cmake-build/src/libmongoc:mongo-c-driver/cmake-build/src/libbson:$LD_LIBRARY_PATH

dmd hello_mongo.d \
     -I=mongo-c-driver/src/libmongoc/src/ \
     -I=mongo-c-driver/src/libbson/src/ \
     -I=mongo-c-driver/cmake-build/src/libbson/src/bson/ \
     -I=mongo-c-driver/cmake-build/src/libmongoc/src/mongoc \
     -L=-Lmongo-c-driver/cmake-build/src/libmongoc \
     -L=-Lmongo-c-driver/cmake-build/src/libbson \
     -L=-lmongoc-1.0 \
     -L=-lbson-1.0 \

./hello_mongo
========================


However, when I add the message field in the struct, I cannot 
compile the code:

ld: hello_mongo.o: in function `_Dmain':
hello_mongo.d:(.text._Dmain[_Dmain]+0x1a): undefined reference to 
`_D6mongoc6mongoc13_bson_error_t6__initZ'


What does "__initZ" refer to?
Does this refer to automatic initialization like "this()"?