Interfacing to C. extern (C) variables

[Jimmy Cao]

On Sun, Jun 26, 2011 at 5:00 PM, Alex_Dovhal <alex_dovhal at yahoo.com> wrote:

> "Robert Clipsham" <robert at octarineparrot.com> wrote:
> > On 26/06/2011 20:54, Alex_Dovhal wrote:
> >> I'd like to call C functions and use C variables in D module.
> >> D calls C functions just fine, but how can I use C variables?
> >
> > extern(C) extern int myCVar;
>
> Thanks for answer. I've already tried that, it doesn't work for some
> reason:
>
> * file unit2.d:
> module unit;
> import std.stdio;
> extern(C) int func();
> extern(C) extern int c_var;
>
> void main()
> {
>    func();
>    writeln("In D");
>    writefln("c_var = %d", c_var);
>    writefln("&c_var = %x", &c_var);
> }
>
> Result:
> In C
> c_var = 1234
> &c_var = 470200
> In D
> object.Error: Access Violation
> ----------------
> 426DA4
> 426C1B
> 405BEB
> 4057E7
> 451099
> ----------------
>
>
> Found workaround, but it's extreme hack:
>
> *file test.c
> #include <stdio.h>
> int c_var;
> //int* ref_c_var()
> //{
> //    return &c_var;
> //}
>
> #define REF_DECL(type, name) type* ref_ ## name () {return &name;}
>
> REF_DECL(int, c_var)
>
> int func()
> {
>    c_var = 1234;
>    printf("In C\n");
>    printf("c_var = %d\n", c_var);
>    printf("&c_var = %x\n", &c_var);
>    return 0;
> }
>
> *file: unit1.d:
> module unit;
> import std.stdio;
>
> extern(C) int func();
>
> string C_VAR(string type, string name)
> {
>    return
>        "extern (C) "~ type ~ "* ref_" ~ name ~ "();"~
>        " " ~ "ref " ~ type ~ " " ~ name ~"(){return *ref_"~name~"();}";
> }
>
> mixin(C_VAR("int", "c_var"));
>
> void main()
> {
>    func();
>    writeln("In D");
>    writefln("c_var = %d", c_var);
>    writefln("&c_var = %x", &c_var);
> }
>
>
>

It works for me like this:

extern(C){
   __gshared int c_var;
   int func();
}
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