On Thu, 09 Dec 2010 09:37:03 -0500, CrypticMetaphor <crypticmetapho...@gmail.com> wrote:

I found this page that describes how to call c functions from D.

I found this page that describes how:

on that page he uses gcc, and I use dmc, but I get different results. This is what I did

// cfile.c file
extern int globalFromD;

void functionFromC(int a) {
    globalFromD = a;
// end cfile.c

// dfile.d
extern(C) { // this is needed to make it available from C
         int globalFromD;
extern(C) { // also needed when listing the prototypes for your C functions
         void functionFromC(int);

import std.stdio; // for writefln

int main() {
         globalFromD = 100;
         writefln("%d", globalFromD);

         writefln("%d", globalFromD);

         return 0;
// end dfile.d

I compile with:
dmc -c cfile.c
And I get  an cfile.obj, which is the object code (.o in gcc).
Then I compile the D code
dmd dfile.d cfile.obj
and I get no errors, so I run it, the result:
// start result

// end result

Why is it still 100? It should be 500. I don't think functionFromC( int ) is being called, and I can't really find any other sources that clearly explain how to do this simple stuff, so can anyone explain how to fix it?

I'm guessing that this is a later D2 compiler? If so, then the default storage for globals is in Thread Local Storage (local to each thread). This could explain why it doesn't work, because globalFromD is in TLS in D-land, but in the normal global space in C-land. But there is no declaration of the global-space version then, so I'm surprised it would compile then.

I'm really curious why this doesn't work but does compile.

What version of D compiler are you using?

When using dmd 2.050 on linux I get this error when compiling:

ste...@steve-laptop:~/testd$ gcc -c testc.c
ste...@steve-laptop:~/testd$ ~/dmd-2.050/linux/bin/dmd testcallc.d testc.o
/usr/bin/ld: globalFromD: TLS definition in testcallc.o section .tbss mismatches non-TLS reference in testc.o
testc.o: could not read symbols: Bad value
collect2: ld returned 1 exit status
--- errorlevel 1

Maybe it's a bug in Windows dmd?


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