Re: [Tinycc-devel] Odd problem when using variables defined in header files for a .dll

[grischka]

William Hales wrote:
> Thankyou, but this does not seem to work.  I just tried adding:
>
>     __declspec(dllimport) extern WINDOW *stdscr;
>
> ...to the start of my main.c, and it did not change the resulting program 
> behaviour.  (No warnings or errors either, and I'm using -Wall).
>
> [Screenshot. Let's see if the mailing list supports this.]

Sure that doesn't work, no surprise ;)

Because in C, additional extern declarations for the same symbol (with
the same type) are allowed but do not override any non-extern definitions
before or after.

Therefor you need to change the already existing declaration, that
is in curses.h, just add the single word 'extern' in the right place:

    @@ -395,9 +395,9 @@ typedef struct
     #ifdef PDC_DLL_BUILD
     # ifdef CURSES_LIBRARY
     #  define PDCEX __declspec(dllexport) extern
     # else
    -#  define PDCEX __declspec(dllimport)
    +#  define PDCEX __declspec(dllimport) extern
     # endif
     #else
     # define PDCEX extern
     #endif

     PDCEX  int          LINES;        /* terminal height */
     PDCEX  int          COLS;         /* terminal width */
     PDCEX  WINDOW       *stdscr;      /* the default screen window */

Alternatively you could patch TCC to treat dllimport as extern
automatically (as do mingw or msvc). In tccgen.c:

    @@ -7022,9 +7022,9 @@ static int decl0(int l, int is_for_loop_init)
                 if (ad.a.weak)
                     type.t |= VT_WEAK;
     #ifdef TCC_TARGET_PE
                 if (ad.a.func_import)
    -                type.t |= VT_IMPORT;
    +                type.t |= VT_IMPORT, btype.t |= VT_EXTERN;
                 if (ad.a.func_export)
                     type.t |= VT_EXPORT;
     #endif
                 type.t |= ad.a.visibility << VT_VIS_SHIFT;

(If you want this to be part of the upcoming tcc 0.9.27 release,
feel free to apply such patch to our 'mob' branch).

Which you prefer.

Here is a batch file snippet to build pdcurses and demo with TCC:

    tcc -I. -DPDC_DLL_BUILD -o pdcurses.dll -shared -rdynamic ^
       pdcurses/*.c win32/*.c -include stdlib.h -ladvapi32

    tcc -I. -DPDC_DLL_BUILD -lpdcurses -L. demos/firework.c

    .\firework
    pause

You can also run the demo directly from source code, like this:

    tcc -I. -DPDC_DLL_BUILD -lpdcurses -L. -run demos/firework.c

You can even run the entire pdcurses + demo directly from source code
(which in fact doesn't require any changes to pdcurses or TCC):

    tcc -I. pdcurses/*.c win32/*.c -ladvapi32 -luser32 -run demos/firework.c


(pdcurses from: https://github.com/Bill-Gray/PDCurses/archive/master.zip)

--- grischka

> Regards, Hales

> > William Hales wrote:
> > > Hello,
> > >
> > > I have been having a problem with tcc when linking my project against a dll.  
> > > The dll and my project share variables through a header file.  This works 
> > > fine with gcc, but when compiled with tcc my program and the dll end up with 
> > > completely unique copies of the variables in the .h file, rather than sharing 
> > > them.
> >
> > tcc requires 'extern' on the application (program) side, for example
> >
> >     __declspec(dllimport) extern int foo;
> >
> > -- gr