On 5/6/2011 9:19 PM, Steven Schveighoffer wrote:
On Fri, 06 May 2011 05:56:17 -0400, Mike Parker <aldac...@gmail.com> wrote:Testing out a new binding I knocked up for a C library. One of the functions takes a struct by value. It looks somewhat like this: struct S {} struct Color { float r,g,b,a; } extern C void function(S* s, Color color, int x, int y, in char*) draw_text; Now, there is another function that adjusts color values when making a color. In C, it is sometimes used like so: draw_text(s, map_color(255, 0, 0, 0), 0, 0, "Blarg"); When I'm calling draw_text like this on the D side, my text output is corrupt. I keep getting weird things like ^^P^, but in the appropriate color. It's consistent, no matter what string I pass, but is different for each color value. If I call draw_text like this: auto color = map_color(...); draw_text(s, color, 0, 0, "Blarg"); It works as expected. Has anyone else seen this, or know of a workaround? I'm going to dig through bugzilla later on and see if it's been reported already, but I'm curious if anyone knows of the cause off hand.There are two possible causes I can think of, depending on how draw_text is defined in C. 1. is it truly a function pointer? That is, does the definition look like void (*draw_text)(S* s, ...), or is it just void draw_text(S* s, ...)?
It's a pointer to a function symbol in a DLL. In Derelict, all functions are pointers on the D side, since the shared libraries are loaded manually. I've bound several C libs in the same way and never encountered this before.
2. It's possible that the extern C (BTW, I thought it had to be extern(C)?) is only applying to the symbol name draw_text and not the function type.
Yeah, that's a typo in my post. It's definitely declared as extern(C) in the source. And I checked with the pragma given below to make sure.
If you answer no to #1, then your problem is your draw_text definition in D. It should look like this: extern(C) void draw_text(S * s, Color color, int x, int y, in char *); If you answer yes to #1, then to check what type the compiler is giving to draw text, do: pragma(msg, (typeof(draw_text)).stringof); This hopefully tells you that it's extern(C), but if not, that is likely the problem. If that's not it, I have no idea ;)
Thanks for the guesses. I don't believe any of the libraries I've bound before now have any functions that take a struct by value. If they have, I haven't had occasion to use them yet. So I wonder if this is an issue with how the compiler handles returning a value struct from a function. Could there be a difference in how it's pushed on to the stack in a D function call versus how it's expected in C? Just grasping.
