Hi,

What is the recommended documentation or introductory material on how to call C libraries from D? I've seen it done in GtkD (for GTK3) and I have heard of -betterC, but it's all a little overwhelming. (I'm an experienced C programmer but new to D)

Cheers,
Ian

On Thursday, 20 February 2025 at 20:09:29 UTC, Ian wrote:

Normally, you should be using ImportC. Look at the quick example from the spec: https://dlang.org/spec/importc.html#examples

The first line of hello.c looks like this:

#include <stdio.h>

When ImportC compiles a C file, it runs the C preprocessor and does all the including you need. But rather than stdio.h, you can compile a C file that includes all the C headers you need. That's all you have to do. You can use the usual preprocessor calls like -I by using the -P switch: https://dlang.org/spec/importc.html#auto-cpp

Assuming ImportC works with your C headers, that's everything you need.

If ImportC doesn't work (as may be the case due to C extensions and preprocessor hacks), you should use dpp or dstep: https://dlang.org/spec/importc.html#dpp

On Thursday, 20 February 2025 at 21:05:40 UTC, Lance Bachmeier wrote:

#include <stdio.h>

Perfect! I'll try this. Thank you.

On Thursday, 20 February 2025 at 20:09:29 UTC, Ian wrote:

Ian, You do not need importC in order to interface with a C library. A good starting read would be: https://dlang.org/spec/interfaceToC.html

If you know the C code (or C library you want to interface with) it is relatively easy to use it directly from D. The real challenge sometimes is to "port" complex C macros to D. The following page is an essential read: https://dlang.org/articles/ctod.html

Here is a simple start project. Let's call liblz4's LZ4_versionNumber() function to get the version of the library, and print it out:

module lz4version;

import std.stdio;

// https://github.com/lz4/lz4/blob/dev/lib/lz4.h line 142
extern(C) int LZ4_versionNumber();

int main() {
    int lz4Version = LZ4_versionNumber();

    int m = lz4Version / 10000;
    lz4Version = lz4Version % 10000;
    int n = lz4Version / 100;
    lz4Version = lz4Version % 100;
    int r = lz4Version;

    writeln("LZ4 library version: ", m, ".", n, ".",r);

    return 0;
}

Save this code to the lz4version.d file, and let's compile and link to lz4version executable with:

gdc -o lz4version lz4version.d -llz4

Now, let's run it:

shell» ./lz4version
LZ4 library version: 1.9.4

Indeed that is the version of the LZ4 library I have on my local Fedora 40 workstation: /usr/lib64/liblz4.so.1.9.4

On Thursday, 20 February 2025 at 21:10:29 UTC, Ian wrote:

Another cool aspect of ImportC is that you can use the D compiler's header generator to generate .di files from C sources - i.e. semi-automatic, native binding generation!

I say semi-automatic since it misses out things like macros, and unfortunately the header generator actually spits out invalid D code...

e.g. I have a script here to generate bindings for libsodium.