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digitalmars.D.learn - Create C header files from

reply MaxNaderer <maximilian.wallinger gmail.com> writes:
Hello guys,

so how do we generate C header files automatically for a library 
compiled with dmd, ldc
in betterC. Like basic example below. I found the "-HC" flag 
which can be used to output C++ header files. Do I need to 
convert those manually to C?

```D

export extern(C) {

     uint add(uint a, uint b) {
         return a + b;
     }

}
Feb 16
parent reply Lance Bachmeier <no spam.net> writes:
On Monday, 16 February 2026 at 17:07:53 UTC, MaxNaderer wrote:

 Hello guys,

 so how do we generate C header files automatically for a 
 library compiled with dmd, ldc
 in betterC. Like basic example below. I found the "-HC" flag 
 which can be used to output C++ header files. Do I need to 
 convert those manually to C?

 ```D

 export extern(C) {

     uint add(uint a, uint b) {
         return a + b;
     }

 }


```
dmd -c mycode.c -Hf=mycode.di
```

https://dlang.org/spec/importc.html#ctod

If you want to output the function bodies as D code, add 
`-inline`:

```
dmd -c mycode.c -inline -Hf=mycode.di
```
Feb 16
parent reply Lance Bachmeier <no spam.net> writes:
On Monday, 16 February 2026 at 20:04:36 UTC, Lance Bachmeier 
wrote:

 On Monday, 16 February 2026 at 17:07:53 UTC, MaxNaderer wrote:

 Hello guys,

 so how do we generate C header files automatically for a 
 library compiled with dmd, ldc
 in betterC. Like basic example below. I found the "-HC" flag 
 which can be used to output C++ header files. Do I need to 
 convert those manually to C?

 ```D

 export extern(C) {

     uint add(uint a, uint b) {
         return a + b;
     }

 }


 ```
 dmd -c mycode.c -Hf=mycode.di
 ```

 https://dlang.org/spec/importc.html#ctod

 If you want to output the function bodies as D code, add 
 `-inline`:

 ```
 dmd -c mycode.c -inline -Hf=mycode.di
 ```


Oh sorry. I think you mean you are compiling D code to be called 
from C.
Feb 16
parent reply MaxNaderer <maximilian.wallinger gmail.com> writes:
On Monday, 16 February 2026 at 20:06:52 UTC, Lance Bachmeier 
wrote:

 On Monday, 16 February 2026 at 20:04:36 UTC, Lance Bachmeier 
 wrote:

 On Monday, 16 February 2026 at 17:07:53 UTC, MaxNaderer wrote:

 Hello guys,

 so how do we generate C header files automatically for a 
 library compiled with dmd, ldc
 in betterC. Like basic example below. I found the "-HC" flag 
 which can be used to output C++ header files. Do I need to 
 convert those manually to C?

 ```D

 export extern(C) {

     uint add(uint a, uint b) {
         return a + b;
     }

 }


 ```
 dmd -c mycode.c -Hf=mycode.di
 ```

 https://dlang.org/spec/importc.html#ctod

 If you want to output the function bodies as D code, add 
 `-inline`:

 ```
 dmd -c mycode.c -inline -Hf=mycode.di
 ```


 Oh sorry. I think you mean you are compiling D code to be 
 called from C.


Thank you for your answer. Yes I am going the other way. I create 
the lib in D and want to create a C header and other bindings. It 
should be a lib usable from many other languages like raylib but 
with the power of D!

I have looked into __traits and I guess i need to go this way.
The perfect way would be to get a XML or json from the functions 
so that the bindings can be easily automated
Feb 17
parent Dennis <dkorpel gmail.com> writes:
On Tuesday, 17 February 2026 at 15:27:20 UTC, MaxNaderer wrote:

 I have looked into __traits and I guess i need to go this way.


You can use traits, I've done something like that for Pascal 
instead of C. It roughly looks like:

```D
string headerFromDModules(modules...)()
{
	string result = "#pragma once\n";

	foreach (mod; modules)
	{
		foreach (mem; __traits(allMembers, mod))
		{
			static if (is(typeof(__traits(getMember, mod, mem)) == 
function))
			{
				alias F = __traits(getMember, mod, mem);
				static if (functionLinkage!F == "C")
				{
					result ~= functionToHeader!(mem, F);
				}
			}
		}
	}

	result ~= "\n";
	return result;
}
```

`string functionToHeader(string mem, alias F)()` then has to 
introspect Parameters!F, ParameterIdentifierTuple!F, 
ParameterStorageClassTuple!F, and ReturnType!F and generate a C 
string accordingly. It can be used like so:


```D
import pkg.a;
import pkg.b;

import std;

void main()
{
     File("header.h", "w").write(headerFromDModules!(pkg.a, pkg.b);
}
```


 The perfect way would be to get a XML or json from the 
 functions so that the bindings can be easily automated


dmd has the `-X` flag to generate JSON which I'd wager has 
sufficient information to generate C headers, but you can also 
open an enhancement request in the issue tracker 
(https://github.com/dlang/dmd/issues) to make dmd directly 
generate C headers because it sounds like a worthwhile feature.
Feb 17