C to D code converter

A tool that does the boring parts of translating C to D.

Try it in your browser!

YouTube: DConf Online '22 - Translating C to D

Usage

From the root of this repository:

dub run --arch=x86_64 -- ../test/main.c

Arguments are .c or .h files, for which it outputs a translated .d file next to it. This .d file may not compile yet, but it's supposed to get you 90% there. The remaining errors are usually because of non-trivial macros, initializers, or because of D's stricter type system.

Compatibility

The program depends on C libraries that are currently included in binary form in the /lib folder for x86-64 Windows and Linux. By editing the makefile and running make you might make it work for other platforms as well. In the future the aim is to use ImportC for this.

Installation

You can copy the built binary to a folder in your PATH, for example on linux:

dub build
sudo cp build/ctod /usr/local/bin/

This allows you to simply invoke ctod from anywhere.

Motivation

This was written before ImportC. Statically linking C libraries with dub is clumsy: while there's usually C bindings in the package repository, you still need to grab release binaries for each build target / configration, include them in the repo, and fiddle with dub flags until there are no linker errors anymore.

That's why I like to translate C code to D. While this requires some intelligence, a lot of the work is simple syntactic find-and-replace actions, and converting declaration syntax. Even with VIM macros it was getting tedious, so I wrote this tool. I used it for translating glfw and libsoundio, as well as some single-file C libs.

How it works

The tree-sitter parser for C is used to parse C code, including macros. tree-sitter is a parser generator with a focus on incremental parsing and error recovery, useful for IDE tools. Error recovery is particularly useful for this tool: it always gives a best-effort translated output, even when it encounters what it thinks is a parse error. If you want, you can convert broken C code to similarly broken D code.

This tool makes use of the fact that in general, if D code looks like C, it either behaves the same as C or doesn't compile. Also, D has almost all features that C has. The tool doesn't need a deep understanding of C code, and a lot of things are passed through without any change:

// Identical in both C and D
float fabs(float x) {
    if (x < 0.0)
        return -x;
    return x;
}

However, there's also a lot of things that are different between C and D. This ranges from simple syntax changes:

• x->y => x.y
• (float) 1lu => cast(float) 1Lu
• "con" "cat" => "con" ~ "cat"

To more difficult translations, such as declarations with complex types:

char *(*(*fun)[5])(int);

D:

char* function(int)[5]* fun;

It's being developed like this:

• Run ctod on a C file
• Look at the output, notice something that needs to be adjusted to be valid D
• Enter the C code in the tree-sitter playground to see what it looks like in the AST
• Add code to recognize and translate the pattern
• Repeat for as many patterns as possible

So this is really just a big find-and-replace tool that operates on an AST provided by tree-sitter.

You can take a look at testcases.md to see the capabilities of ctod.

Alternatives

If you only need to translate C headers and not actual code, there are also these tools available:

• dpp
• dstep
• ohmygentool

Those tools use libclang (the LLVM C parser api) to parse C instead of tree-sitter.

See also

• Programming in D for C Programmers