ccomptime

This software is unfinished

A drop-in replacement for clang that adds compile-time code execution to C.

Overview

ccomptime allows you to run C code at compile time using comptime, inline_comptime directives. The code executes during compilation and can generate code, files, and anything really. You keep all the footguns C gives you even during compilation time!

Usage

Building

cc nob.c -o nob
./nob

Using as compiler

Prepend your clang command with the ccomptime cli. Thats it, ccomptime will "highjack" the compilation process

./ccomptime clang -o program test/main.c

Syntax

Compile-time execution:

comptime {
    printf("This runs at compile time!\n");
}

Example

#include "ccomptime.h"

void generate_file() {
    FILE *f = fopen("generated.h", "w");
    fprintf(f, "#define MAGIC_NUMBER %d\n", 42);
    fclose(f);
}

long long fibo(long long n) {
  if (n <= 1)
    return n;
  long long a = 0, b = 1, c;
  for (long long i = 2; i <= n; i++) {
    c = a + b;
    a = b;
    b = c;
  }
  return b;
}

comptime { generate_file(); }

int main() {
    long long res = comptime_inline_infer(fibo(34 + 35)); // value will be computed at compile time and inlined here

    printf("Res is %llu\n", res);
    return 0;
}

The compile-time code runs during compilation, generating generated.h before the final binary is built.

How it works

1. Preprocesses source files to find comptime blocks
2. Extracts compile-time code into a separate "runner" program
3. Compiles and executes the runner to generate replacements
4. Rewrites the original source with results
5. Compiles the final program with regular clang

Related Projects

While several languages and tools offer compile-time execution, ccomptime is unique in bringing full compile-time code execution to C:

Similar Approaches

• Zig's comptime - Built-in compile-time execution with similar capabilities, but requires using Zig
• C++ constexpr - Compile-time function evaluation, but limited to pure functions (no I/O)
• Template metaprogramming - C++ templates can generate code, but with complex syntax and limited scope
• Build system generators - Tools like CMake or custom scripts, but separate from compilation

What Makes This Different

• True compile-time execution in C - Full C language access during compilation
• I/O capabilities - Can generate files, network requests, or any operation (unlike constexpr)
• Drop-in replacement - Works with existing C codebases without language changes
• Integrated compilation - Part of the compilation process, not a separate build step