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215 Stars 23 Forks BSD 3-Clause "New" or "Revised" License 1.6K Commits 87 Opened issues


A C compiler written in Rust, with a focus on good error messages.

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saltwater: the part of the sea causing lots of rust

A C compiler written in Rust, with a focus on good error messages.


reads from standard in by default, so you can type in code directly. It's not interactive though, you have to hit Ctrl+D to indicate end of file (Ctrl+Z on Windows).


swcc --help
for all options (or see below).

Running on Windows

You need to have

on your PATH. You can either install mingw + gcc or MSVC. Other than that, it should work exactly the same as on Linux.


brew install saltwater

Unimplemented features

  • Defining functions taking variadic arguments. Note that calling variadic functions (like
    ) is already supported.
  • Variable-length arrays (
    int a[n]
  • Multiple translation units (files)
  • Bitfields
  • Compiling on non-x86 platforms
  • Cross-compilation


$ cat tests/runner-tests/readme.c
// output: j is 6
int printf(const char *, ...);

typedef struct s *sp;

int i = 1; int a[3] = {1, 2, 3}; float f = 2.5;

struct s { int outer; } my_struct;

int g(int);

int main(void) { sp my_struct_pointer = &my_struct; const int c = my_struct_pointer->outer = 4; // should return 6 int j = i + f*a[2] - c/g(1); printf("j is %d\n", j); return j; }

int g(int i) { if (i < 0 || i >= 3) { return 0; } return a[i]; } $ swcc tests/runner-tests/readme.c $️ ./a.out j is 6

Debug output

$ cat tests/runner-tests/cpp/if/defined.c
// code: 2

#define a #define b

#if defined(a) int i = 2; #endif

#ifndef b syntax error #endif

if defined b && defined(a)

int main() { return i; }

#endif $ swcc -E tests/runner-tests/cpp/if/defined.c int i = 2 ; int main ( ) { return i ; }

$ echo 'int i = 1 + 2 ^ 3 % 5 / 2 & 1; int main(){}' | swcc --debug-ast
ast: int i = ((1) + (2)) ^ ((((3) % (5)) / (2)) & (1));
ast: int main(){
$ cat tests/runner-tests/hello_world.c
int main() {
    puts("Hello, world!");
$ swcc --debug-ir tests/runner-tests/hello_world.c
function u0:0() -> i32 system_v {
    gv0 = symbol colocated u1:3
    sig0 = (i64) -> i32 system_v
    fn0 = u0:26 sig0

block0: v0 = global_value.i64 gv0 v1 = call fn0(v0) v2 = iconst.i32 0 return v2 } $ ./a.out Hello, world! </stdio.h>

All options

$ swcc --help
swcc 0.9.0
Joshua Nelson 
A C compiler written in Rust, with a focus on good error messages.

usage: swcc [FLAGS] [OPTIONS] []

FLAGS: --debug-ast If set, print the parsed abstract syntax tree (AST) in addition to compiling. The AST does no type checking or validation, it only parses. --debug-hir If set, print the high intermediate representation (HIR) in addition to compiling. This does type checking and validation and also desugars various expressions. --debug-ir If set, print the intermediate representation (IR) of the program in addition to compiling. --debug-lex If set, print all tokens found by the lexer in addition to compiling. --jit If set, will use JIT compilation for C code and instantly run compiled code (No files produced). NOTE: this option only works if swcc was compiled with the jit feature. -h, --help Prints help information -c, --no-link If set, compile and assemble but do not link. Object file is machine-dependent. -E, --preprocess-only If set, preprocess only, but do not do anything else. Note that preprocessing discards whitespace and comments. There is not currently a way to disable this behavior. -V, --version Prints version information

OPTIONS: --color When to use color. May be "never", "auto", or "always". [default: auto] -o, --output The output file to use. [default: a.out] --max-errors The maximum number of errors to allow before giving up. Use 0 to allow unlimited errors. [default: 10] -I, --include

Add a directory to the local include path (#include "file.h"). Can be specified multiple times to add multiple directories. -D, --define Define an object-like macro. Can be specified multiple times to add multiple macros. val defaults to 1.

ARGS: The file to read C source from. "-" means stdin (use ./- to read a file called '-'). Only one file at a time is currently accepted. [default: -]


cargo test
# optionally, you can fuzz the compiler
# it may be more helpful to just `grep -R unimplemented src`, though




Running Honggfuzz locally requires some parameters to use it at its full potential,

so it is probably a good idea to have a look here:

and here:

we suggest the following:

HFUZZ_RUN_ARGS="--tmout_sigvtalrm --exit_upon_crash" tests/



Implementation Defined Behavior



See This also includes reporting bugs.

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