Playground

extern int printf(const char* fmt, ...);

region Frame { capacity: 4096 }

struct Particle { float x; float v; };

// The region is part of the type: p can't outlive the arena.
void step(&arena<Frame> Particle p, float dt) {
    p.x = p.x + p.v * dt;
}

int main() {
    &arena<Frame> Particle p = new<Frame> Particle;
    p.x = 0.0;
    p.v = 2.5;
    for (int i = 0; i < 3; i = i + 1) {
        step(p, 0.5);
        printf("t=%d x=%.2f\n", i, p.x);
    }
    arena_reset<Frame>();   // O(1): no per-object free, no GC
    return 0;
}

Ctrl/⌘ + Enter runs · Tab indents (Esc, then Tab, moves focus out) · Share puts the program in the URL

About the playground

Examples loads any runnable program from the Book; every SafeC program elsewhere on this site that the playground can build (one that includes only the C and std headers bundled with its compiler, below) has a Run in Playground link that opens it here.
Share puts the program into the page's address (#code=…, base64url) and copies the link — nothing is uploaded anywhere.
Run compiles and runs the program entirely in your browser, in a background worker, with a self-hosted SafeC compiler built to WebAssembly. Programs see a printf/stdout but no files, network or threads. The compiler is scc, SafeC's compiler written in SafeC (selfhost/); it accepts the language subset described in its SUBSET.md and does not run the ownership and thread-safety checks. Programs can include the C library subsets stdio.h, stdlib.h, string.h, ctype.h, math.h, stdbool.h, stdint.h, stddef.h, limits.h, time.h and assert.h, and the std headers std/io.h, std/str.h, std/mem.h, std/fmt.h, std/math.h, std/convert.h, std/panic.h, std/result.h, std/cmp.h, std/traits.h, std/bit.h, std/atomic.h, std/sys.h, std/time.h (UTC only: there is no time zone, and the clock reads the epoch), std/collections/{slice,vec,string,map}.h and the small headers they use.
What scc leaves out: inline asm and bitfields are rejected; SIMD vector types, _Generic, thread_local, the atomic built-ins, calling-convention keywords, naked, section, interrupt and malloc_defer aren't implemented; a program is one translation unit. spawn runs the thread function to completion at once (there are no threads), and pointers are 4 bytes (wasm32), so sizeof of a type holding pointers differs from a 64-bit native build.

For the checks scc skips, and for the full std, run programs locally:

bash

safeguard new hello && cd hello
# paste the program into src/main.sc
safeguard run

About the playground #

About the playground