$ cat hello.txt
hello
$ cat a.zig
const io = @import("std").io;
const mem = @import("std").mem;
const assert = @import("std").debug.assert;
const heap = @import("std").heap;
pub fn main() -> %void {
    var f = %return io.File.openRead("hello.txt", &heap.c_allocator);
    const in = &f.in_stream;
    const buf = %return in.readAllAlloc(&heap.c_allocator, 100);
    assert(mem.eql(u8, buf, "hello\n"));
}
$ zig build-exe --library c a.zig
$ ./a && echo $?
0