Debugging, Profiling and Hot Reload

42.1 Debugging

println, eprintln, dump(expr), $dbg (built-in REPL-like debugger at a breakpoint, 0.4.6+), @FILE:@LINE, print_backtrace().

Native debuggers: build with -g (maps to V source lines) or -cg (C lines), then gdb ./app, lldb ./app, or VS Code with CodeLLDB.

Inspect generated C: -keepc -showcc or -o out.c.

Sanitizers: v -cc clang -cflags '-fsanitize=address,undefined' -gc none run app.v. Valgrind with -gc none.

v doctor for environment info when filing compiler bugs.

42.2 Profiling

v -profile profile.txt run app.v      # function call counts and times
sort -n -k3 profile.txt | tail
v -prod -cflags -pg app.v             # gprof
perf record ./app && perf report      # Linux perf (build with -g)

42.3 Hot Code Reloading

Great for games and graphics (gg examples support live reloading).

import time

@[live]
fn draw() {
	println('Edit me and save, change applied without restart!')
}

fn main() {
	for {
		draw()
		time.sleep(1 * time.second)
	}
}

v -live run app.v