Function mmal_sys::vcos_safe_vsprintf

pub unsafe extern "C" fn vcos_safe_vsprintf(
    buf: *mut c_char, 
    buflen: usize, 
    offset: usize, 
    fmt: *const c_char, 
    ap: va_list
) -> usize

Like vsnprintf, except it places the output at the specified offset. Output is truncated to fit in buflen bytes, and is guaranteed to be NUL-terminated. Returns the string length before/without truncation.