Function FLSlice_ToCString 

pub unsafe extern "C" fn FLSlice_ToCString(
    s: FLSlice,
    buffer: *mut c_char,
    capacity: usize,
) -> bool

Copies a slice to a buffer, adding a trailing zero byte to make it a valid C string. If there is not enough capacity the slice will be truncated, but the trailing zero byte is always written. @param s The FLSlice to copy. @param buffer Where to copy the bytes. At least capacity bytes must be available. @param capacity The maximum number of bytes to copy (including the trailing 0.) @return True if the entire slice was copied, false if it was truncated.