Function CSTL_string_c_str 

pub unsafe extern "C" fn CSTL_string_c_str(
    instance: CSTL_StringCRef,
) -> *const c_char

Returns a const pointer to the underlying null-terminated array serving as character storage.

If CSTL_string_empty(instance) == true the pointer is still valid and points to a single null character.

The range [CSTL_string_c_str(instance), CSTL_string_c_str(instance) + size] is always valid.