def get_c_declarations(header_filename):
    """
    Extracts C declarations important for the cFFI module from the SimpLL FFI
    header file.
    :param filename Name of the SimpLL header file
    """
    cdef_start = "// CFFI_DECLARATIONS_START\n"
    cdef_end = "// CFFI_DECLARATIONS_END\n"

    with open(header_filename, "r") as header_file:
        lines = header_file.readlines()
        start = lines.index(cdef_start) + 1
        end = lines.index(cdef_end)
        return "".join(lines[start:end])