我的编译会出现D:\arduino-1.5.2-windows\arduino-1.5.2\libraries\nrf24l01\Multiple.cpp: In member function 'int Multiple::set_reg(String, String)':
D:\arduino-1.5.2-windows\arduino-1.5.2\libraries\nrf24l01\Multiple.cpp:268: error: 'class String' has no member named 'c_str',请问要怎么处理