在snapi.h里面有定义:
////////////////////////////////////////////////////////////////////////////////
// PhoneSignalStrength
// Get the phone signal strength, expressed as a percentage of full strength.
#define SN_PHONESIGNALSTRENGTH_ROOT HKEY_LOCAL_MACHINE
#define SN_PHONESIGNALSTRENGTH_PATH TEXT("System\\State\\Phone")
#define SN_PHONESIGNALSTRENGTH_VALUE TEXT("Signal Strength Raw")