_Format _Unit _Value Ampere AngMinute AngSecond Bar Calorie Candela CentiMetre Coulomb CubicFoot DeciMetre Degree ElectronVolt Farad Foot Gauss getFormat getUnit getUserString getUserString getUserString getValue getValueAs GigaHertz GigaPascal Gon Gram Henry Hertz Hour Hundredweights Inch isDimensionless isQuantity isValid Joule Kelvin KiloAmpere KiloCalorie KiloElectronVolt KiloGram KiloHertz KiloJoule KiloMetre KiloNewton KiloNewtonPerMeter KiloOhm KiloPascal KiloSiemens KiloVolt KiloWatt KiloWattHour KMH KSI Liter MegaAmpere MegaElectronVolt MegaHertz MegaNewton MegaNewtonPerMeter MegaOhm MegaPascal MegaSiemens Metre MicroFarad MicroGram MicroHenry MicroKelvin MicroMetre MicroSiemens Mile MilePerHour MilliAmpere MilliBar MilliFarad MilliGram MilliHenry MilliJoule MilliKelvin MilliLiter MilliMetre MilliMole MilliNewton MilliNewtonPerMeter MilliSiemens MilliVolt MilliWatt Minute Mole MPH MPSI mTorr NanoFarad NanoHenry NanoMetre Newton NewtonMeter NewtonPerMeter Oersted Ohm operator* operator* operator+ operator+= operator- operator- operator-= operator/ operator/ operator< operator<= operator= operator== operator> operator>= Ounce parse Pascal PicoFarad Pound PoundForce pow pow PSI Quantity Quantity Quantity Quantity Radian Second setFormat setInvalid setUnit setValue Siemens SquareFoot Stone TeraHertz Tesla Thou Ton Torr Volt VoltAmpere VoltAmpereSecond Watt WattSecond Weber Yard yTorr ~Quantity

isValid() bool isValid ( ) const 检查是否为有效值 检查当前 Quantity 对象是否为有效值（即有数值，无论是否有单位）。 返回 如果有效，返回 true；否则返回 false