跪求帮助！调用PCI-Dask.dll，里面有个方法的参数是out关键字，如何调用该方法

跪求帮助！调用PCI-Dask.dll，里面有个方法的参数是out关键字，怎么调用该方法？
[DllImport("PCI-Dask.dll")]
public static extern short DI_ReadPort (ushort CardNumber, ushort Port, out uint Value);

我在C#代码里面调用改方法，
int Result，gIOCard;
long gSigInput;
Result = DASK.DI_ReadPort((ushort)gIOCard, (ushort)0,out (uint) gSigInput）；
一直出现编译错误是：ref或out参数必须是可以赋值的变量！  
跪求大家帮助啊。紧急啊

[解决办法]
ushort Result，gIOCard;
uint gSigInput;
Result = DASK.DI_ReadPort((ushort)gIOCard, 0,out gSigInput）；

试一试
[解决办法]

C# code

// 方法定义[DllImport("PCI-Dask.dll")]public static extern short DI_ReadPort(ushort CardNumber, ushort Port, ref uint Value);// 调用ushort gIOCard = 0;uint gSigInput = 0;short Result = DI_ReadPort(gIOCard, 0, ref gSigInput);