在C#中使用EHLLAPI从IBM iSeries获取字符串将得到字符串，后面是垃圾信息

Question

我正试图在as400模拟器(ISeries iSeries)中自动化一个进程，为此，我使用了一些使用EHLLAPI连接到模拟器的代码(我完全不是从CodeProject窃取的)。

我创建了一个Winforms来实现代码，使用一些按钮和一些文本框来测试它。下面是从EHLLAPI公开方法的类：

public class EhllapiFunc //Class used to import the DLL.
{
    [DllImport("PCSHLL32.dll")]
    public static extern UInt32 hllapi(out UInt32 Func, StringBuilder Data, out UInt32 Length, out UInt32 RetC);
}

class EhllapiWrapper
{
    /*These are the constants used to as function codes that are sent as parameters to the function in the DLL. 
    There are a lot more constants but these are the only ones used for the moment*/
    const UInt32 HA_CONNECT_PS = 1; /* 000 Connect PS*/
    const UInt32 HA_DISCONNECT_PS = 2; /* 000 Disconnect PS*/
    const UInt32 HA_COPY_PS_TO_STR = 8; /* 000 Copy PS to String*/
    
    /*EHLLAPI return codes. There are a lot more. I'll leave just some of them as I'm not getting any return codes in my issue*/
    const UInt32
        HARC_SUCCESS = 0; /* 000 Good return code.*/
    const UInt32
        HARC99_INVALID_INP = 0; /* 000 Incorrect input*/
    const UInt32
        HARC_INVALID_PS = 1; /* 000 Invalid PS, Not*/
    const UInt32
        HARC_BAD_PARM = 2; /* 000 Bad parameter, or*/
    
    //Method to connect to the emulator.
    public static UInt32 Connect(string sessionID)
    {
        StringBuilder Data = new StringBuilder(4);
        Data.Append(sessionID);
        UInt32 rc = 0;
        UInt32 f = HA_CONNECT_PS;
        UInt32 l = 4;
        return EhllapiFunc.hllapi(out f, Data, out l, out rc);
    }

    //Method to disconnect.
    public static UInt32 Disconnect(string sessionID)
    {
        StringBuilder Data = new StringBuilder(4);
        Data.Append(sessionID);
        UInt32 rc = 0;
        UInt32 f = HA_DISCONNECT_PS;
        UInt32 l = 4;
        return EhllapiFunc.hllapi(out f, Data, out l, out rc);
    }

    /*This is the method where I'm having the problem.*/
    public static UInt32 ReadScreen(int position, int len, out string txt)
    {
        StringBuilder Data = new StringBuilder(3000);
        UInt32 rc = (UInt32)position;
        UInt32 f = HA_COPY_PS_TO_STR;
        UInt32 l = (UInt32)len;
        UInt32 r = EhllapiFunc.hllapi(out f, Data, out l, out rc);
        txt = Data.ToString();
        return r;
    }
}

这是我用来调用表单上的方法的OnClick事件：

private void bReadString_Click(object sender, EventArgs e)
{
    //I tried cleaning the TextBox where the outputed string is sent before calling the method.
    tbReadOut.Text = "";
    string s;
    //I send the position and string length entered on the form to the method and then "s" is modified inside the method "ReadScreen".
    EhllapiWrapper.ReadScreen(Convert.ToInt32(tbReadPos.Text), Convert.ToInt32(tbReadLen.Text), out s);
    tbReadOut.Text = s;
}

下面是这个问题的一个例子。我应该从光标位置“30”得到一个2个字符大小的字符串：

我得到的垃圾信息是"String Result“

​

这是我应该从模拟器中得到的区域，只需要"Sy"：

​

我尝试了模拟器的不同部分，发现问题是一样的。获取光标位置并发送字符串工作得很好，这只是在我试图从仿真器获取字符串时。

我甚至不知道去哪里寻找答案，因为这段代码最初是在2005年发布的。

Answer 1

我找到问题了。在ReadScreen方法中，我创建了一个需要3000个字符的StringBuilder。当我在该方法的参数中使用out时，我处理的是一个内存地址，而不仅仅是两个变量。当我为至少3000个字符分配空间时，当我读取的字符串很小时，有时它会带有来自“未使用”空间的垃圾。我所做的是将StringBuilder的预期大小更改为我试图读取的字符串的长度减去1(如果只是这个长度，我仍然会得到一个垃圾字符)。代码如下：

public static UInt32 ReadScreen(int position, int len, out string txt)
{
    StringBuilder Data = new StringBuilder(len - 1); //This line was the problem.
    UInt32 rc = (UInt32)position;
    UInt32 f = HA_COPY_PS_TO_STR;
    UInt32 l = (UInt32)len;
    UInt32 r = EhllapiFunc.hllapi(out f, Data, out l, out rc);
    txt = Data.ToString();
    return r;
}

我的解释可能是错误的，因为我还在学习C#，代码最初是2005年的，但这个修改对我来说是有效的。如果我误解了什么或者我做错了什么，请随时纠正我。