C# 利用P/Invoke调用PMAC的Pcomm32.dll， 函数字符串返回值为空

[beihanggl]

大家帮我看看，这是利用P/Invoke委托连接PComm32.dll动态连接库，向一个PMAC设备发送指令的语句，向下发送能够成功，但返回值应该在buf值，但就是没有怎么回事？字符串buf为空，急等调试，谢谢各位高手，在线等
PMAC的PComm32.dll中函数原形为：long PMACGETRESPONSEA(DWORD dwDevice,PCHAR response,UINT maxchar,PCHAR command)

C#代码如下
namespace aaa
{
public delegate Int32 Delegate_GetResponsePmac(UInt32 dwDevice, string response, UInt32 maxchar, string command);//20080713

public class bbb: Form
{
dld test1 = new dld();
Delegate_GetResponsePmac GetResponsePmac;

private bbb_load
{
test1.LoadDll("PComm32.dll");
IntPtr GetResponsePmacAddress = test1.LoadFun("PmacGetResponseA");
GetResponsePmac = Marshal.GetDelegateForFunctionPointer(GetResponsePmacAddress, typeof(Delegate_GetResponsePmac)) as
}

private void button_click(object sender, EventArgs e)
{

string buf = "";
Int32 temp = GetResponsePmac(0, buf, 10, comboBox_Command.Text.ToString());
}
}
}

[珍惜生命远离CPP]

指定字符集为Ansi

[beihanggl]

还在吗？您能不能在详细讲一下，我是默认的charset，不是说默认情况下就是ansi字符吗？谢谢您了

[beihanggl]

我在通信类dld中进行了字符集类型强行指定，可还是不行，大家帮帮我吧
class dld
{
[DllImport("kernel32.dll",CharSet=CharSet.Ansi)]
internal static extern IntPtr LoadLibrary(string lpFileName);
[DllImport("kernel32.dll",CharSet=CharSet.Ansi)]
internal static extern IntPtr GetProcAddress(IntPtr hModule, string lpProcName);
[DllImport("kernel32.dll",CharSet=CharSet.Ansi)]
public static extern bool FreeLibrary(IntPtr hModule);
}