ArcSDE C API在.NET中的调用

using System.Runtime.InteropServices;
[DllImport("sde.dll")]//还有其他的属性可参考MSDN
public static extern Int32 SE_connection_create(string server, string instance, string database, string username, string pwd, ref SE_ERROR error, out IntPtr pSdeConn);
'--------------↓声明SE_ERROR结构体↓-----------------

<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Unicode)> _
Public Structure SE_ERROR
Public sde_error As Int32
Public ext_error As Int32
'<MarshalAs(UnmanagedType.ByValArray, SizeConst:=512)> _
            Public err_msg1 As Char()
'<MarshalAs(UnmanagedType.ByValArray, SizeConst:=4096)> _
            Public err_msg2 As Char()
End Structure
'--------------↑声明SE_ERROR结构体↑-----------------

'-------------------调用SE_connection_create函数----------------------
        '------------------连接SDE-------------------------
        '返回结果
        'SE_SUCCESS     0
        'SE_FAILURE     -1
        'SE_NO_ACCESS   -15
        'SE_SDE_NOT_STARTED     -5
        'SE_IOMGR_NOT_AVAILABLE     -101
        'SE_INVALID_DATABASE        -162
        'SE_INVALID_SERVER      -100
        'SE_INVALID_POINTER     -65
        'SE_INVALID_USER        -9
        'SE_LOGIN_NOT_ALLOWED       -8
        'SE_DBMS_DOES_NOT_SUPPORT       -1008
        'SE_NET_FAILURE     -10
        'SE_NET_TIMEOUT     -11
        'SE_SERVICE_NOT_FOUND       -102
        'SE_TASKS_EXCEEDED      -7

<DllImport("sde.dll", SetLastError:=True,ThrowOnUnmappableChar:=True)> _
Public Shared Function SE_connection_create(ByVal server As String, ByVal instance As String, _
ByVal database As String, ByVal username As String, ByVal password As String, ByRef error1 As SE_ERROR, _
ByRef connection As IntPtr) As Int32
End Function
'----------------------------调用SE_connection_free函数-------------------------
        '----------------------------释放SDE连接----------------------
        <DllImport("sde.dll", SetLastError:=True, ThrowOnUnmappableChar:=True)> _
Public Shared Sub SE_connection_free(ByVal Byrefconnection As IntPtr)
End Sub

Imports QHProject.SDE_C_API
Imports System.Runtime.InteropServices
Partial Class MapServicePage
Inherits System.Web.UI.Page
Private Shared conn As IntPtr = Nothing
Private error1 As QHProject.SDE_C_API.SDE_C_API_Operation.SE_ERROR = Nothing
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
End Sub
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim i As Int32 = SDE_C_API_Operation.SE_connection_create("CL", "5151", "sde", "sde", "clbeyond", error1, conn)
Button1.Text = i.ToString()
End Sub
Protected Sub Button2_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button2.Click
SDE_C_API_Operation.SE_connection_free(conn)
End Sub
End Class
  连接成功后Button的Text属性会显示为0，表示连接成功，在任务管理器中就会发现出现了一个gsrvr.ext进程。断开连接后gsrvr.exe进程就会消失。
  当然前提是要在程序中将连接字段conn声明为shared类型（C#中的Static类型）。
  需要注意的是Instance不是"esri_sde"，而是端口号，一般为5151。