pinvoke.net: Edit: kernel32.GetPRocAddress

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Summary: The GetProcAddress API

!!!!C# Signature:
 [DllImport("kernel32", CharSet=CharSet.Ansi, ExactSpelling=true, SetLastError=true)]
 static extern IntPtr GetProcAddress(IntPtr hModule, string procName);

!!!!VB.NET Signature:
 <DllImport("kernel32.dll", SetLastError:=True, CharSet:=CharSet.Ansi, ExactSpelling:=True)> _
 Private Function GetProcAddress(ByVal hModule As IntPtr, ByVal procName As String) As UIntPtr
 End Function

!!!!VB Signature:
 Private Declare Function GetProcAddress Lib "kernel32" (ByVal hModule As Integer, ByVal lpProcName As String) As Integer

!!!!C++ Signature:
 [DllImport("KERNEL32.DLL", CharSet=CharSet::Ansi, EntryPoint="GetProcAddress", ExactSpelling=true)]
 static IntPtr GetProcAddress(IntPtr hModule, String^ lpProcName);

!!!!Boo Signature:
 [DllImport("kernel32.dll", CharSet : CharSet.Ansi, ExactSpelling : true)]
 static def GetProcAddress(hModule as IntPtr, procName as string) as IntPtr:
     pass
!!!!User-Defined Types:
None.

!!!!Notes:
GetProcAddress only comes in an ANSI flavor, hence we help the runtime by telling it to always use ANSI when marshalling the string parameter.  We also prevent the runtime looking for a non-existent ''GetProcAddressA'', because the default for C# is to set ''ExactSpelling'' to false.

!!!!Tips & Tricks:
This API becomes a lot more interesting in .NET v2.0 because the System.Runtime.InteropServices.Marshal class gains a new API called GetDelegateForFunctionPointer(). This means that you will be able to write code like this:

internal static class UnsafeNativeMethods {
   [DllImport("kernel32", CharSet=CharSet.Ansi, ExactSpelling=true, SetLastError=true)]
   internal static extern IntPtr GetProcAddress(IntPtr hModule, string procName );
 }

internal delegate int DllRegisterServerInvoker();

// code snippet in a method somewhere, error checking omitted
 IntPtr fptr = UnsafeNativeMethods.GetProcAddress( hModule, "DllRegisterServer" );
 DllRegisterServerInvoker drs = (DllRegisterServerInvoker) Marshal.GetDelegateForFunctionPointer( fptr, typeof(DllRegisterServerInvoker) );
 drs(); // call via a function pointer

Some DLLs only export by ordinal.  Because you can't express this mode of GetProcAddress to the marshaller, one possibility is to import the function a second time with another name, such as:

[DllImport("kernel32", SetLastError = true, EntryPoint = "GetProcAddress")]
 static extern IntPtr GetProcAddressOrdinal(IntPtr hModule, IntPtr procName);

!!!!Sample Code:
for load function "Test" from DLL "MyDLL.dll" we do this codes:
 static HMODULE hDLL;
 typedef HRESULT (STDAPICALLTYPE * LPFNTEST) (void);
 LPFNTEST _pfnTest;
 
 hDLL = LoadLibrary("MyDLL.dll");
 _pfnTest = (LPFNTEST)::GetProcAddress(hDLL, "Test");

!!!!Alternative Managed API:
Do you know one?  Please contribute it!

Documentation: GetProcAddress@msdn on MSDN