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Dynamic Invoke from Unmanaged DLL

, 4 Jan 2005
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This article explains invoking unmanaged DLL functions from C#.


This article demonstrates how to call an unmanaged MFC DLL function from a C# code. Code uses Reflection namespace. To use code snippets below, you must add the following:

using System.Reflection.Emit;
using System.Reflection;

Imagine you have an MFC DLL (getmyversion.dll) with function named int GetDllversion(char* verstr) which returns your DLL's version in verstr.

The below function creates a dynamic assembly object. And DefinePInvokeMethod method creates a method which we will use to access our DLL function. To complete our global ops for our dynamic module, call CreateGlobalFunctions. Using GetMethod function of our previously created method, we can invoke our MFC DLL function.

public  object DynamicDllFunctionInvoke( string DllPath, string EntryPoint ) 
   // Version string definition
   byte[] verstr = new byte[1024];
   //Define return type of your dll function.
   Type returnType = typeof(int);        
   //out or in parameters of your function.   
   Type [] parameterTypes = {typeof(byte[])};
   object[] parameterValues = {verstr};
   string entryPoint = entrypoint;
   // Create a dynamic assembly and a dynamic module
   AssemblyName asmName = new AssemblyName();
   asmName.Name = "tempDll";
   AssemblyBuilder dynamicAsm = 
   ModuleBuilder dynamicMod = 

   // Dynamically construct a global PInvoke signature 
   // using the input information
   MethodBuilder dynamicMethod = dynamicMod.DefinePInvokeMethod(
     entryPoint, DllPath, MethodAttributes.Static | MethodAttributes.Public
     | MethodAttributes.PinvokeImpl , CallingConventions.Standard,
     returnType, parameterTypes, CallingConvention.Winapi, 

   // This global method is now complete

   // Get a MethodInfo for the PInvoke method
   MethodInfo mi = dynamicMod.GetMethod(EntryPoint);
   // Invoke the static method and return whatever it returns
   object retval = mi.Invoke(null, parameterValues);
   // Filled verstr paramter.
   return retval;

Sample calling of the method is as below:



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Comments and Discussions

GeneralMy vote of 1 Pinmembermerikin28-Jun-10 5:14 
Questionreal dynamic invoke [modified] Pinmemberfredarmoni21-Aug-07 1:10 
AnswerRe: real dynamic inoke PinmemberShawn-USA5-Aug-13 16:21 
QuestionHow to Unload a DLL PinmemberRonakkumar Patel31-May-07 14:21 
AnswerRe: How to Unload a DLL PinmemberShawn-USA5-Aug-13 16:24 
Questionwhen load dll of vc++6.0 its generated error?? Pinmemberkeyur_patel26-Mar-07 22:57 
AnswerRe: when load dll of vc++6.0 its generated error?? Pinmembercalaquendi26-Mar-07 23:34 
QuestionReturned value does not work Pinmembermczard31-May-06 1:10 
I have tried the code. I am able to call a DLL function, arguments are passed properly, but I cannot get the returned value. When working with int-returing functions I get always 0, when working with strings I get always null. I have tried the DLL in the static way (DllImport attribute] and it works. Can somebody help me?
BTW. I found another solution of this problem here:
but it has one limitation - name of the function to call must be known at compile-time.
Generalref string PinmemberJohn Orosz17-Mar-05 7:34 
QuestionRe: ref string Pinmembernpat19-Jan-07 12:11 
AnswerRe: ref string PinmemberJorge Branco29-Aug-08 11:28 
GeneralRe: ref string PinmemberJorge Branco29-Aug-08 11:39 
QuestionDllImport Attribute? PinprotectorMarc Clifton4-Jan-05 6:25 
AnswerRe: DllImport Attribute? PinmemberChris Richardson4-Jan-05 11:40 
GeneralRe: DllImport Attribute? PinprotectorMarc Clifton4-Jan-05 11:56 
GeneralRe: DllImport Attribute? PinmemberChris Richardson4-Jan-05 12:06 
AnswerRe: DllImport Attribute? Pinmembercalaquendi4-Jan-05 21:09 
AnswerRe: DllImport Attribute? PinmemberHarkos5-Jan-05 1:20 
GeneralRe: DllImport Attribute? PinsussSuperfan25-Jan-05 16:01 
GeneralRe: DllImport Attribute? PinmemberHarkos26-Jan-05 0:23 
GeneralRe: DllImport Attribute? PinsussSuperfan26-Jan-05 6:34 

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