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Dynamic Invoke from Unmanaged DLL

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4 Jan 2005 91.1K   31   21
This article explains invoking unmanaged DLL functions from C#.

Introduction

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:

C#
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.

C#
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 = 
     AppDomain.CurrentDomain.DefineDynamicAssembly(asmName, 
     AssemblyBuilderAccess.Run);
   ModuleBuilder dynamicMod = 
     dynamicAsm.DefineDynamicModule("tempModule");

   // 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, 
     CharSet.Ansi);

   // This global method is now complete
   dynamicMod.CreateGlobalFunctions();

   // 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.
   MessageBox.Show(System.Text.ASCIIEncoding.ASCII.GetString(verstr));
   return retval;
  }

Sample calling of the method is as below:

C#
DynamicDllFunctionInvoke(@"c:\getmyversion.dll","GetDllVersion");

License

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Comments and Discussions

 
GeneralMy vote of 1 Pin
merikin28-Jun-10 5:14
merikin28-Jun-10 5:14 
Questionreal dynamic invoke Pin
fredarmoni21-Aug-07 1:10
fredarmoni21-Aug-07 1:10 
AnswerRe: real dynamic inoke Pin
Shawn-USA5-Aug-13 16:21
Shawn-USA5-Aug-13 16:21 
For a C-style DLL, it can export function names and ordinal number. So you won't be able to know the parameter type and number of parameters. You can if you have the header file of the DLL.

For a C++ DLL, you will be able to know the names, parameter types, and number of parameter types by demangle the mangled C++ function names without using the header files, but you will have to reply on the heaer files to calculate the size of the instance of classes. Otherwise, you will have to make a guess about the size, maybe just make it a big number.

With either DLL, once you have all the information I mentioned, you will surely be able to declare and use the functions from the DLL by using dynamic methods.

QuestionHow to Unload a DLL Pin
Ronakkumar Patel31-May-07 14:21
Ronakkumar Patel31-May-07 14:21 
AnswerRe: How to Unload a DLL Pin
Shawn-USA5-Aug-13 16:24
Shawn-USA5-Aug-13 16:24 
Questionwhen load dll of vc++6.0 its generated error?? Pin
keyur_patel26-Mar-07 22:57
keyur_patel26-Mar-07 22:57 
AnswerRe: when load dll of vc++6.0 its generated error?? Pin
calaquendi26-Mar-07 23:34
calaquendi26-Mar-07 23:34 
QuestionReturned value does not work Pin
Michal Czardybon31-May-06 1:10
Michal Czardybon31-May-06 1:10 
Generalref string Pin
John Orosz17-Mar-05 7:34
John Orosz17-Mar-05 7:34 
QuestionRe: ref string Pin
npat19-Jan-07 12:11
npat19-Jan-07 12:11 
AnswerRe: ref string Pin
Jorge Branco29-Aug-08 11:28
Jorge Branco29-Aug-08 11:28 
GeneralRe: ref string Pin
Jorge Branco29-Aug-08 11:39
Jorge Branco29-Aug-08 11:39 
QuestionDllImport Attribute? Pin
Marc Clifton4-Jan-05 6:25
mvaMarc Clifton4-Jan-05 6:25 
AnswerRe: DllImport Attribute? Pin
Chris Richardson4-Jan-05 11:40
Chris Richardson4-Jan-05 11:40 
GeneralRe: DllImport Attribute? Pin
Marc Clifton4-Jan-05 11:56
mvaMarc Clifton4-Jan-05 11:56 
GeneralRe: DllImport Attribute? Pin
Chris Richardson4-Jan-05 12:06
Chris Richardson4-Jan-05 12:06 
AnswerRe: DllImport Attribute? Pin
calaquendi4-Jan-05 21:09
calaquendi4-Jan-05 21:09 
AnswerRe: DllImport Attribute? Pin
Leonardo Pessoa5-Jan-05 1:20
Leonardo Pessoa5-Jan-05 1:20 
GeneralRe: DllImport Attribute? Pin
Superfan25-Jan-05 16:01
Superfan25-Jan-05 16:01 
GeneralRe: DllImport Attribute? Pin
Leonardo Pessoa26-Jan-05 0:23
Leonardo Pessoa26-Jan-05 0:23 
GeneralRe: DllImport Attribute? Pin
Superfan26-Jan-05 6:34
Superfan26-Jan-05 6:34 

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