C# using PInvoke to call an unmanaged DLL

-
Recently I've found myself having to do some pinvoking with .net. Microsoft offers an excellent primer on the subject.

http://msdn.microsoft.com/en-us/library/aa288468(v=vs.71).aspx

For it's many great benefits the .net framework doesn't do everything. You will find yourself having to invoke a win32 API function call at some point in your career.


I'm going to offer some quick and dirty samples on getting data back and forth using the platform invoke. First you cannot invoke any classes using pinvoke. You get 1 function call at a time. If you want classes you will need to write a custom CLI/C++ wrapper. But that goes beyond the scope of this post.

First let's look at the unmanaged\win32 side of things. Let's say you have a dll called MyDll.dll. In this dll you have a bunch of functions.

// this lets use export functions from the dll
#define  DllExport  __declspec( dllexport ) 

// first we use extern "C" so we don't get name mangling in the dll
// .net doesn't play well with C++ function names so we must use the extern
extern "C"
{    
    // we're going to export this function using the __stdcall calling convention
    // .net uses __stdcall by default, so we want to ensure we have it here
    DllExport int __stdcall Add( int A, int B )
    {
        return A + B;
    }
}


So a quick re-cap, we're going to export a single function called Add, using the __stdcall calling convention. Now let's look at using this function in a .net application. The trick is to use the DllImport attribute, located in the System.Runtime.InteropServices namespace. Below is an example of using the DllImport to use our Add method.

[DllImport( "MyDll.dll" )]
public static extern int Add( int A, int B );

// call our add method!
int result = Add( 1, 2 );

.Net is actually very good at matching the basic data types (int, long, bool, etc). Strings, delegates, classes, structs, etc require more work to function correctly. For those we will start getting into more manual marshaling of data. I have found for most basic dll calls letting the framework handle the marshaling saves a lot of time.

Comments

Post a Comment

Popular posts from this blog

String.Replace vs Regex.Replace

-
Image
I recently ran into a situation where I had to do some string manipulation. I had to replace some bad text with valid text. All this had to do with creating valid xml element names. So we had to string white space and some other invalid characters and replace them with valid xml element formatting. To do this we ended up using the Regex.Replace static method. Simply because there was some complexity involved that would have entailed using more then 1 String.Replace call when we can do it all with one regular expression. This caused some discussion about how heavy the regex class is and when to use it. I decided to do some testing and these are my results. First the code static void Main( string[] args ) { // this is our test value string testValue = "This is a test string"; int count; // run the regex replace DateTime regexStart = DateTime.Now; for( count = 0; count < 10000000; count++ ) { string newValue = Regex.Replace( testValue, &qu
Read more

C# Form Application in Kiosk Mode/Fullscreen

-
Sometimes you need to have a C# windows form application run in full screen mode.  Like you see on a kiosk at a mall or some stand alone machine.  It's fairly easy you just need to set some of the properties on the Form either in it's OnLoad method or directly in the designer. In the OnLoad method of the main Form set these values, or again set them directly in the designer. this.MaximizeBox = false; this.TopMost = true; this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None; this.WindowState = System.Windows.Forms.FormWindowState.Maximized;
Read more

Javascript numeric only text box

-
So working on an asp.net page I found I needed a numeric only text box that allowed numbers from 0-100 with no decimals. I found a range validator would do most of the work but I wanted to keep users from typing in bad values. So after some searching I found javascript has a good solution. I like whitespace so shrink if you're one of those white space freaks. Update: someone was kind enough to point out an error in my JS! So I went through and made sure it works. And it did need a minor tweak to be correct. So thanks to the poster the corrected script and usage are below. Update Again: This is the new and improved function to allow for the tab key to tab out of the text box. IE allows this by default however Firefox really tightens down the text box and doesn't allow anything you don't specify. So I had to add the tab key press. I also cleaned up the code so it isn't a huge chunk of if blocks and is now much more succinct. Please feel free to test and us
Read more