How to call/access a function/method in unmanaged dll using asp.net/c#

Posted by on May 9, 2010 Leave a comment (0) Go to comments

Introduction:
In this article,i am going to explain about how to call a method in unmanaged dll using System.Runtime.InteropServices.DllImportAttribute option.

Main:
The dllimportattribute method helps to allow the unmanaged dll function utilization.For accessing unmanaged dll function,

*Declare this method as both extern and static, and apply the attribute System.Runtime.InteropServices.DllImportAttribute to specify the DLL file and the name of the unmanaged function.

For examble,i am going to access the win32api functions GetPrivateProfileString and WritePrivateProfileString.These functions are helps us to allow reading and wrinting INI entries,

using System;
using System.Runtime.InteropServices;
using System.Text;
 
namespace Unmanageddll
{
    class UMDllExecution
    {
        // Declare the unmanaged functions.
        [DllImport("kernel32.dll", EntryPoint = "GetPrivateProfileString")]
        private static extern int GetPrivateProfileString(string lpAppName,
          string lpKeyName, string lpDefault, StringBuilder lpReturnedString,
          int nSize, string lpFileName);
        [DllImport("kernel32.dll", EntryPoint = "WritePrivateProfileString")]
        private static extern bool WritePrivateProfileString(string lpAppName,
          string lpKeyName, string lpString, string lpFileName);
 
        static void Main(string[] args)
        {
            string val;
 
            // Obtain current value.
            val = GetIniValue("SampleSection", "Key1", "\\initest.ini");
            Console.WriteLine("Value of Key1 in [SampleSection] is: "
                + val);
 
            // Write a  new value.
            WriteIniValue("SampleSection", "Key1", "New Value",
                "\\initest.ini");
 
            // Obtain the new value.
            val = GetIniValue("SampleSection", "Key1", "\\initest.ini");
            Console.WriteLine("Value of Key1 in [SampleSection] is now: "
                + val);
 
            // Write original value.
            WriteIniValue("SampleSection", "Key1", "Value1",
                "\\initest.ini");
 
            // Wait to continue.
            Console.WriteLine(Environment.NewLine);
            Console.WriteLine("Main method complete. Press Enter.");
            Console.ReadLine();
        }
 
        public static string GetIniValue(string section, string key,
            string filename)
        {
            int chars = 256;
            StringBuilder buffer = new StringBuilder(chars);
            string sDefault = "";
            if (GetPrivateProfileString(section, key, sDefault,
              buffer, chars, filename) != 0)
            {
                return buffer.ToString();
            }
            else
            {
                return null;
            }
        }
 
        public static bool WriteIniValue(string section, string key,
            string value, string filename)
        {
            return WritePrivateProfileString(section, key, value, filename);
        }
    }
}