这是C++的代码
CRYPTOAPI_API short CALLBACK Encrypt(LPTSTR sOrigin,LPTSTR sEncrypt) 
{ 
  int    i; 
  char *sSource,*sConvert; 

   if (sOrigin !=  NULL) { 
    sSource =  new char[strlen(sOrigin)+21]; 
    sConvert =  new char[strlen(sOrigin)+21]; 
    strcpy(sSource,sOrigin); 

    Confuse(sSource,sConvert); 
    strcpy(sSource,sConvert); 
    Explode(sSource,sConvert); 
     for (i=0;i<10;i++) { 
      Shuffle(sConvert); 
    } 
    strcpy(sEncrypt,sConvert); 
    delete sConvert; 
    delete sSource; 
  } 
   else { 
    strcpy(sEncrypt,""); 
  } 
  return 1; 
} 
现在我要在C#中调用 CryptoAPI.dll中的Encrypt函数，首先我把dll拷贝到bin下。
using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Runtime.InteropServices; 
namespace ConsoleApplication1 
{ 
         class Program 
        { 
                 static  void Main( string[] args) 
                { 
                        StringBuilder sb =  new StringBuilder(); 
                        StringBuilder sb1 =  new StringBuilder(); 
                        StringBuilder sb2 =  new StringBuilder(); 
                        sb.Append( "000000"); 
                        String ss = ""; 
                        test.Encrypt(sb, sb1); 
                        test.Decrypt(sb1, sb2); 
                        Console.ReadLine(); 
                } 
        } 
         class test 
        { 
                [DllImport( "CryptoAPI.dll", EntryPoint =  "Encrypt", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)] 
                 public  static  extern  short Encrypt(StringBuilder str, StringBuilder str1); //实现DLL加密 
                [DllImport( "CryptoAPI.dll", EntryPoint =  "Decrypt", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.StdCall)] 
                 public  static  extern  short Decrypt(StringBuilder str1, StringBuilder str2); //实现DLL解密 
        } 
} 
只要你的函数返回类型和参数跟C++的对应上即可。LPTSTR对应C#的StringBuilder。Char **对应C#的ref string，具体的用到了再去查。还有C++的编码一定要和C#的编一致.接下来我再介绍下非托管DLL的动态调用
using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; 
using System.Runtime.InteropServices; 
 
namespace ConsoleApplication1 
{ 
         public  class DLLWrapper 
        { 
                 ///<summary>    
                 ///API LoadLibrary    
                 ///</summary>    
                [DllImport( "Kernel32")] 
                 public  static  extern  int LoadLibrary(String funcname); 
 
                 ///<summary>    
                 ///API GetProcAddress    
                 ///</summary>    
                [DllImport( "Kernel32")] 
                 public  static  extern  int GetProcAddress( int handle, String funcname); 
                 ///<summary>    
                 ///API FreeLibrary    
                 ///</summary>    
                [DllImport( "Kernel32")] 
                 public  static  extern  int FreeLibrary( int handle); 
                 ///<summary>    
                 ///通过非托管函数名转换为对应的委托
                 ///</summary>    
                 ///<param name="dllModule">通过LoadLibrary获得的DLL句柄</param>    
                 ///<param name="functionName">非托管函数名</param>    
                 ///<param name="t">对应的委托类型</param>    
                 ///<returns>委托实例，可强制转换为适当的委托类型</returns>    
                 public  static Delegate GetFunctionAddress( int dllModule,  string functionName, Type t) 
                { 
                         int address = GetProcAddress(dllModule, functionName); 
                         if (address == 0) 
                                 return  null; 
                         else 
                                 return Marshal.GetDelegateForFunctionPointer( new IntPtr(address), t); 
                } 
 
                 ///<summary>    
                 ///将表示函数地址的IntPtr实例转换成对应的委托                  ///</summary>    
                 public  static Delegate GetDelegateFromIntPtr(IntPtr address, Type t) 
                { 
                         if (address == IntPtr.Zero) 
                                 return  null; 
                         else 
                                 return Marshal.GetDelegateForFunctionPointer(address, t); 
                } 
 
                 ///<summary>    
                 ///将表示函数地址的int转换成对应的委托
                 ///</summary>    
                 public  static Delegate GetDelegateFromIntPtr( int address, Type t) 
                { 
                         if (address == 0) 
                                 return  null; 
                         else 
                                 return Marshal.GetDelegateForFunctionPointer( new IntPtr(address), t); 
                } 
 
                 delegate  short Encrypt(StringBuilder decrypt, StringBuilder encrypt); 
 
                 public  string ReadDLL() 
                { 
                         int hModule = DLLWrapper.LoadLibrary( "CryptoAPI.dll"); 
                         if (hModule == 0) 
                                 return  "0"; 
                        Encrypt encrypt = (Encrypt)DLLWrapper.GetFunctionAddress(hModule,  "Encrypt",  typeof(Encrypt)); 
                         if (encrypt ==  null) 
                        { 
                                DLLWrapper.FreeLibrary(hModule); 
                                 return  "0"; 
                        } 
                        StringBuilder ss =  new StringBuilder(100); 
                        StringBuilder sb =  new StringBuilder(100); 
                        sb.Append( "aaa"); 
                        encrypt(sb, ss); 
                        DLLWrapper.FreeLibrary(hModule); 
                         return ss.ToString(); 
                } 
        } 
}