EntryPointNotFoundException EntryPointNotFoundException EntryPointNotFoundException EntryPointNotFoundException Class

Definition

The exception that is thrown when an attempt to load a class fails due to the absence of an entry method.

public ref class EntryPointNotFoundException : TypeLoadException
[System.Runtime.InteropServices.ComVisible(true)]
public class EntryPointNotFoundException : TypeLoadException
type EntryPointNotFoundException = class
    inherit TypeLoadException
Public Class EntryPointNotFoundException
Inherits TypeLoadException
Inheritance
Attributes

Remarks

An EntryPointNotFoundException exception is thrown when the common language runtime is unable to load an assembly because it cannot identify the assembly's entry point. This exception can be thrown under the following conditions:

  • The common language runtime is unable to locate an application entry point (typically a Main method) in an executable assembly. The application entry point must be a global or static method that has either no parameters or a string array as its only parameter. The entry point can return void, or it can return an Int32 or UInt32 exit code. An application assembly cannot define more than one entry point.

  • The call to a function in a Windows DLL cannot be resolved because the function cannot be found. In the following example, an EntryPointNotFoundException exception is thrown because User32.dll does not include a function named GetMyNumber.

    using System;
    using System.Runtime.InteropServices;
    
    public class Example
    {
       [DllImport("user32.dll")]
       public static extern int GetMyNumber();
       
       public static void Main()
       {
          try {
             int number = GetMyNumber();
          }
          catch (EntryPointNotFoundException e) {
             Console.WriteLine("{0}:\n   {1}", e.GetType().Name,  
                               e.Message);
          } 
       }
    }
    // The example displays the following output:
    //    EntryPointNotFoundException:
    //       Unable to find an entry point named 'GetMyNumber' in DLL 'User32.dll'.
    
    Module Example
    	Declare Auto Function GetMyNumber Lib "User32.dll" () As Integer
    
       Public Sub Main()
          Try
             Dim number As Integer = GetMyNumber()
          Catch e As EntryPointNotFoundException
             Console.WriteLine("{0}:{2}   {1}", e.GetType().Name,  
                               e.Message, vbCrLf)
          End Try   
       End Sub
    End Module
    ' The example displays the following output:
    '    EntryPointNotFoundException:
    '       Unable to find an entry point named 'GetMyNumber' in DLL 'User32.dll'.
    
  • The call to a function in a Windows DLL cannot be resolved because the name used in the method call does not match a name found in the assembly. Frequently, this occurs because the DllImportAttribute.ExactSpelling field is either implicitly or explicitly set to true, the called method includes one or more string parameters and has both an ANSI and a Unicode version, and the name used in the method call does not correspond to the name of this ANSI or Unicode version. The following example provides an illustration by attempting to call the Windows MessageBox function in User32.dll. Because the first method definition specifies CharSet.Unicode for string marshaling, the common language looks for the wide-character version of the function, MessageBoxW, instead of the name used in the method call, MessageBox. The second method definition corrects this problem by calling the MessageBoxW instead of the MessageBox function.

    using System;
    using System.Runtime.InteropServices;
    
    public class Example
    {
       [DllImport("user32.dll", CharSet = CharSet.Unicode, ExactSpelling = true )]
       public static extern int MessageBox(IntPtr hwnd, String text, String caption, uint type);
     
       [DllImport("user32.dll", CharSet = CharSet.Unicode, ExactSpelling = true )]
       public static extern int MessageBoxW(IntPtr hwnd, String text, String caption, uint type);
    
       public static void Main()
       {
          try {
             MessageBox(new IntPtr(0), "Calling the MessageBox Function", "Example", 0);
          }
          catch (EntryPointNotFoundException e) {
             Console.WriteLine("{0}:\n   {1}", e.GetType().Name,  
                               e.Message);
          }
    
          try {
             MessageBoxW(new IntPtr(0), "Calling the MessageBox Function", "Example", 0);
          }
          catch (EntryPointNotFoundException e) {
             Console.WriteLine("{0}:\n   {1}", e.GetType().Name,  
                               e.Message);
          }
       }
    }
    
    Module Example
       Declare Unicode Function MessageBox Lib "User32.dll" Alias "MessageBox" (
          ByVal hWnd As IntPtr, ByVal txt As String, ByVal caption As String, 
          ByVal typ As UInteger) As Integer  
    
       Declare Unicode Function MessageBox2 Lib "User32.dll" Alias "MessageBoxW" (  
          ByVal hWnd As IntPtr, ByVal txt As String, ByVal caption As String, 
          ByVal typ As UInteger) As Integer  
          
       Public Sub Main()
          Try
             MessageBox(IntPtr.Zero, "Calling the MessageBox Function", "Example", 0 )
          Catch e As EntryPointNotFoundException
             Console.WriteLine("{0}:{2}   {1}", e.GetType().Name,  
                               e.Message, vbCrLf)
          End Try
    
          Try
             MessageBox2(IntPtr.Zero, "Calling the MessageBox Function", "Example", 0 )
          Catch e As EntryPointNotFoundException
             Console.WriteLine("{0}:{2}   {1}", e.GetType().Name,  
                               e.Message, vbCrLf)
          End Try
    
       End Sub
    End Module
    
  • You are trying to call a function in a dynamic link library by its simple name rather than its decorated name. Typically, the C++ compiler generates a decorated name for DLL functions. For example, the following C++ code defines a function named Double in a library named TestDll.dll.

    __declspec(dllexport) int Double(int number)
    {
    	return number * 2;
    }
    

    When the code in the following example tries to call the function, an EntryPointNotFoundException exception is thrown because the Double function cannot be found.

    using System;
    using System.Runtime.InteropServices;
    
    public class Example
    {
       [DllImport("TestDll.dll")]
       public static extern int Double(int number);
    
       public static void Main()
       {
          Console.WriteLine(Double(10));
       }
    }
    // The example displays the following output:
    //    Unhandled Exception: System.EntryPointNotFoundException: Unable to find 
    //    an entry point named 'Double' in DLL '.\TestDll.dll'.
    //       at Example.Double(Int32 number)
    //       at Example.Main()
    
    Module Example
       Public Declare Function DoubleNum Lib ".\TestDll.dll" Alias "Double" _
                      (ByVal number As Integer) As Integer
       
       Public Sub Main()
          Console.WriteLine(DoubleNum(10))
       End Sub
    End Module
    ' The example displays the following output:
    '    Unhandled Exception: System.EntryPointNotFoundException: Unable to find an 
    '    entry point named 'Double' in DLL '.\TestDll.dll'.
    '       at Example.Double(Int32 number)
    '       at Example.Main()
    

    However, if the function is called by using its decorated name (in this case, ?Double@@YAHH@Z), the function call succeeds, as the following example shows.

    using System;
    using System.Runtime.InteropServices;
    
    public class Example
    {
       [DllImport("TestDll.dll", EntryPoint = "?Double@@YAHH@Z")]
       public static extern int Double(int number);
    
       public static void Main()
       {
          Console.WriteLine(Double(10));
       }
    }
    // The example displays the following output:
    //    20
    
    Module Example
       Public Declare Function DoubleNum Lib ".\TestDll.dll" Alias "?Double@@YAHH@Z" _
                      (ByVal number As Integer) As Integer
       
       Public Sub Main()
          Console.WriteLine(DoubleNum(10))
       End Sub
    End Module
    ' The example displays the following output:
    '    20 
    

    You can find the decorated names of functions exported by a DLL by using a utility such as Dumpbin.exe.

  • You are attempting to call a method in a managed assembly as if it were an unmanaged dynamic link library. To see this in action, compile the following example to an assembly named StringUtilities.dll.

    using System;
    
    public static class StringUtilities
    {
       public static String SayGoodMorning(String name)
       {
          return String.Format("A top of the morning to you, {0}!", name);
       }
    }
    
    Module StringUtilities
       Public Function SayGoodMorning(name As String) As String
          Return String.Format("A top of the morning to you, {0}!", name)
       End Function
    End Module
    

    Then compile and execute the following example, which attempts to call the StringUtilities.SayGoodMorning method in the StringUtilities.dll dynamic link library as if it were unmanaged code. The result is an EntryPointNotFoundException exception.

    using System;
    using System.Runtime.InteropServices;
    
    public class Example
    {
       [DllImport("StringUtilities.dll", CharSet = CharSet.Unicode )]
       public static extern String SayGoodMorning(String name);
    
       public static void Main()
       {
          Console.WriteLine(SayGoodMorning("Dakota"));
       }
    }
    // The example displays the following output:
    //    Unhandled Exception: System.EntryPointNotFoundException: Unable to find an entry point 
    //    named 'GoodMorning' in DLL 'StringUtilities.dll'.
    //       at Example.GoodMorning(String& name)
    //       at Example.Main()
    
    Module Example
       Declare Unicode Function GoodMorning Lib "StringUtilities.dll" (
          ByVal name As String) As String  
    
       Public Sub Main()
          Console.WriteLine(SayGoodMorning("Dakota"))
       End Sub
    End Module
    ' The example displays the following output:
    '    Unhandled Exception: System.EntryPointNotFoundException: Unable to find an entry point 
    '    named 'GoodMorning' in DLL 'StringUtilities.dll'.
    '       at Example.GoodMorning(String& name)
    '       at Example.Main()
    

    To eliminate the exception, add a reference to the managed assembly and access the StringUtilities.SayGoodMorning method just as you would access any other method in managed code, as the following example does.

    using System;
    
    public class Example
    {
       public static void Main()
       {
           Console.WriteLine(StringUtilities.SayGoodMorning("Dakota"));
       }
    }
    // The example displays the following output:
    //        A top of the morning to you, Dakota!
    
    Module Example
       Public Sub Main()
          Console.WriteLine(StringUtilities.SayGoodMorning("Dakota"))
       End Sub
    End Module
    ' The example displays the following output:
    '       A top of the morning to you, Dakota!
    
  • You are trying to call a method in a COM DLL as if it were a Windows DLL. To access a COM DLL, select the Add Reference option in Visual Studio to add a reference to the project, and then select the type library from the COM tab.

For a list of initial property values for an instance of EntryPointNotFoundException, see the EntryPointNotFoundException constructors.

Constructors

EntryPointNotFoundException() EntryPointNotFoundException() EntryPointNotFoundException() EntryPointNotFoundException()

Initializes a new instance of the EntryPointNotFoundException class.

EntryPointNotFoundException(SerializationInfo, StreamingContext) EntryPointNotFoundException(SerializationInfo, StreamingContext) EntryPointNotFoundException(SerializationInfo, StreamingContext) EntryPointNotFoundException(SerializationInfo, StreamingContext)

Initializes a new instance of the EntryPointNotFoundException class with serialized data.

EntryPointNotFoundException(String) EntryPointNotFoundException(String) EntryPointNotFoundException(String) EntryPointNotFoundException(String)

Initializes a new instance of the EntryPointNotFoundException class with a specified error message.

EntryPointNotFoundException(String, Exception) EntryPointNotFoundException(String, Exception) EntryPointNotFoundException(String, Exception) EntryPointNotFoundException(String, Exception)

Initializes a new instance of the EntryPointNotFoundException class with a specified error message and a reference to the inner exception that is the cause of this exception.

Properties

Data Data Data Data

Gets a collection of key/value pairs that provide additional user-defined information about the exception.

(Inherited from Exception)
HelpLink HelpLink HelpLink HelpLink

Gets or sets a link to the help file associated with this exception.

(Inherited from Exception)
HResult HResult HResult HResult

Gets or sets HRESULT, a coded numerical value that is assigned to a specific exception.

(Inherited from Exception)
InnerException InnerException InnerException InnerException

Gets the Exception instance that caused the current exception.

(Inherited from Exception)
Message Message Message Message

Gets the error message for this exception.

(Inherited from TypeLoadException)
Source Source Source Source

Gets or sets the name of the application or the object that causes the error.

(Inherited from Exception)
StackTrace StackTrace StackTrace StackTrace

Gets a string representation of the immediate frames on the call stack.

(Inherited from Exception)
TargetSite TargetSite TargetSite TargetSite

Gets the method that throws the current exception.

(Inherited from Exception)
TypeName TypeName TypeName TypeName

Gets the fully qualified name of the type that causes the exception.

(Inherited from TypeLoadException)

Methods

Equals(Object) Equals(Object) Equals(Object) Equals(Object)

Determines whether the specified object is equal to the current object.

(Inherited from Object)
GetBaseException() GetBaseException() GetBaseException() GetBaseException()

When overridden in a derived class, returns the Exception that is the root cause of one or more subsequent exceptions.

(Inherited from Exception)
GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Serves as the default hash function.

(Inherited from Object)
GetObjectData(SerializationInfo, StreamingContext) GetObjectData(SerializationInfo, StreamingContext) GetObjectData(SerializationInfo, StreamingContext) GetObjectData(SerializationInfo, StreamingContext)

Sets the SerializationInfo object with the class name, method name, resource ID, and additional exception information.

(Inherited from TypeLoadException)
GetType() GetType() GetType() GetType()

Gets the runtime type of the current instance.

(Inherited from Exception)
MemberwiseClone() MemberwiseClone() MemberwiseClone() MemberwiseClone()

Creates a shallow copy of the current Object.

(Inherited from Object)
ToString() ToString() ToString() ToString()

Creates and returns a string representation of the current exception.

(Inherited from Exception)

Events

SerializeObjectState SerializeObjectState SerializeObjectState SerializeObjectState

Occurs when an exception is serialized to create an exception state object that contains serialized data about the exception.

(Inherited from Exception)

Applies to

See Also