ILGenerator.ThrowException(Type) Method
Definition
Important
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Emits an instruction to throw an exception.
public:
virtual void ThrowException(Type ^ excType);public virtual void ThrowException (Type excType);abstract member ThrowException : Type -> unit
override this.ThrowException : Type -> unitPublic Overridable Sub ThrowException (excType As Type)Parameters
- excType
- Type
The class of the type of exception to throw.
Exceptions
excType is not the Exception class or a derived class of Exception.
-or-
The type does not have a parameterless constructor.
excType is null.
Examples
The following code sample demonstrates the contextual usage of ThrowException to throw an exception inside the MSIL of a dynamic method.
using namespace System;
using namespace System::Threading;
using namespace System::Reflection;
using namespace System::Reflection::Emit;
int main()
{
AppDomain^ myDomain = Thread::GetDomain();
AssemblyName^ myAsmName = gcnew AssemblyName;
myAsmName->Name = "AdderExceptionAsm";
AssemblyBuilder^ myAsmBldr = myDomain->DefineDynamicAssembly( myAsmName,
AssemblyBuilderAccess::RunAndSave );
ModuleBuilder^ myModBldr = myAsmBldr->DefineDynamicModule( myAsmName->Name,
myAsmName->Name + ".dll" );
TypeBuilder^ myTypeBldr = myModBldr->DefineType( "Adder" );
array<Type^>^adderParams = {int::typeid,int::typeid};
// This method will add two numbers which are 100 or less. If either of the
// passed integer vales are greater than 100, it will throw an exception.
MethodBuilder^ adderBldr = myTypeBldr->DefineMethod( "DoAdd",
static_cast<MethodAttributes>(MethodAttributes::Public | MethodAttributes::Static),
int::typeid, adderParams );
ILGenerator^ adderIL = adderBldr->GetILGenerator();
// Types and methods used in the code to throw, catch, and
// display OverflowException. Note that if the catch block were
// for a more general type, such as Exception, we would need
// a MethodInfo for that type's ToString method.
//
Type^ overflow = OverflowException::typeid;
ConstructorInfo^ exCtorInfo = overflow->GetConstructor(
gcnew array<Type^> { String::typeid });
MethodInfo^ exToStrMI = overflow->GetMethod( "ToString" );
MethodInfo^ writeLineMI = Console::typeid->GetMethod( "WriteLine",
gcnew array<Type^> { String::typeid, Object::typeid } );
LocalBuilder^ tmp1 = adderIL->DeclareLocal( int::typeid );
LocalBuilder^ tmp2 = adderIL->DeclareLocal( overflow );
// In order to successfully branch, we need to create labels
// representing the offset IL instruction block to branch to.
// These labels, when the MarkLabel(Label) method is invoked,
// will specify the IL instruction to branch to.
//
Label failed = adderIL->DefineLabel();
Label endOfMthd = adderIL->DefineLabel();
// Begin the try block.
Label exBlock = adderIL->BeginExceptionBlock();
// First, load argument 0 and the integer value of S"100" onto the
// stack. If arg0 > 100, branch to the label S"failed", which is marked
// as the address of the block that throws an exception.
adderIL->Emit( OpCodes::Ldarg_0 );
adderIL->Emit( OpCodes::Ldc_I4_S, 100 );
adderIL->Emit( OpCodes::Bgt_S, failed );
// Now, check to see if argument 1 was greater than 100. If it was,
// branch to S"failed." Otherwise, fall through and perform the addition,
// branching unconditionally to the instruction at the label S"endOfMthd".
adderIL->Emit( OpCodes::Ldarg_1 );
adderIL->Emit( OpCodes::Ldc_I4_S, 100 );
adderIL->Emit( OpCodes::Bgt_S, failed );
adderIL->Emit( OpCodes::Ldarg_0 );
adderIL->Emit( OpCodes::Ldarg_1 );
adderIL->Emit( OpCodes::Add_Ovf_Un );
// Store the result of the addition.
adderIL->Emit( OpCodes::Stloc_S, tmp1 );
adderIL->Emit( OpCodes::Br_S, endOfMthd );
// If one of the arguments was greater than 100, we need to throw an
// exception. We'll use "OverflowException" with a customized message.
// First, we load our message onto the stack, and then create a new
// exception Object using the constructor overload that accepts a
// String* message.
adderIL->MarkLabel( failed );
adderIL->Emit( OpCodes::Ldstr, "Cannot accept values over 100 for add." );
adderIL->Emit( OpCodes::Newobj, exCtorInfo );
// We're going to need to refer to that exception Object later, so let's
// store it in a temporary variable. Since the store function pops the
// the value/reference off the stack, and we'll need it to throw the
// exception, we will subsequently load it back onto the stack as well.
adderIL->Emit( OpCodes::Stloc_S, tmp2 );
adderIL->Emit( OpCodes::Ldloc_S, tmp2 );
// Throw the exception now on the stack.
adderIL->ThrowException( overflow );
// Start the catch block for OverflowException.
//
adderIL->BeginCatchBlock( overflow );
// When we enter the catch block, the thrown exception
// is on the stack. Store it, then load the format string
// for WriteLine.
//
adderIL->Emit(OpCodes::Stloc_S, tmp2);
adderIL->Emit(OpCodes::Ldstr, "Caught {0}");
// Push the thrown exception back on the stack, then
// call its ToString() method. Note that if this catch block
// were for a more general exception type, like Exception,
// it would be necessary to use the ToString for that type.
//
adderIL->Emit(OpCodes::Ldloc_S, tmp2);
adderIL->EmitCall(OpCodes::Callvirt, exToStrMI, nullptr);
// The format string and the return value from ToString() are
// now on the stack. Call WriteLine(string, object).
//
adderIL->EmitCall( OpCodes::Call, writeLineMI, nullptr );
// Since our function has to return an integer value, we'll load -1 onto
// the stack to indicate an error, and store it in local variable tmp1.
adderIL->Emit( OpCodes::Ldc_I4_M1 );
adderIL->Emit( OpCodes::Stloc_S, tmp1 );
// End the exception handling block.
adderIL->EndExceptionBlock();
// The end of the method. If no exception was thrown, the correct value
// will be saved in tmp1. If an exception was thrown, tmp1 will be equal
// to -1. Either way, we'll load the value of tmp1 onto the stack and return.
adderIL->MarkLabel( endOfMthd );
adderIL->Emit( OpCodes::Ldloc_S, tmp1 );
adderIL->Emit( OpCodes::Ret );
Type^ adderType = myTypeBldr->CreateType();
Object^ addIns = Activator::CreateInstance( adderType );
array<Object^>^addParams = gcnew array<Object^>(2);
Console::Write( "Enter an integer value: " );
addParams[ 0 ] = Convert::ToInt32( Console::ReadLine() );
Console::Write( "Enter another integer value: " );
addParams[ 1 ] = Convert::ToInt32( Console::ReadLine() );
Console::WriteLine( "If either integer was > 100, an exception will be thrown." );
Console::WriteLine( "---" );
Console::WriteLine( " {0} + {1} = {2}", addParams[ 0 ], addParams[ 1 ], adderType->InvokeMember( "DoAdd", BindingFlags::InvokeMethod, nullptr, addIns, addParams ) );
}
/* This code produces output similar to the following:
Enter an integer value: 24
Enter another integer value: 101
If either integer was > 100, an exception will be thrown.
---
Caught System.OverflowException: Arithmetic operation resulted in an overflow.
at Adder.DoAdd(Int32 , Int32 )
24 + 101 = -1
*/
using System;
using System.Reflection;
using System.Reflection.Emit;
class ILThrowExceptionDemo
{
public static void Main()
{
AppDomain current = AppDomain.CurrentDomain;
AssemblyName myAsmName = new AssemblyName();
myAsmName.Name = "AdderExceptionAsm";
AssemblyBuilder myAsmBldr = current.DefineDynamicAssembly(myAsmName,
AssemblyBuilderAccess.RunAndSave);
ModuleBuilder myModBldr = myAsmBldr.DefineDynamicModule(myAsmName.Name,
myAsmName.Name + ".dll");
TypeBuilder myTypeBldr = myModBldr.DefineType("Adder");
Type[] adderParams = new Type[] {typeof(int), typeof(int)};
// This method will add two numbers which are 100 or less. If either of the
// passed integer vales are greater than 100, it will throw an exception.
MethodBuilder adderBldr = myTypeBldr.DefineMethod("DoAdd",
MethodAttributes.Public |
MethodAttributes.Static,
typeof(int),
adderParams);
ILGenerator adderIL = adderBldr.GetILGenerator();
// Types and methods used in the code to throw, catch, and
// display OverflowException. Note that if the catch block were
// for a more general type, such as Exception, we would need
// a MethodInfo for that type's ToString method.
//
Type overflow = typeof(OverflowException);
ConstructorInfo exCtorInfo = overflow.GetConstructor(
new Type[]
{typeof(string)});
MethodInfo exToStrMI = overflow.GetMethod("ToString");
MethodInfo writeLineMI = typeof(Console).GetMethod("WriteLine",
new Type[]
{typeof(string),
typeof(object)});
LocalBuilder tmp1 = adderIL.DeclareLocal(typeof(int));
LocalBuilder tmp2 = adderIL.DeclareLocal(overflow);
// In order to successfully branch, we need to create labels
// representing the offset IL instruction block to branch to.
// These labels, when the MarkLabel(Label) method is invoked,
// will specify the IL instruction to branch to.
//
Label failed = adderIL.DefineLabel();
Label endOfMthd = adderIL.DefineLabel();
// Begin the try block.
Label exBlock = adderIL.BeginExceptionBlock();
// First, load argument 0 and the integer value of "100" onto the
// stack. If arg0 > 100, branch to the label "failed", which is marked
// as the address of the block that throws an exception.
//
adderIL.Emit(OpCodes.Ldarg_0);
adderIL.Emit(OpCodes.Ldc_I4_S, 100);
adderIL.Emit(OpCodes.Bgt_S, failed);
// Now, check to see if argument 1 was greater than 100. If it was,
// branch to "failed." Otherwise, fall through and perform the addition,
// branching unconditionally to the instruction at the label "endOfMthd".
//
adderIL.Emit(OpCodes.Ldarg_1);
adderIL.Emit(OpCodes.Ldc_I4_S, 100);
adderIL.Emit(OpCodes.Bgt_S, failed);
adderIL.Emit(OpCodes.Ldarg_0);
adderIL.Emit(OpCodes.Ldarg_1);
adderIL.Emit(OpCodes.Add_Ovf_Un);
// Store the result of the addition.
adderIL.Emit(OpCodes.Stloc_S, tmp1);
adderIL.Emit(OpCodes.Br_S, endOfMthd);
// If one of the arguments was greater than 100, we need to throw an
// exception. We'll use "OverflowException" with a customized message.
// First, we load our message onto the stack, and then create a new
// exception object using the constructor overload that accepts a
// string message.
//
adderIL.MarkLabel(failed);
adderIL.Emit(OpCodes.Ldstr, "Cannot accept values over 100 for add.");
adderIL.Emit(OpCodes.Newobj, exCtorInfo);
// We're going to need to refer to that exception object later, so let's
// store it in a temporary variable. Since the store function pops the
// the value/reference off the stack, and we'll need it to throw the
// exception, we will subsequently load it back onto the stack as well.
adderIL.Emit(OpCodes.Stloc_S, tmp2);
adderIL.Emit(OpCodes.Ldloc_S, tmp2);
// Throw the exception now on the stack.
adderIL.ThrowException(overflow);
// Start the catch block for OverflowException.
//
adderIL.BeginCatchBlock(overflow);
// When we enter the catch block, the thrown exception
// is on the stack. Store it, then load the format string
// for WriteLine.
//
adderIL.Emit(OpCodes.Stloc_S, tmp2);
adderIL.Emit(OpCodes.Ldstr, "Caught {0}");
// Push the thrown exception back on the stack, then
// call its ToString() method. Note that if this catch block
// were for a more general exception type, like Exception,
// it would be necessary to use the ToString for that type.
//
adderIL.Emit(OpCodes.Ldloc_S, tmp2);
adderIL.EmitCall(OpCodes.Callvirt, exToStrMI, null);
// The format string and the return value from ToString() are
// now on the stack. Call WriteLine(string, object).
//
adderIL.EmitCall(OpCodes.Call, writeLineMI, null);
// Since our function has to return an integer value, we'll load -1 onto
// the stack to indicate an error, and store it in local variable tmp1.
//
adderIL.Emit(OpCodes.Ldc_I4_M1);
adderIL.Emit(OpCodes.Stloc_S, tmp1);
// End the exception handling block.
adderIL.EndExceptionBlock();
// The end of the method. If no exception was thrown, the correct value
// will be saved in tmp1. If an exception was thrown, tmp1 will be equal
// to -1. Either way, we'll load the value of tmp1 onto the stack and return.
//
adderIL.MarkLabel(endOfMthd);
adderIL.Emit(OpCodes.Ldloc_S, tmp1);
adderIL.Emit(OpCodes.Ret);
Type adderType = myTypeBldr.CreateType();
object addIns = Activator.CreateInstance(adderType);
object[] addParams = new object[2];
Console.Write("Enter an integer value: ");
addParams[0] = (object)Convert.ToInt32(Console.ReadLine());
Console.Write("Enter another integer value: ");
addParams[1] = (object)Convert.ToInt32(Console.ReadLine());
Console.WriteLine("If either integer was > 100, an exception will be thrown.");
Console.WriteLine("---");
Console.WriteLine("{0} + {1} = {2}",
addParams[0], addParams[1],
adderType.InvokeMember("DoAdd",
BindingFlags.InvokeMethod,
null,
addIns,
addParams));
}
}
/* This code produces output similar to the following:
Enter an integer value: 24
Enter another integer value: 101
If either integer was > 100, an exception will be thrown.
---
Caught System.OverflowException: Arithmetic operation resulted in an overflow.
at Adder.DoAdd(Int32 , Int32 )
24 + 101 = -1
*/
Imports System.Reflection
Imports System.Reflection.Emit
Class ILThrowExceptionDemo
Public Shared Sub Main()
Dim current As AppDomain = AppDomain.CurrentDomain
Dim myAsmName As New AssemblyName()
myAsmName.Name = "AdderExceptionAsm"
Dim myAsmBldr As AssemblyBuilder = _
current.DefineDynamicAssembly(myAsmName, _
AssemblyBuilderAccess.RunAndSave)
Dim myModBldr As ModuleBuilder = _
myAsmBldr.DefineDynamicModule(myAsmName.Name, _
myAsmName.Name & ".dll")
Dim myTypeBldr As TypeBuilder = myModBldr.DefineType("Adder")
Dim adderParams() As Type = {GetType(Integer), GetType(Integer)}
' This method will add two numbers which are 100 or less. If either of the
' passed integer vales are greater than 100, it will throw an exception.
Dim adderBldr As MethodBuilder = myTypeBldr.DefineMethod("DoAdd", _
MethodAttributes.Public Or MethodAttributes.Static, _
GetType(Integer), adderParams)
Dim adderIL As ILGenerator = adderBldr.GetILGenerator()
' Types and methods used in the code to throw, catch, and
' display OverflowException. Note that if the catch block were
' for a more general type, such as Exception, we would need
' a MethodInfo for that type's ToString method.
'
Dim overflow As Type = GetType(OverflowException)
Dim exCtorInfo As ConstructorInfo = overflow.GetConstructor( _
New Type() {GetType(String)})
Dim exToStrMI As MethodInfo = overflow.GetMethod("ToString")
Dim writeLineMI As MethodInfo = GetType(Console).GetMethod("WriteLine", _
New Type() {GetType(String), _
GetType(Object)})
Dim tmp1 As LocalBuilder = adderIL.DeclareLocal(GetType(Integer))
Dim tmp2 As LocalBuilder = adderIL.DeclareLocal(overflow)
' In order to successfully branch, we need to create labels
' representing the offset IL instruction block to branch to.
' These labels, when the MarkLabel(Label) method is invoked,
' will specify the IL instruction to branch to.
'
Dim failed As Label = adderIL.DefineLabel()
Dim endOfMthd As Label = adderIL.DefineLabel()
' Begin the try block.
Dim exBlock As Label = adderIL.BeginExceptionBlock()
' First, load argument 0 and the integer value of "100" onto the
' stack. If arg0 > 100, branch to the label "failed", which is marked
' as the address of the block that throws an exception.
'
adderIL.Emit(OpCodes.Ldarg_0)
adderIL.Emit(OpCodes.Ldc_I4_S, 100)
adderIL.Emit(OpCodes.Bgt_S, failed)
' Now, check to see if argument 1 was greater than 100. If it was,
' branch to "failed." Otherwise, fall through and perform the addition,
' branching unconditionally to the instruction at the label "endOfMthd".
'
adderIL.Emit(OpCodes.Ldarg_1)
adderIL.Emit(OpCodes.Ldc_I4_S, 100)
adderIL.Emit(OpCodes.Bgt_S, failed)
adderIL.Emit(OpCodes.Ldarg_0)
adderIL.Emit(OpCodes.Ldarg_1)
adderIL.Emit(OpCodes.Add_Ovf_Un)
' Store the result of the addition.
adderIL.Emit(OpCodes.Stloc_S, tmp1)
adderIL.Emit(OpCodes.Br_S, endOfMthd)
' If one of the arguments was greater than 100, we need to throw an
' exception. We'll use "OverflowException" with a customized message.
' First, we load our message onto the stack, and then create a new
' exception object using the constructor overload that accepts a
' string message.
adderIL.MarkLabel(failed)
adderIL.Emit(OpCodes.Ldstr, "Cannot accept values over 100 for add.")
adderIL.Emit(OpCodes.Newobj, exCtorInfo)
' Throw the exception now on the stack.
adderIL.ThrowException(overflow)
' Start the catch block for OverflowException.
'
adderIL.BeginCatchBlock(overflow)
' When we enter the catch block, the thrown exception
' is on the stack. Store it, then load the format string
' for WriteLine.
'
adderIL.Emit(OpCodes.Stloc_S, tmp2)
adderIL.Emit(OpCodes.Ldstr, "Caught {0}")
' Push the thrown exception back on the stack, then
' call its ToString() method. Note that if this catch block
' were for a more general exception type, like Exception,
' it would be necessary to use the ToString for that type.
'
adderIL.Emit(OpCodes.Ldloc_S, tmp2)
adderIL.EmitCall(OpCodes.Callvirt, exToStrMI, Nothing)
' The format string and the return value from ToString() are
' now on the stack. Call WriteLine(string, object).
'
adderIL.EmitCall(OpCodes.Call, writeLineMI, Nothing)
' Since our function has to return an integer value, load -1 onto
' the stack to indicate an error, and store it in local variable
' tmp1.
adderIL.Emit(OpCodes.Ldc_I4_M1)
adderIL.Emit(OpCodes.Stloc_S, tmp1)
' End the exception handling block.
adderIL.EndExceptionBlock()
' The end of the method. If no exception was thrown, the correct value
' will be saved in tmp1. If an exception was thrown, tmp1 will be equal
' to -1. Either way, we'll load the value of tmp1 onto the stack and return.
'
adderIL.MarkLabel(endOfMthd)
adderIL.Emit(OpCodes.Ldloc_S, tmp1)
adderIL.Emit(OpCodes.Ret)
Dim adderType As Type = myTypeBldr.CreateType()
Dim addIns As Object = Activator.CreateInstance(adderType)
Dim addParams(1) As Object
Console.Write("Enter an integer value: ")
addParams(0) = CType(Convert.ToInt32(Console.ReadLine()), Object)
Console.Write("Enter another integer value: ")
addParams(1) = CType(Convert.ToInt32(Console.ReadLine()), Object)
Console.WriteLine("If either integer was > 100, an exception will be thrown.")
Console.WriteLine("---")
Console.WriteLine("{0} + {1} = {2}", addParams(0), addParams(1), _
adderType.InvokeMember("DoAdd", BindingFlags.InvokeMethod, _
Nothing, addIns, addParams))
End Sub
End Class
' This code example produces output similar to the following:
'
'Enter an integer value: 24
'Enter another integer value: 101
'If either integer was > 100, an exception will be thrown.
'---
'Caught System.OverflowException: Arithmetic operation resulted in an overflow.
' at Adder.DoAdd(Int32 , Int32 )
'24 + 101 = -1
Applies to
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