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ICorDebugILFrame3::GetReturnValueForILOffset Method

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Gets an "ICorDebugValue" object that encapsulates the return value of a function.

Syntax

HRESULT GetReturnValueForILOffset(  
    ULONG32 ILoffset,
    [out] ICorDebugValue **ppReturnValue  
);

Parameters

ILOffset
The IL offset. See the Remarks section.

ppReturnValue
A pointer to the address of an "ICorDebugValue" interface object that provides information about the return value of a function call.

Remarks

This method is used along with the ICorDebugCode3::GetReturnValueLiveOffset method to get the return value of a method. It is particularly useful in the case of methods whose return values are ignored, as in the following two code examples. The first example calls the Int32.TryParse method, but ignores the method's return value.

private static int ConvertNumericString(string s)
{
   int number;
   if (s.Trim().Length == 8)
      Int32.TryParse(s, System.Globalization.NumberStyles.HexNumber,
                     null, out number);
   else
      Int32.TryParse(s, out number);

   return number;
}

Private Function ConvertNumericString(s As String) As Integer
    Dim number As Integer
    If s.Trim().Length = 8 Then
        Int32.TryParse(s, System.Globalization.NumberStyles.HexNumber,
                       Nothing, number)
    Else
        Int32.TryParse(s, number)
    End If
    Return number
End Function

The second example illustrates a much more common problem in debugging. Because a method is used as an argument in a method call, its return value is accessible only when the debugger steps through the called method. In many cases, particularly when the called method is defined in an external library, that is not possible.

using System;

public class Example
{
   private static Random rnd;

   public static void Main()
   {
      rnd = new Random();
      Example ex = new Example();
      double value = MathLib.GetComputedValue(ex.GetInt(), ex.GetDouble());
      Console.WriteLine(value);
   }

   private int GetInt()
   {
      return rnd.Next(11, 100);
   }

   private double GetDouble()
   {
      return rnd.NextDouble();
   }
}

Public Module Example
    Dim rnd As Random

    Public Sub Main()
        rnd = New Random()
        Dim value As Double = MathLib.GetComputedValue(GetInt(), GetDouble())
        Console.WriteLine(value)
    End Sub

    Private Function GetInt() As Integer
        Return rnd.Next(11, 100)
    End Function

    Private Function GetDouble() As Double
        Return rnd.NextDouble()
    End Function
End Module

If you pass the ICorDebugCode3::GetReturnValueLiveOffset method an IL offset to a function call site, it returns one or more native offsets. The debugger can then set breakpoints on these native offsets in the function. When the debugger hits one of the breakpoints, you can then pass the same IL offset that you passed to this method to get the return value. The debugger should then clear all the breakpoints that it set.

Warning

The ICorDebugCode3::GetReturnValueLiveOffset Method and ICorDebugILFrame3::GetReturnValueForILOffset methods allow you to get return value information for reference types only. Retrieving return value information from value types (that is, all types that derive from ValueType) is not supported.

The IL offset specified by the ILOffset parameter should be at a function call site, and the debuggee should be stopped at a breakpoint set at the native offset returned by the ICorDebugCode3::GetReturnValueLiveOffset method for the same IL offset. If the debuggee is not stopped at the correct location for the specified IL offset, the API will fail.

If the function call doesn't return a value, the API will fail.

The ICorDebugILFrame3::GetReturnValueForILOffset method is available only on x86-based and AMD64 systems.

Requirements

Platforms: See System Requirements.

Header: CorDebug.idl, CorDebug.h

Library: CorGuids.lib

.NET Framework Versions: Available since 4.5.1

See also