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I would like to inspect a method's return value without having to re-execute the method itself. I believe my only option is to use the disassembler. I came to this conclusion after reading the responses to Stackflow question Getting a Method's Return Value in the VS Debugger.

I think the value in register EAX is my return value. How do I inspect the object pointed to by EAX in the debugger? Here is my disassembled return statement.

   30:             return SomeString();
000001bb  mov         ecx,dword ptr [ebp-3Ch] 
000001be  call        FFF7A320 
000001c3  mov         dword ptr [ebp-78h],eax 
000001c6  mov         eax,dword ptr [ebp-78h] 
000001c9  mov         dword ptr [ebp-4Ch],eax 
000001cc  nop 
000001cd  jmp         000001D8 
000001cf  mov         dword ptr [ebp-1Ch],0 
000001d6  jmp         000001BA 
    31:         }
000001d8  mov         eax,dword ptr [ebp-4Ch] 
000001db  lea         esp,[ebp-0Ch] 
000001de  pop         ebx 
000001df  pop         esi 
000001e0  pop         edi 
000001e1  pop         ebp 
000001e2  ret
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Don
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2 Answers2

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From the Registers window, select the EAX register value and hit Ctrl+C. Debug + Windows + Memory + Memory 1. In the Address text box, type 0x, Ctrl+V, type +12. The +12 skips the System.Object header. You should have little trouble reading it on the right if it contains ASCII characters, ignore the nulls.

Hans Passant
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  • You can also right click the memory window and select the format of the data that is contained there, you can choose to see the memory dump as int8, int16, int32, int64 , ASCII, Unicode, etc – Carlos Muñoz Aug 03 '10 at 17:10
  • Yes that does work, but this is too low a level. What happens when I have a more complex object? Is there anyway to cast the value in EAX to the type defined in the signature of the method? In my current example the type would be string. – Don Aug 03 '10 at 17:11
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    The normal debug expression would look like `*(string*)0x017316F8`. This however doesn't work for managed object references. It's a bummer. Post feedback to connect.microsoft.com – Hans Passant Aug 03 '10 at 17:24
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ISTR [EAX] in the variable watch window displays the EAX register.

sbi
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  • I can see the value of the register, but what I want to see is the object the value is pointing to. In my case I know it's a C# string. – Don Aug 03 '10 at 15:56
  • @Martin: Just cast the address to the type you expect it to be . – sbi Aug 03 '10 at 15:58
  • I develop in C#, so using registers in the debugger is foreign to me. Could you give me an example? I have EAX = 023964F4, I believe that's my object reference. – Don Aug 03 '10 at 16:13
  • I can display memory to see the object as hex and ascii, but that's too low level. – Don Aug 03 '10 at 16:18
  • In the immediate window I execute "0x023964f4 as System.String" which gives me a conversion error: Cannot convert type 'int' to 'string' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion – Don Aug 03 '10 at 16:19
  • @Martin: What's with `(System.String)0x023964f4`? (Or even `(System.String)[EAX]`?) – sbi Aug 03 '10 at 16:31
  • (System.String)0x023964f4 return the same error message. And (System.String)[EAX] returns 'string' is a 'type', which is not valid in the given context. – Don Aug 03 '10 at 16:41
  • @Martin: Sorry, I'm mostly a C++ VS user and am way out of my depth in C# waters. – sbi Aug 03 '10 at 16:52