View return value?

Question

Say I have the following

int num = 40 + str2Int("30");

Is there anyway with visual studio 2008 to tell what Str2Int is returning without stepping into the function and going to the return?

Answer 1

In the "auto" variable windows it will display the result of any operations you just stepped over.

Edit: Removed uncertainty over the location of this (thanks goes to Michael Burr)

Answer 2

Since the return value is generally in the EAX register, you put the $eax 'variable' in the watch window. When you step over the function call, what's in EAX is what that function returned.

And if you also provide the hr format symbol the debugger will show you the HRESULT or Win32 error message (like "S_OK" or "Access is denied") instead of just the raw number. It can be handy to have each ($eax and $eax,hr) in separate watch entries.

Another useful entry is $err which shows whatever GetLastError() would return (and the hr format symbol can be applied to it - or anything - as well):

$eax
$eax,hr
$err
$err,hr

Note that older versions of the VS debugger might want you to use a @ instead of a $ to start these variables, but a member of the debugger team has stated that $ is preferred to keep things in line with the "Debugging Tools for Windows" toolset (I think that support for @ is deprecated and might be removed at some point).