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Enhanced Debugging Info For VS6/7
Submitted by |
Hello all,
My buddy and I found this tip while messing with Visual Studio's
autoexp.dat file and we thought we'd share it with our fellow
flipcoders. For those who don't know it, autoexp.dat (in the
Common7\Packages\Debugger directory for VC7 or Common\MSDev98\Bin for
VC6) is a text file used by the debugger to figure out what information
to display in the 'Value' field of the debug windows (this, locals,
watch1, etc...).
Normally, the debugger writes '{...}' as the value of an object, but
with autoexp.dat, it will instead write specific information: For
instance, in the case of a CPoint object where x=5 and y=-2, it will
write '{x=5 y=-2}' in that field, in place of '{...}'.
The advantage is obvious: you don't have to hit the + sign and look at
the values of the member variables x and y yourself. It saves clicks and
space.
Here is what the entry looks like for a CPoint object in autoexp.dat:
[...]
CPoint =x= y= ; <-- will display: {x=5 y=-2}
[...]
And so autoexp.dat defines what information the debugger should display
for many types, among which is std::basic_string<...>. In that
particular case, it displays the value of the _Bx._Buf member variable.
Here is the entry for strings (in VC7):
[...]
std::basic_string,std::allocator
>=<_Bx._Buf> ; <-- will display: '{"Hello World"}'
[...]
And that's already wonderful, but as probably a lot of you have noticed,
VC7 doesn't do really well with strings, sometimes it displays the right
info, sometimes it doesn't.
The reason is that (in VC7) strings have two ways of storing the string
data: locally, in a 16-byte buffer (_Bx._Buf) or dynamically through a
pointer (_Bx._Ptr). That way, if your string is short enough (less than
15 characters), the string object will not need to allocate memory on
the heap and you can take full advantage of inline constructor (in
general).
Unfortunately, the debugger doesn't know how which one of _Buf or _Ptr
it should display in the 'Value' field of the watch window, and the
simple syntax of Autoexp.dat does not support conditional expressions.
Fortunately, and that is what we would like to share with the community,
Microsoft implemented an Addin library support for the debugger, and in
our case for the 'evaluation' of objects and variables.
Indeed, it is possible to tell the debugger to use an external library
to figure out the information to display. The following entry, in
autoexp.dat
[...]
_SYSTEMTIME=$ADDIN(EEAddIn.dll,AddIn_SystemTime)
[...]
tells the debugger that in the case of a _SYSTEMTIME variable, it should
call the 'AddIn_SystemTime' function of the 'EEAddIn.dll' library
(located in the Common7\IDE folder for VC7 or Common\IDE\IDE98 for VC6).
The library then takes care of converting the data into a string of
characters that the debugger will display in the 'Value' field of the
watch window.
There actually is an help page (and a sample project) on how to build
such a dll in the VC7 help (search for "EEAddIn"), but we thought we'd
share our attempt at making one for strings (to cope with the problem of
_Buf and _Ptr under VC7).
To use our dll file:
In autoexp.dat ("C:\Program Files\Microsoft Visual Studio .NET\
Common7\Packages\Debugger\autoexp.dat"), find the following entry:
std::basic_string,std::allocator
>=<_Bx._Buf>
and replace it by:
; comment the old version
; std::basic_string,std::allocator
>=<_Bx._Buf>
std::basic_string,std::allocator
>=$ADDIN(VSPCoreAddin.dll, AddIn_String)
Then copy the VSPCoreAddin.dll file to the "C:\Program Files\Microsoft
Visual Studio .NET\Common7\IDE" directory. That's it.
You can also have a look at our source code and implement your own
complex data evaluation functions (for VC6 or VC7), just unzip the file
and open the project.
The project is available here: VSPCoreAddIn.zip (208k)
We hope this will be useful.
Jean Simonet
Olivier Basille
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The zip file viewer built into the Developer Toolbox made use
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