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Posted 3 Apr 2012

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10+ Powerful Debugging Tricks with Visual Studio

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4.79/5 (163 votes)
18 Apr 2012CPOL5 min read
The article describes 10 time-saving debugging techniques available in Visual Studio.

Introduction

Debugging is a major part of the development lifecycle. Sometimes challenging, sometimes puzzling, sometimes annoying, one for sure - it is unavoidable for any not-so-trivial program. The progress of debugging tools over the last years has made many debugging tasks much easier and less time-consuming.

This article summarizes ten debugging tricks and techniques that can save you a lot of time when using Visual Studio.

1. Hover Mouse to Evaluate Expression

Image 1

Debugging can be challenging. Stepping through a function to understand what went wrong, looking through the call stack to see where did that value come from... In either case, adding watch expressions or looking through a list of locals can take quite a time. However, things get easier if you just point your mouse at a variable of interest. Moreover, classes and structures will be expanded with one click, allowing to find the field you need quickly and conveniently.

2. Change Values on-the-fly

Image 2

Debugger is much more than a tool for analyzing crashes and weird behavior. Many bugs can be prevented by stepping through a freshly written function and checking that it behaves as expected. Sometimes, you are curious "would the function behave correctly if this condition was true?". And in most cases, it does not mean changing the code and restarting. Just hover the mouse over a variable, double-click at the value and type in the new one!

3. Set Next Statement

Image 3

One typical debugging scenario is analyzing why a function calls fail by going through the function step-by-step. And what do you do when you've just discovered that a function called another function that returned an error? Restart debugging? There's a better idea: just drag the yellow statement marker to the line you want to be executed next, like the function that has just failed, and then simply step in. Simple, isn't it?

4. Edit and Continue

Image 4

Debugging a complex program, or a plugin? Found an error, but don't want to lose time stopping, rebuilding and restarting again and the function is called too often to use the previous trick each time? No problem, just fix the bug in-place and continue stepping. Visual Studio will modify your program and continue debugging with no need to restart.

Beware, though. Edit-and-continue has a bunch of known limitations. First, it won't work for 64-bit code. If it refuses to work for your C# app, go to project settings, Build page, then select "x86" as Platform Target. Don't worry, the Platform Target for the Release configuration is separate from the debug one and can still be "Any CPU".

Second, the edit-and-continue changes should be local, i.e., within one method. If you change the method signature, add new methods or classes, you'll have to restart the app, or undo the changes to continue. Changing methods containing lambda expressions implies modifying the auto-generated delegate classes and thus prevents continuing.

5. A Convenient Watch Window

Image 5

Probably, every modern debugger has a watch window. However, what's really cool about the Visual Studio one is how easily you can add and remove variables there. Just click at the empty line, type your expression and press Enter. Or simply press delete button to remove an expression that is no longer needed.

Moreover, the information you can get from the watch window is not limited to "normal" variables. You can enter $handles to track the amount of handles opened by your application (and find leaks easier), $err to see the error code of the last function (and then use Tools->Error Lookup to get a meaningful description), or @eax (@rax for 64-bit code) to see the register containing the return value of a function.

6. Annotated Disassembly

Image 6

Optimizing the performance of the critical parts of your program can be much easier using the interactive disassembly mode. Visual Studio shows you the instructions corresponding to every line of your code and allows running the code step-by-step, as well as setting breakpoints at arbitrary locations. And, of course, the expression evaluation and modification will work just like for the C++ code.

7. Threads Window with Stacks

Image 7

Debugging multi-threaded applications can be painful. Or it can be fun. Depends on your debugger. One really nice feature of Visual Studio 2010 is the stack view in the threads window. You can get a convenient overview of all your threads and navigate through their call stacks directly from the window.

8. Conditional Breakpoints

Image 8

If you're trying to reproduce a rare event and getting too many false positives with your breakpoints, you can easily make them conditional! Simply specify the condition for a breakpoint and Visual Studio will automatically ignore the breakpoint when the condition does not hold.

9. Memory Window

Image 9

Some bugs are caused by incorrect structure definitions, missing alignment attributes, etc. Seeing the raw memory contents simplifies locating and fixing those bugs. Visual Studio features a convenient memory window that can interpret the values as 8/16/32/64-bit numbers, as well as floating-point numbers and allows changing them on-the-fly by simply typing the new values over the old ones like in a text editor.

10. Go To Definition

Image 10

One last feature to mention is not directly related to debugging, rather to exploring big projects. If you are trying to find a bug in some code you have not written yourself, having a quick answer to "what is this type" or "what does this function do" can save you a lot of time. And Visual Studio does this with ease via the Go To Definition command.

11. Command Window

Image 11

This eleventh trick has been suggested by chaau and it can indeed save you a lot of time. Visual Studio supports a Command Window that can be activated through the View->Other Windows->Command Window menu. Once active, you can type various commands to automate the debugging. For example, you can easily evaluate an MFC COleDateTime variable by running a simple command:

? dt.Format("%Y-%m-%d %H:%M:%S")  

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Ivan Shcherbakov
Founder Sysprogs UG (haftungsbescrhänkt)
Germany Germany
Ivan Shcherbakov is a cofounder of the Sysprogs UG (haftungsbeschränkt), the company developing custom software, drivers and firmware and delivering VisualGDB - a Visual Studio plugin that allows using Visual Studio to build applications with GCC and debug them with GDB.

The main goal of VisualGDB is to combine the time-saving Visual Studio debugging experience with the wide application range of GDB, such as Linux applications and Embeddeed firmware.

A special Android Edition of VisualGDB allows building and debugging native Android code with Visual Studio easily and smoothly.

Comments and Discussions

 
GeneralRe: [My vote of 2] Blatant advertising of a commercial product (having free competition BTW.) Pin
Ivan Shcherbakov22-Dec-12 11:34
MemberIvan Shcherbakov22-Dec-12 11:34 
GeneralRe: [My vote of 2] Blatant advertising of a commercial product (having free competition BTW.) Pin
coder83422-Dec-12 13:08
Membercoder83422-Dec-12 13:08 
GeneralMy vote of 5 Pin
Purushotham Agaraharam19-Nov-12 18:30
MemberPurushotham Agaraharam19-Nov-12 18:30 
GeneralMy vote of 2 Pin
Lowell Walmsley30-Oct-12 5:41
MemberLowell Walmsley30-Oct-12 5:41 
GeneralThank you very much! Pin
Ross MacFarlane12-Oct-12 4:56
MemberRoss MacFarlane12-Oct-12 4:56 
GeneralSkilled worker already? Pin
iwbm3-Oct-12 6:21
Memberiwbm3-Oct-12 6:21 
GeneralNice, but almost nothing new Pin
xawari11-Jun-12 5:47
Memberxawari11-Jun-12 5:47 
QuestionMore tips Pin
Andrew Phillips6-Jun-12 15:26
MemberAndrew Phillips6-Jun-12 15:26 
Nice article, but it should be called "10 simple tips". I was expecting a few more powerful things (like something I didn't know). I will mention a few things though...

3. Set Next Statement

I am surprised at how many programmers do not know how to change the current instruction. This was always done using Ctrl+Shift-F10 in MS debugger. Even MS CodeView (MSDOS source level debugger) supported this. (Even before that you could just change the IP register.)

As the article states it is useful for going back and executing a function that you accidentally stepped over. But note that this may not work as expected if the function has side effects.

Also I find it especially useful for testing error-handling code where actually simulating the error is difficult. (Debuggers should not be used for debugging so much as verification - ie.stepping through the code to ensure it behaves as you expect.)

One thing to watch out for is not moving IP where the stack frame is in a different state (eg to very start or end of a function or into a different function). If you do this nasty things will happen when the function returns (if not before).

5 Watch window

Also, you can just select and drag a variable name or expression from the code into the watch window. This is even quicker than typing it in.

7. Call stacks in threads windows is a nice new feature of VS2010.

X. EAX register

One other trick I use is to show the registers window. If you have a breakpoint after a function call or you have stepped out of a function then the debugger will not show the return value of the function. However, the calling convention of C/C++ functions (most compilers) is to leave the return value in the EAX register.
Andrew Phillips
http://www.hexedit.com
andrew @ hexedit.com

QuestionGood work. Pin
neriacompany1-Jun-12 4:02
Memberneriacompany1-Jun-12 4:02 
GeneralMy Vote of 1 Pin
MacSpudster31-May-12 11:20
professionalMacSpudster31-May-12 11:20 
Question$err Pin
Joseph Mccornell29-May-12 1:03
MemberJoseph Mccornell29-May-12 1:03 
QuestionVery useful tips. Thanks Pin
dudoo28-May-12 14:12
Memberdudoo28-May-12 14:12 
GeneralMy vote of 5 Pin
Manoj Kumar Choubey17-May-12 22:51
professionalManoj Kumar Choubey17-May-12 22:51 
GeneralMy vote of 5 Pin
Ștefan-Mihai MOGA12-May-12 18:31
professionalȘtefan-Mihai MOGA12-May-12 18:31 
GeneralMy vote of 5 Pin
VMAtm11-May-12 21:38
MemberVMAtm11-May-12 21:38 
GeneralMy vote of 5 Pin
Monjurul Habib10-May-12 19:32
professionalMonjurul Habib10-May-12 19:32 
GeneralMy vote of 3 Pin
itaitai8-May-12 1:42
professionalitaitai8-May-12 1:42 
Questiontip Pin
Dave Kerr7-May-12 21:31
mentorDave Kerr7-May-12 21:31 
GeneralGreat tips Pin
BigDaveDev11-Apr-12 19:27
MemberBigDaveDev11-Apr-12 19:27 
QuestionEdit and Continue Pin
asit4u1111-Apr-12 3:01
Memberasit4u1111-Apr-12 3:01 
AnswerRe: Edit and Continue Pin
Ivan Shcherbakov18-Apr-12 21:09
MemberIvan Shcherbakov18-Apr-12 21:09 
QuestionAttaboy! Pin
David Crow10-Apr-12 5:39
MemberDavid Crow10-Apr-12 5:39 
QuestionFantastic! Pin
Member 42896139-Apr-12 23:29
MemberMember 42896139-Apr-12 23:29 
AnswerRe: Fantastic! Pin
Member 428961310-Apr-12 0:36
MemberMember 428961310-Apr-12 0:36 
AnswerRe: Fantastic! Pin
Ivan Shcherbakov18-Apr-12 21:10
MemberIvan Shcherbakov18-Apr-12 21:10 

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