5 Advanced Debugger Usage With Visual Studio NET

5. Advanced Debugger Usage With Visual Studio. NET Book: Debugging Applications for Microsoft. NET and Microsoft Windows

Agenda • Breakpoints • Advanced Breakpoints – Breakpoint Tips – Quickly Breaking Any Function. – Location Breakpoint Modifiers. – Multiple Breakpoints on a Single Line

Agenda (cont’d) • The Watch Window – Calling methods in a watch window – The Set Next Statement Command • Summary

Introduction “The whole key to debugging effectively is to avoid the debugger as much as possible because that’s where you waste all your time. ” Says…. John Robbins

DEBUGGER • When to use it? – Never on self-code…. . • Code you write is undoubtedly PERFECT. – Always on co-worker’s code.

THE WINDOWS DEBUGGER • Finally ONE debugger that handles – SCRIPT – ASP, ASP. NET – XML Web Services – Native Code – SQL debugging.

BREAKPOINTS • First “F 9” … then “F 10” • Def : – The position in code where your debugger assumes CONTROL of the program. • Location Breakpoint – The type of the breakpoints that we use regularly. (go to the margin and press F 9)

BREAKPOINTS • What happens when we set a breakpoint? – When code for such a line executes, the debugger will stop at that location. – So……WHY NOT SET BREAKPOINTS RANDOMLY ? – Absolutely NO HARM…… – Also…. . NO BIG USE !!!

BREAKPOINTS • A simple, yet effective breakpoint is extremely powerful , and with just that it alone, 99. 46% of all bugs are solved.

Ok ! First Set a breakpoint…then what? ? ? • What does a breakpoint tell the programmer? – The line where the breakpoint is set ; ) – The values of all the relevant variables till that point of code.

Scenario ! • Consider this piece of code { • for(int i = 1; i < 10000 ; i++){ j = j * (i+j); } } • What if I encounter a bug in the 10, 000’th iteration?

2 SIMPLE OPTIONS • 1. Code extra to display the value of the variables for each iteration. • 2. Set up a location breakpoint and stop at it each time for all the 10000 iterations. • Consequences – A swollen finger (take your pick). – Hours of unproductive work.

WHAT IF? • What if there was some way to tell the debugger to execute the code 9999 times before stopping? • ENTER SMART BREAKPOINTS

BREAKPOINT WINDOW CODES

BREAKPOINT TIPS • Breakpoints in the call stack window. – Useful especially to get stopped on recursion or deeply nested stacks. – Works very similar to that of a location breakpoint…. just in a another window. • Run To Cursor (Ctrl+F 10) – Breakpoint without setting a breakpoint. – Runs the program till where your cursor is and stops there.

BREAKPOINTS • Multiple breakpoints – Windows debugger supports multiple breakpoints (3)… • Take your cursor there and press F 9. • Only one RED button appears on the margin. • How does one differentiate between all the breakpoints in the same line? – BREAKPOINTS WINDOW

Quickly Breaking on any Function • In a million line code, how much time does it take to find out where a function is defined and set a breakpoint there? • The longer the code, the tougher it is to find out where a function is defined (spare the use of Ctrl+F & right click on function usage).

• How harder does it get if you want to add this breakpoint while you are already stepping through the code? • What if I just knew the class name or just the method name or maybe both? • The breakpoint window provides amazing help in this process. • You can simply set a breakpoint if you just know any of the method details. (not supported in. C++ completely)

THE BREAKPOINT WINDOW

ADD FUNCTION BREAKPOINT

Microsoft ! WE HAVE A PROBLEM!! • In the breakpoint window, to set a breakpoint • Type “<classname>. ” • VS. NET 2003 CRASHES

Setting breakpoints in the FCL • What if we set a breakpoint in a FCL class method by typing in the method with the class name in the break point window? – The WINDBG shows all the overloads for that method and gives you the option of setting breakpoints on any of them. • Ain’t that COOOOOL • Example : Console. Write. Line has 19 overloads.

Adding breakpoints to the FCL

LOCATION BREAKPOINT MODIFIERS, . ie. , SMART BREAKPOINTS • HIT COUNTS • CONDITIONAL EXPRESSIONS

HIT COUNTS • Consider this piece of code { for(int i = 1; i < 10000 ; i++){ j = j * (i+j); } } • What if I encounter a bug in the 10, 000’th iteration?

Adding SMARTS to BREAKPOINTS • Hit Count / Skip Count • This tells the debugger to stop at this breakpoint only after this line of code has executed the specified number of times.

HIT COUNT EVALUATION • Break always • Break when hit count is equal to. • Break when the hit count is equal to a multiple of. • Break when hit count is greater than or equal to.

CONDITIONAL EXPRESSIONS • • Another SMART to breakpoints. An alternative to writing extra code. Set a conditional expression. Make the breakpoint to occur only when the conditional expression – Makes a switch. – Condition evaluates to TRUE/FALSE

MULTIPLE BREAKPOINTS ON A SINGLE LINE For( I=0, m=0; I<10; I++, m--){ Console. Writeline(“I= {0} m = {1}”, I, m); } • Combining multiple breakpoints with conditional expressions.

WATCH WINDOW • A WATCH WINDOW IS NOT JUST A “WATCH WINDOW” • A watch window is not just for reading/ displaying the variable’s content. • The contents of the variable can be changed/cast into appropriate types at any point in a watch window.

WATCH WINDOW • Complete Expression Evaluator…. . BUILT IN !!! • Ability to replace looooooong expressions by sample simple relevant values.

CODE COVERAGE • A goal to strive while UNIT TESTING !! • Consider if ((e. Running == m_e. State)|| (e. Exception == m_e. State) && (TRUE == m_b. Seen. Loader))

• The watch window interprets this single IF condition as 3 separate lines of code. • The COOL part : – Change values of individual variables • The value of whole expression changes accordingly. – Different values that you want to test for gives you adequate code coverage.

Calling functions from WATCH WINDOW • WHY would I want to do that? ? • What if you want to simply check if an element’s value is valid or not? – Option 1 : write a function that checks for that and call it every time when that element is created/used. – Option 2: write the function…and use it only in the watch window (pre-release).

SO ! Where is the catch? • 20 SECONDS – Evaluation timed out! Errors • Killing threads. – Previous versions killed all related threads. • READ MEMORY ONLY FOR DATA VALIDATIONS.

SET NEXT • Available only when debugging. • Allows you to change the instruction pointer to a different place in the program. • Often called when you want to change an input parameter value to a data-structure. • HANDY TOOL during UNIT TESTING.

SET NEXT…. BUT BEWARE • Changing the state of the instruction pointer can easily send the program to CRASH.

SUMMARY • VS. NET debugging the state-of-the-art debugger in the market today. • Finally…. someone listened to their developers while developing software for them. • Common debugging styles to native code and managed code.

MORAL OF THE STORY USE THE. NET DEBUGGER MOST EFFECTIVELY TO USE IT THE LEAST NUMBER OF TIMES.

End of Presentation