BIM313 – Advanced Programming Techniques

Debugging

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Contents

• Debugging and Error Handling– Debugging feature in Visual Studio– try … catch … finally

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Debugging and Error Handling

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Error Types

• Syntax Errors– Forgetting semicolon, not closing parentheses or

curly braces, writing variable name incorrectly, etc.– Program is not compiled– Examine the compiler errors and correct the codes

• Logical Errors– Program is compiled– Program does not give the desired output– Debug your program!

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Debugging in Visual Studio

• Put breakpoints in your code– F9, click at the beginning of a line, Debug menu

• Start your program in Debug mode– F5 (not Ctrl-F5), Play arrow in toolbar, Debug

menu• Press F10 for single step• Press F11 to enter a function• End debugging with Shift-F5 or Stop in toolbar

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Monitoring Variable Content

• Move cursor an a variable while program is being debugged

• Follow the variables in the Locals and Autos windows

• Add variables into the Watch windows• Use the Immediate Window– Write the name of the variable and press Enter– You can call functions and expressions too

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Configurations

• Debug– Extra symbols are included in the executable file so

that it can be debugged– Runs slowly– Executable file size larger

• Release– Runs faster– Executable file size smaller– Use this configuration on the last build (before

distributing your program)7

Debugging Without a Debugger

• A debugger (e.g. Visual Studio) makes debugging easier

• If you don’t have an IDE, you can use Console.WriteLine() to debug your programs

• Just call Console.WriteLine() to print variables or some useful messages

• Don’t forget to remove those lines in the last build

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Debugging in Nonbreaking (Normal) Mode

Console.WriteLine("MyFunc() Function about to be called.");MyFunc("Do something.");Console.WriteLine("MyFunc() Function execution completed.");

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Some Advanced Topics

• Debug.WriteLine() / Trace.WriteLine()• Debug.WriteLineIf() / Trace.WriteLineIf()• Debug.Assert() / Trace.Assert()• using System.Diagnostics;• You can set number of hits and hit condition

for breakpoints– Just right-click on the red dot of the breakpoint

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Error Handling (try..catch..finally)

• While running a program through the IDE (i.e. during the development step, or Debug mode), you receive an error message if an error occurs.

• However, if your program runs in the final version (or Release mode), an error causes your program to terminate.

• For these cases, you may prefer using structured exception handling (or try..catch..finally)

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Sections of the try Structure

• try: The try section is where you place code that might cause an exception.

• catch: Code within the catch section executes only when an exception occurs.

• finally: Code within the finally section occurs when the code within the try and/or catch sections completes. This section is where you place your cleanup code—code that you always want executed, regardless of whether an exception occurs.

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try Example

int number = int.Parse(Console.ReadLine());int result = 100 / number;string str = result.ToString();

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An error may occur while converting a

text into an integer!

An error may occur if the number is

zero!

try Example – Solution 1

try{ int number = int.Parse(Console.ReadLine()); int result = 100 / number; string str = result.ToString();} catch { Console.WriteLine(“An error has occurred!”);}

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try Example – Solution 2try{ int number = int.Parse(Console.ReadLine()); int result = 100 / number; string str = result.ToString();} catch (ArgumentException ex1){ Console.WriteLine(“An ArgumentException error occurred!”);} catch (DivideByZeroException ex2) { Console.WriteLine(“The divisor can’t be zero”);} catch (Exception ex) { Console.WriteLine(“An unspecified error occurred. The details is: ” +

ex.Message);}

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try Example – Solution 3

int result = 0;string strResult;try{ int number = int.Parse(Console.ReadLine()); result = 100 / number;} catch (Exception ex) { Console.WriteLine(“An unspecified error occurred. The details is: ” +

ex.Message);} finally { strResult = result.ToString();}

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try Example on Database Operations

try{ … // Open database … // Make some operations on the database} catch { … // Error handling statements} finally { … // Close the database}

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