Learning C++

Debugging your Code

There are tens of debugging routines that can be used in C++, however, this section will only touch on the most easily accessible and the most useful ones that you might find yourself using.

Imagine you've just completed a project that you've been working on for a long time. You happily click on the Start button and run your application, however, the program doesn't run as expected. Calculations give wrong results and other options don't work. What would you do? Who you gonna call? Debug Mode, of course!

Debug Mode is essentially a mode that takes you through your code step by step. Therefore, you know what exactly happens to each of your variables and procedures. There are many options that VC++ gives you when debugging your code, however, this lesson will only show you the main features of this awesome and powerful feature in VC++.

There are three main types of errors that you can run into as a programmer: Syntax Errors, Run-Time Errors and Logic Errors. Syntax Errors happen when you mistype a command, for example, or write an incomplete structure. VB detects some of these Syntax Errors as you write the code. Run-Time Errors occur when VC++ tries carrying out an operation that is impossible, like dividing by zero or calling a non-existent file. The final type, Logical Errors, is a completely different story. Everything is compiled properly, with no messages from VC++, however, the code doesn't work as expected. This is because of flaws in the "logic" used in coding. The only way to fix this type of error is by testing and analyzing your code.

Breakpoints: This is something that you'll want to use a lot. Breakpoints are markers placed on lines in your code that cause your C++ compiler to pause as soon as it reaches lines with breakpoints. This gives you the option to look inside your code and check everything while the application is still active (To check values of variables, hover your mouse cursor over the desired variable). You can then run your program step by step and see exactly how every line executes.

To set a breakpoint, make sure you're in code view, click on the line where you want C++ to break and press F9. To remove it press F9 again. You should see a dark red dot on the left of the line. When you run your program and C++ breaks on that line, use the Debug toolbar to step into, out of or over lines of code. Many other options are also available on the Debug toolbar:

Debug Bar Mini Build Bar

Debug Bar
Button Name	Description
Restart	Restarts the current program.
Stop	Stops debugging the program.
Break Execution	Stops the program running and enters debug mode.
Apply Code Changes	If you make any changes to your code while in debug mode, then this will apply the changes to your program.
Show next statement	Shows the next statement in your program code. If source code is not available, displays the statement within the Disassembly window.
Step Into	Steps into the next statement (line of code).
Step Over	Steps over the next statement
Step Out	Steps out of the current function. Useful if you want to exit a loop.
Run to Cursor	Runs the program and then stops on the line containing the cursor. To set your cursor on a line, simply click on it.
QuickWatch Window	Display the value of any variable/expression in debug mode.
Watch Window	Shows/hides the Watch window. This allows you to select certain variables to watch. For example, you could set up the Watch window to break when a certain variable's value changes to a specific number.
Variables Watch	Shows/hides the Variables window. This shows you values of all variables that have been initialized so far.
Registers	Shows/hides the Registers window.
Memory	Shows/hides the Memory window.
Call stack	Shows/hides the Call stack window.
Disassembly	Shows/hides the Disassembly window.
Mini Build Bar
Button Name	Description
Compile	Compiles only the current file in the project.
Build	Compiles all files contained in the project.
Stop Build	Stops building the current program.
Execute	Compiles and runs your program.
Go	After inserting a breakpoint, this will run your program and then enter debug mode upon reaching a line containing a break point.
Toggle Breakpoint	Insert/remove a breakpoint.

The table should answer most of your questions. Basically to enter break mode and debug your code:

1. Set breakpoints.

2. Click on the Go button (F5).

3. When the program enters debug mode, use the buttons Step into, Step over and Step out to work your way through the code.

4. When you're done, click on the Stop Debug button.

If the Debug Tool Bar is not visible, right click on any blank space next to a toolbar and choose Debug from the popup menu.

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