Running a small part of the programYou may not need to use CodeView to find bugs in simple programs. For more complex programs, however, using CodeView can save you debugging time and effort.
When you debug with CodeView, you usually cycle between two activities:
Running a small part of the program
Stopping the program to check its status
You use breakpoints to switch between these tasks. CodeView runs your program until it reaches a breakpoint. At that time, CodeView gives you control. You can then enter CodeView commands in the Command window or use the menus and shortcut keys to proceed.
To find an error, try the following:
Set breakpoints around the place you think the bug might be. Execute the program with the Go command so that it runs at full speed until it reaches the area that you suspect harbors the bug. You can then execute the program step by step with the Program Step and Trace commands to see if there is a program execution error.
Set breakpoints when certain conditions become true. You can, for example, set a breakpoint to check a range of memory starting at DS:00, the base of your program's data. If your program writes to memory using a null pointer, the breakpoint is taken, and you can see what statement or variables within the statement are in error.
Watch expressions constantly display the values of variables in the Watch window. By setting a Watch expression, you can see how a variable or an expression changes as your program executes.
Try using watch expressions as follows:
Set a Watch expression on an important variable. Then step through a part of the program where you suspect there is a bug. When you see a variable in the Watch window take on an unexpected value, you know that there is probably a bug in the line you just executed.
Explore Watch expressions. A bug can appear when your program builds complex data structures. Both the Watch window and the Quick Watch dialog box allow you to explore the data structure by expanding arrays and pointers. Use this feature to make sure the program creates the data structure correctly. As soon as you execute code that destroys the structure, you have probably found a bug.
Your display can be more effective if you arrange your windows so that they display the information you need. You will need at least one Source window. You can open a second Source window to see each assembly-language instruction.
You may also need one or more Memory windows to examine ranges of memory in various formats. You may want to change values in memory. For example, a program that does its own dynamic-memory allocation may need an initialized block of memory. You can edit memory directly in the Memory window or fill the block with zeros using the Memory Fill command. If a certain value is required for a mathematical function, you can type over values displayed in the Memory window or assign the value in the Command window. If you expect a value to appear at a certain location and it does not, you can use the Memory Search command to find it.
Use the Register window to see the CPU registers and the Local and Watch windows to keep track of changing variable values. Open the Calls menu to examine your program's stack to see what routines have been called.
You can set up CodeView's windows to display the information you want to see by using keyboard commands or the commands in the Window menu. For example, when you press SHIFT+F5 or choose Tile from the Windows menu, CodeView arranges all open windows to fill the entire window area. When the windows are tiled, you can press ALT+F5 or choose Arrange from the Windows menu. This allows you to move your open windows with a mouse so that you can view several or all of them at once.