CS2604 Programming Tools

Memwatch

Memwatch is a small module that replaces the standard C++ operators new and delete with versions that add extra debugging features. Adding Memwatch to your program project won't cure problems, but it will add extra memory checking that will sometimes detect and report existing problems so oyu can fix them. Problems detected include:

• Memory leaks--memory that is allocated but never released.
• Memory overwrites and underwrites--when you access memory just outside the bounds of what you have allocated, like accessing elements just off either end of an array.
• Multiple deletes--when the same block of memory is deallocated more than once, leading to corruption of the heap.

There are three files you can download:

• The two Memwatch files:
  • Memwatch.h
  • Memwatch.cpp
• Main.cpp--a trivial program that demonstrates how to use Memwatch.

To use Memwatch, follow these simple steps:

• Add Memwatch.cpp to your C++ project.
• Add '#include "Memwatch.h"' to all .cpp files in your project.
• Compile and run your program.
• Examine the log file "memwatch.log" produced in the current directory after running the program. Each time Memwatch uncovers an error, it reports the available diagnostic information to this file.

Warning Regarding Free Lists!

Under Microsoft Visual C++ Memwatch.h redefines "new" to be a macro in order to work with VC++'s debugging runtime library. This means it may cause strange compiler errors or warnings if you are defining your own overloaded new/delete operators to maintain free lists for your ADTs.

If this is the case but you still want to use Memwatch, simply place "#ifdef _DEBUG ... #endif" around the lines of code in your .h and .cpp files where you define your operator new and operator delete code. This will allow Memwatch to work correctly.

By selecting the "Debug" or "Release" configuration of your project when compiling, you can control whether or not your own personal free list code is included (it will only be in the "Release" configuration with the above #ifdef). Memwatch will work under either configuration, but returns more detailed information in the "Debug" configuration.

This version of Memwatch was modified locally by Dr. Edwards to work with Microsoft Visual C++ in standard console-mode applications. If you are working with MFC GUI applications, use the MFC memory debugging settings described below.

Microsoft's MFC Memory Diagnostics

If you are using Microsoft Visual C++, you can use Microsoft's own memory debugging code build into the debugging version of its C++ runtime code. Microsoft has designed its memory aid to work with MFC applications, but it can also be used with plain old console-mode Win32 applications.

Microsoft's memory diagnostic features are described under the DEBUG_NEW macro in the MFC documentation. To use them in a regular program, do the following:

• In each .cpp file, add '#include <afx.h>' at the top.
• Edit your configuration settings (choose "Settings..." from the "Build" menu). Select the "C/C++" tab. Under the "Category" drop down list, select "Code Generation". In the "Use run-time library" drop down list, select "Debug Multithreaded".
• Run the program. Any memory diagnostic messages (including a list of leaked memory chunks) will appear under the "Debug" tab of the messages/output window.

Check Microsoft's on-line books for "DEBUG_NEW" or "diagnostics" for more information on what you can do when this memory tracking support is enabled. DEBUG_NEW is primarily for spotting memory leaks, so it does not provide as much checking as Memwatch. It is a useful tool, however.