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under Visual Studio .NET 2005. These warnings, number C4996, indicate that the older low-level methods have been replaced with newer implementations. Fortunately, the older methods are still available and the system will compile and run correctly. You can always turn off these warnings in the project settings.

To debug the server, I have to launch the server in debug mode. On Windows, you should use the switch to run the server stand-alone so that it doesn t run as a service. While this isn t strictly necessary, it allows you to see any messages from the server in the command window that would otherwise be suppressed. You can issue the following command to accomplish this: mysqld-debug --debug --standalone

Once the server is running, I can attach to the process from Visual Studio using the Debug Attach to Process menu selection. Figure 5-9 shows the Attach to Process dialog box. I choose to run and attach to the mysqld-debug process so that I can also generate a trace file during the debugging session.

Figure 5-9. Attaching to a process in Visual Studio .NET The next thing I need to do is launch the client. I once again use the connect-timeout parameter to set the timeout to a longer delay. The command I use to launch the client from a command window is mysql -uroot -p --connect-timeout=600 With the client running, I can issue the show authors; command, which Visual Studio will intercept when the breakpoint is encountered. I can then use the step over (F10) and step into (F11) commands to step through the code. I stop the code inside the loop, which sends data, and inspect the authors structure. Figure 5-10 shows the state of the debugger after I have stepped into the loop.

Figure 5-10. Displaying variable values in Visual Studio .NET As with ddd, you can also change values of variables. However, doing so in Visual Studio is a bit more complicated. While there may be other options, the best way to change values in Visual Studio is to edit the values in the watch window. However, if the values in the watch window are pointers to memory locations, you have to change the memory location. Do this by opening the memory debug window and use the watch window to locate the memory location and edit it in place. Figure 5-11 shows the memory window open and the values edited.

Figure 5-11. Editing values in memory using Visual Studio .NET After the values in memory are edited, I can continue the execution and see the results in the client window. Listing 5-17 shows an excerpt of the sample output. Listing 5-17. Output of Debugging Session mysql> show authors; +----------------+-----------------------+---------------------------------------+ | Name | Location | Comment | +----------------+-----------------------+---------------------------------------+ | Jane Doe | Anytown, USA | Really nice person. | ... +----------------+-----------------------+---------------------------------------+ 74 rows in set (1 min 55.64 sec) mysql>

To stop the debugging session, I issue the shutdown command in a command window and then detach from the process using the Debug Detach All menu selection in Visual Studio. mysqladmin -uroot -p shutdown Now that you ve seen how to debug the MySQL system using Visual Studio on Windows, I encourage you to read through this example again and try it out on your own Windows development machine.

Summary

In this chapter, I explained debugging, showed you some basic debugging techniques, and provided examples of how to use them. These techniques include inline debugging statements, error handling, and external debuggers. You learned how to use the inline debugging statements DBUG tool provided by MySQL AB to create trace files of the system execution, write out pertinent data, and record errors and warnings. You also learned about debugging in Linux and Windows using gdb, ddd, and Visual Studio .NET. Developing good debugging skills is essential to becoming a good software developer. I hope that this chapter has provided you with a foundation for perfecting your own debugging skills. In the next chapter, I ll examine one of the popular uses of the MySQL system by system integrators: embedded MySQL. This permits the MySQL system to become a part of another system. As you can imagine, the process could require some serious debugging to figure out what went wrong at what level of the embedding.