MySQL Cookbook

Checking for Errors

Problem

Something went wrong with your program and you don’t know what.

Solution

Everybody has problems getting programs to work correctly. But if you don’t anticipate difficulties by checking for errors, you make the job a lot harder. Add some error-checking code so your programs can help you figure out what went wrong.

Discussion

You now know how to connect to the MySQL server. It’s also a good idea to know how to check for errors and how to retrieve MySQL-related error information from the API, so that’s what we’ll cover next. When errors occur, MySQL provides a numeric error code and a corresponding descriptive text error message. The recipes in this section show how to access this information. You’re probably anxious to see how to do more interesting things (such as issue queries and get back the results), but error checking is fundamentally important. Programs sometimes fail, especially during development, and if you don’t know how to determine why failures occur, you’ll be flying blind.

The example programs in this section show how to check for errors, but will in fact execute without any problems if your MySQL account is set up properly. Thus, you may have to modify the examples slightly to force errors to occur so that the error-handling statements are triggered. For example, you can change a connection-establishment call to supply a bad password. This will give you a feel for how the code acts when errors do occur.

A general debugging aid that is not specific ...