MySQL Cookbook, 2nd Edition

Checking for Errors

Problem

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

Solution

Everyone 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 that your programs can help you figure out what went wrong.

Discussion

After working through Connecting, Selecting a Database, and Disconnecting, 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 specific error information from the API, so that’s what we’ll cover next. You’re probably anxious to see how to do more interesting things (such as issuing statements and getting 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.

When errors occur, MySQL provides three values:

• A MySQL-specific error number

• A MySQL-specific descriptive text error message

• An SQLSTATE error code that is a five-character value defined according to the ANSI and ODBC standards

Various sections in this recipe in this section show how to access this information. Most of the later recipes in this book that display error information print only the MySQL-specific values, but the recipes here show how to access the SQLSTATE value as well, for those APIs that expose it.

The example programs demonstrate how to check for errors ...