Rules and Warnings
As with almost all things PL/SQL, external procedures come with an obligatory list of cautions:
· While the mode of each formal parameter (IN, IN OUT, OUT) may have certain restrictions in PL/SQL, C does not honor these modes. Differences between the PL/SQL parameter mode and the usage in the C module cannot be detected at compile time, and could also go undetected at runtime. The rules are what you would expect: don't assign values to IN parameters; don't read OUT parameters; always assign values to IN OUT and OUT parameters; always return a value of the appropriate datatype.
· Modifiable INDICATORs and LENGTHs are always passed by reference for IN OUT, OUT, and RETURN. Unmodifiable INDICATORs and LENGTHs are always passed by value unless you specify BY REFERENCE. However, even if you pass INDICATORs or LENGTHs for PL/SQL variables by reference, they are still read-only parameters.
· Although you can pass up to 128 parameters between PL/SQL and C, if any of them are float or double, your actual maximum will be lower. How much lower depends on the operating system.
· Because extproc might be a multithreaded process in future releases, and because the operating system won't ask permission before unloading shared libraries from memory, your external code should avoid the use of any internal or external "static" variables.
· Your external procedure may not perform DDL commands, begin or end a session, or control a transaction using COMMIT or ROLLBACK. (See Oracle's PL/SQL User's Guide and Reference for a complete list of unsupported OCI routines.)
Colophon
Our look is the result of reader comments, our own experimentation, and feedback from distribution channels. Distinctive covers complement our distinctive approach to technical topics, breathing personality and life into potentially dry subjects.
Ants are featured on the cover of Oracle PL /SQL Programming, Third Edition. At least 8,000 different species of ants can be found everywhere on Earth except the North and South Poles. Ants preserved in amber suggest that these insects existed 50 million years before humans.
Humans have long been fascinated by ants, because these tiny insects are accomplished builders, nurses, miners, and even farmers. Fables such as "The Ant and the Grasshopper" extol the virtues of hardworking, forward-looking ants. (Hail ants!) It is true that individual ants are able to perform amazing feats: an ant can carry up to 50 times its body weight, can travel the human equivalent of 40 miles a day, and can climb vertical heights the equivalent of Mount Everest. However, the greatest accomplishments of ants are those performed together for the good of their community.
Queen ants establish new communities, or nests, after their mating flight. On this flight the queen mates with several males. After mating, the males fall to Earth and die. The queen then finds an uninhabited nest, settles into it, and pulls her wings off. She will never fly again, and after removing her wings she is able to absorb the wing muscles as nutrients for her eggs. She will continue to lay eggs, thousands of them, for years.
During the three-stage development process, which takes about two months, the eggs, larvae, and pupae are cared for by the nurse ants, who feed, clean, and carefully move the young to warmer or cooler places in the nest, depending on the temperature. These nurse ants are, in turn, cared for by other worker ants, who feed the nurses with regurgitated food. The workers and the nurses will fight together to defend the young against enemies if the nest is invaded, either by another group of ants or by a larger animal.
Emily Quill was the production editor and copyeditor for Oracle PL/SQL Programming, Third Edition . Mary Anne Mayo, Sheryl Avruch, Matt Hutchinson, and Jane Ellin provided quality control. Phil Dangler, Derek DiMatteo, and Kimo Carter provided production assistance. Ellen Troutman wrote the index.
Edie Freedman designed the cover of this book. The cover image is a 19th-century engraving from the Dover Pictorial Archive. Emma Colby produced the cover layout with QuarkXPress 4.1 using Adobe's ITC Garamond font.
David Futato designed the interior layout. This book was converted to FrameMaker 5.5.6 with a format conversion tool created by Erik Ray, Jason McIntosh, Neil Walls, and Mike Sierra that uses Perl and XML technologies. The text font is Linotype Birka; the heading font is Adobe Myriad Condensed; and the code font is LucasFont's TheSans Mono Condensed. The illustrations that appear in the book were produced by Robert Romano and Jessamyn Read using Macromedia FreeHand 9 and Adobe Photoshop 6. The tip and warning icons were drawn by Christopher Bing. This colophon was written by Clairemarie Fisher O'Leary.
The online edition of this book was created by the Safari production group (John Chodacki, Becki Maisch, and Madeleine Newell) using a set of Frame-to-XML conversion and cleanup tools written and maintained by Erik Ray, Benn Salter, John Chodacki, and Jeff Liggett.