[krylon]

A couple of years back, I ran into a nasty problem with structure packing that made me get acquainted with structure padding and packing.

The company I was working at used the OpenWatcom compiler that lets you tune structure padding with a compiler flag. Also, they "serialized" their data by simply writing arrays of structs to files and reading them back in later. Raw binary files, no conversion whatsoever.

So one day - I hadn't been there very long - I was given the task to make a certain change to the application, as well as a copy of a "database" to experiment on. I made a first adjustment, compiled my code, ran it and - BAM! It took me nearly a day to figure out that I had "forgotten" to pass a certain variable to make which in turn resulted in a certain parameter being passed to the Watcom compiler that caused it to use no structure padding at all.

Without that variable/parameter, I had compiled the program to use a different padding (i.e. use padding at all), so when my program read the data file (having been dumped by a version of the program being compiled without padding), it barfed, so to speak.

That problem caused me to do a little reading on the matter. I sure wish somebody had pointed that article out to me back then. (Assuming it had existed back then, with "back then" being about October 2007.)