Re: [TUHS] speaking of early C compilers

Casts were invented as part of the port of Unix to the 32-bit Interdata. The early Unix system manuals actually printed the structure declarations for things like directory inodes in the manual -- there were no header files. This meant a massive amount of work when we wanted to use different structures for the 32-bit system. To make matters worse, many system calls returned -1 as an error indication, and on the Interdata loading an integer from location -1 gave an unrecoverable machine fault (!). As a final blow, the lack of type checking between pointers and structure members made it very hard to catch old code at compile time. The cast syntax, arguably one of the ickiest parts of C syntax, was invented in desperation -- we needed the feature, and there was no good syntax proposal. I blush to admit that the one Dennis chose is one that I suggested, largely because (unlike some of the others) it was easy to implement in Yacc. We hacked a version of Lint to force structures whose physical declaration locations were different to appear to be different structures, even if they were identical. Then, as header files were introduced, we could find all the user-level structure declarations that were copied from the man pages and fix them. This was extremely valuable, and allowed a summer intern from Princeton to convert most of the user-level programs to V7 in a summer. As an aside, one of the hairiest pieces of code I ever wrote was the part of PCC that handled structure declarations--it had to understand the "old style anything goes" syntax, but if the compiler decided that there was some attempt to use the new semantics, it changed modes and retroactively complained about possible type mismatches. The code was festooned with assertions, most of which were very short (memory being precious) -- one or two words like "junk" or "garbage". When compiling the V7 file system, Ken managed to totally confound my code by declaring a structure that had an array whose dimension was computed using a sizeof of another structure declared inside of the sizeof. He came to me one afternoon with a strange expression on his face and asked "Hey Steve, what is a gummy structure?"...