Building the whole Debian archive with GCC 4.1: a summary [LWN.net]

Building the whole Debian archive with GCC 4.1: a summary

Posted Mar 29, 2006 5:22 UTC (Wed) by butlerm (subscriber, #13312)
In reply to: Building the whole Debian archive with GCC 4.1: a summary by foo-bar
Parent article: Building the whole Debian archive with GCC 4.1: a summary

This is not something that just accidentally happened to work. The ISO C++ standard was not released until 1998. C++ had a 15 year history prior to that, and taking the offset of a class member was universally portable prior to that time.

But somehow, perhaps in a fit of Java envy, the ISO C++ folks decided that the C++ language should define an virtual abstraction far removed from its origins as a system programming language, and forbade perfectly well defined behavior. Not just declared the result to be "undefined" as sane standards bodies are wont to do, but forbade its use outright, breaking a large body of existing code.

And as one might expect, there is now speculation that the next version of the ISO C++ standard will remove this ridiculously pointless restriction.

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Building the whole Debian archive with GCC 4.1: a summary

Posted Mar 29, 2006 14:19 UTC (Wed) by butlerm (subscriber, #13312) [Link]

I should substitute "let the construct suffer in benign neglect" for "declare the result to be undefined". GCC has added an option (-Wno-invalid-offset-of) that eliminates the need for class data member offset gymnastics as well.

Building the whole Debian archive with GCC 4.1: a summary

Posted Mar 29, 2006 18:33 UTC (Wed) by JoeBuck (subscriber, #2330) [Link]

As you say, the ISO standard came out in 1998 (it was actually complete in December 1997, and only details have changed since draft standards put out in 1996). You've had more than eight years to fix your code.

Unfortunately, g++ 2.x accepted all kinds of bizarre stuff, and broke on all kinds of standard C++. The GCC developers made the decision to follow the standard. Unfortunately, too many folks in FLOSS-land never used any compiler other than g++, and never cracked a book on C++, so they just threw stuff at the compiler and accepted whatever the compiler let through. That was never a wise strategy.

C++ is the most complex of the widely used languages, and is hard to get right. Generally speaking, GCC has done very well, considering the massively difficult challenges.

There are a few cases where I would agree that GCC 4.1 is a bit too anal-retentive. However, for most of the cases that affect Debian code this is not the issue: if the compiler does not properly enforce the namespace rules, valid C++ programs break (because of name collisions or selecting the wrong overloaded function), and the only way to fix the breakage is to make changes that cause invalid programs that used to compile, to stop working.