Re:Initialization in C++ is Seriously Bonkers
by MaxBarraclough on Sunday January 06, 2019 @05:50AM
(#18837691)
First up, I think I was technically mistaken in saying the blog was technically mistaken. It seems the language spec defines the UB in terms of read-before-assignment, but they do use the term 'indeterminate value' as well. So the blog post can be seen as incomplete, rather than mistaken.
> Undefined behavior in the technical sense is not acceptable in a language at all
The C committee disagrees, and they have their reasons. They're aiming to maximise performance and support for various weird and wonderful platforms.
C's philosophy is not like that of Java where, say, an int is defined to be 32 bit and your machine just has to make it happen, even if it's a peculiar 48 bit machine or something.
> If you take the idea of undefined behavior seriously, then it is valid to blow up the world in response to an error and the compiler cannot protect you
Well sure. UB means you screwed up. C isn't a hand-holding language. Explode the whole process. Perfectly valid. Not without precedent in the C++ spec, incidentally; C++ is defined to explode your process if you screw up in a certain way with exceptions https://stackoverflow.com/a/43675980/
Your program can't literally blow up the world, of course, but that's beyond the scope of the language. If UB could result in nuclear apocalypse, that would mean a compiler bug could generate a binary that did the same thing, regardless of source language.
> Nobody would use C or C++ if they actually accepted the meaning of undefined behavior, so to program in these languages requires embracing doublethink.
Plenty of C/C++ programmers have a very sloppy attitude to undefined behaviour, and sometimes they get bitten by it. Aggressive optimising compilers like gcc, really do depend on you taking responsibility for writing code with defined behaviour. Break that contract, and you can see nightmare intermittent bugs that only appear when using certain compiler flags. See: http://blog.llvm.org/2011/05/what-every-c-programmer-should-...
Of course, this is all made worse by that it's impossible for static analysis to detect all instances of UB. If you want a language that doesn't take this attitude, you might try Ada. It's a pity more people don't.
> Undefined behavior in the technical sense is not acceptable in a language at all
The C committee disagrees, and they have their reasons. They're aiming to maximise performance and support for various weird and wonderful platforms.
C's philosophy is not like that of Java where, say, an int is defined to be 32 bit and your machine just has to make it happen, even if it's a peculiar 48 bit machine or something.
> If you take the idea of undefined behavior seriously, then it is valid to blow up the world in response to an error and the compiler cannot protect you
Well sure. UB means you screwed up. C isn't a hand-holding language. Explode the whole process. Perfectly valid. Not without precedent in the C++ spec, incidentally; C++ is defined to explode your process if you screw up in a certain way with exceptions https://stackoverflow.com/a/43675980/
Your program can't literally blow up the world, of course, but that's beyond the scope of the language. If UB could result in nuclear apocalypse, that would mean a compiler bug could generate a binary that did the same thing, regardless of source language.
> Nobody would use C or C++ if they actually accepted the meaning of undefined behavior, so to program in these languages requires embracing doublethink.
Plenty of C/C++ programmers have a very sloppy attitude to undefined behaviour, and sometimes they get bitten by it. Aggressive optimising compilers like gcc, really do depend on you taking responsibility for writing code with defined behaviour. Break that contract, and you can see nightmare intermittent bugs that only appear when using certain compiler flags. See: http://blog.llvm.org/2011/05/what-every-c-programmer-should-...
Of course, this is all made worse by that it's impossible for static analysis to detect all instances of UB. If you want a language that doesn't take this attitude, you might try Ada. It's a pity more people don't.