I used to slay with this in code golfing competitions from TopCoder, where you had to implement a function to solve a particular problem, thanks to C pointer maths and the gcc generally putting function arguments in order in the stack.
Turns out, these two are equivalent in practice (but UB in the C++ standard):
double solve(double a, double b, double c, double d) {
return a + b + c + d;
}
double solve(double a ...) {
return a + 1[&a] + 2[&a] + 3[&a];
}
Not in the x86-64 SysV ABI they aren’t. The arguments will be passed in registers (yes, even the variadic ones), so how your compiler will interpret 1[&a] is anybody’s guess. (For me, x86_64-unknown-linux-gnu-g++ -O2 yields, essentially, return a+a+a+a; which is certainly an interpretation. I’m also getting strange results from i686-unknown-linux-gnu-g++ -O2, but my x87 assembly is rusty enough that I don’t really get what’s going on there.)
The cast in the invocation can be macro-ed away. And the best thing is, the actual stack layout and data movement/shuffling is pretty much identical to the approach with <stdargs.h>, and with no UB or compiler intrinsics.
This seems pretty good to me just on the level of trying to read C as someone using C++. Parameter packs and variadic templates are easily the most confusing syntax in C++ and cleaning it up is... very welcome
You can always restrict yourself to a subset of C++ that takes advantage of RAII (resource handling is extremely painful in C), and get performance benefits like move semantics, without the insanely complex stuff.
I love C, but C++ has worthwhile advantages even if you heavily restrict which features you use.
Of course since the old syntax is merely deprecated and not removed, going forward you now have to know the old, bad form and the new, good form in order to read code. Backwards compatibility is a strength but also a one-way complexity ratchet.
I think Rust has shown a way to remove deprecated interfaces while retaining back compat - automated tooling to migrate to the next version and give a few versions for a deprecated interfaces to stick around at the source level.
Regular variadic arguments in general aren't used very often in C++ with exception of printf like functions. Not rare enough for majority of C++ programmers to not know about them, but definitely much more rare than their use in python. Main reason people know about it at all is printf.
The "new" C compatible form has been supported since the first ISO standardized version of c++ if not longer. There haven't been a good reason to use the "old" form for a very long time. Which means that the amount of C++ code using deprecated form is very low.
Being deprecated means that most compilers and linters will likely add a warning/code fix suggestion. So any maintained project which was accidentally using C incompatible form will quickly fix it. No good reason not to.
As for the projects which for some reason are targeting ancient pre ISO standard c++ version they wouldn't have upgraded to newer standard anyway. So if new standard removed old form completely it wouldn't have helped with those projects.
So no you don't need to know the old form to read C++ code. And in the very unlikely case you encounter it, the way for accessing variadic arguments is the same for both forms through special va_list/va_arg calls. So if you only know the "new" form you should have a pretty good idea of whats going on there. You might lookup in references what's the deal with missing coma, but other than that it shouldn't be a major problem for reading code. This is hardly going to be the biggest obstacle when dealing with code bases that old.
The “new” form has been valid since the original 1998 C++ standard, where it was added for compatibility with C. “You now have to know” has therefore already been the case for the past 27 years. Back then the old pre-standard form was kept for backwards compatibility, and is only now being deprecated.
The old-style variadics are rarely seen in C++ these days, never mind this particular edge case. If you working in a vaguely modern version of C++ this largely won’t impact you. You can almost certainly ignore this and you’ll be fine.
Unless you have a massive legacy code base that is never updated, C++ has become much simpler over time. At a lot companies we made a point of slowly re-factoring old code to a more recent C++ standard (often a couple versions behind the bleeding edge) and it always made the code base smaller, safer, and more maintainable. It wasn’t much work to do this either.
C++ seems to be constantly getting complicated. If the major version were to change, there wouldn't be any need for backward compatibility with the existing code, and it would have been okay to delete that syntax while creating an automatic formatter.
I mean this is extremely minor, but the more incompatibility you create the slower the uptake will be. In the extreme you could create a Python 2->3 situation over old syntax.
Yes, but no. I learned C++ in '90s when it was C with classes and some other noise added by Stroustrup. During the some 25 years that followed it had became a mess that's insanely hard to work with. I'm not going back to this language. I prefer plain C or Rust, leaning towards Rust when I fully comprehend the lifetime and borrow checker. Or when I have the luxury of having a GCed runtime, then the .NET with its easiest C# language with wonderful abundance of great libraries is the best choice. Nobody was ever fired for using .NET (for right purposes).
Tiring how often this needs to be said, but if you want "C with classes", you can just use C++ that way.
I've been using C++ for more than 30 years (I added thread_local to Cfront back in the early 90s), and while the language has grown dramatically in that time, there is fundamentally nothing that would prevent me from writing "C with classes" using the modern version.
I don't do that because I also like RAII, and polymorphism, and operator overloading and ...
I've never used .NET and could not imagine any scenario under which I would. The libraries that matter to me are mostly written in C or C++ and there are more of them than I'd ever need, mostly.
This is a good change. Potentially ambiguous to read syntax is being made clearer in a way that harms no previous code substantially.
I sometimes wonder if the comments that say nothing more than "C++ is too complicated" are from people who use it regularly, much less people who are even commenting on TFA
25 comments
[ 3.5 ms ] story [ 58.3 ms ] threadTurns out, these two are equivalent in practice (but UB in the C++ standard):
Not in the x86-64 SysV ABI they aren’t. The arguments will be passed in registers (yes, even the variadic ones), so how your compiler will interpret 1[&a] is anybody’s guess. (For me, x86_64-unknown-linux-gnu-g++ -O2 yields, essentially, return a+a+a+a; which is certainly an interpretation. I’m also getting strange results from i686-unknown-linux-gnu-g++ -O2, but my x87 assembly is rusty enough that I don’t really get what’s going on there.)
Err no; https://gcc.godbolt.org/z/sW3ea58oc
They're equivalent on GCC.
I love C, but C++ has worthwhile advantages even if you heavily restrict which features you use.
At least they managed to kill `auto_ptr`.
Regular variadic arguments in general aren't used very often in C++ with exception of printf like functions. Not rare enough for majority of C++ programmers to not know about them, but definitely much more rare than their use in python. Main reason people know about it at all is printf. The "new" C compatible form has been supported since the first ISO standardized version of c++ if not longer. There haven't been a good reason to use the "old" form for a very long time. Which means that the amount of C++ code using deprecated form is very low.
Being deprecated means that most compilers and linters will likely add a warning/code fix suggestion. So any maintained project which was accidentally using C incompatible form will quickly fix it. No good reason not to.
As for the projects which for some reason are targeting ancient pre ISO standard c++ version they wouldn't have upgraded to newer standard anyway. So if new standard removed old form completely it wouldn't have helped with those projects.
So no you don't need to know the old form to read C++ code. And in the very unlikely case you encounter it, the way for accessing variadic arguments is the same for both forms through special va_list/va_arg calls. So if you only know the "new" form you should have a pretty good idea of whats going on there. You might lookup in references what's the deal with missing coma, but other than that it shouldn't be a major problem for reading code. This is hardly going to be the biggest obstacle when dealing with code bases that old.
Unless you have a massive legacy code base that is never updated, C++ has become much simpler over time. At a lot companies we made a point of slowly re-factoring old code to a more recent C++ standard (often a couple versions behind the bleeding edge) and it always made the code base smaller, safer, and more maintainable. It wasn’t much work to do this either.
To some extent with C++, complexity is a choice.
I have no idea where you get this idea from. I expect gcc v28 to be able to compile C++ from 2008, and I'm not alone in that.
I've been using C++ for more than 30 years (I added thread_local to Cfront back in the early 90s), and while the language has grown dramatically in that time, there is fundamentally nothing that would prevent me from writing "C with classes" using the modern version.
I don't do that because I also like RAII, and polymorphism, and operator overloading and ...
I've never used .NET and could not imagine any scenario under which I would. The libraries that matter to me are mostly written in C or C++ and there are more of them than I'd ever need, mostly.
I guess that's a preview how C++ require a lifelong commitment.
In my opinion anyway. C++ feels so bloated these days.
I sometimes wonder if the comments that say nothing more than "C++ is too complicated" are from people who use it regularly, much less people who are even commenting on TFA