[i-am-curious]

> I don't see modern application of C outside embedded,

C is one of the most popular languages for high-performance code. Most famous example would be the Linux kernel but literally anything that needs the best optimizations possible eventually comes down to C.

[hellofunk]

Strange thing to say, to be honest. Many of the most performance-critical industries are heavy on C++, not C. Games, finance, high-frequency trading, where every microsecond is worth huge money -- these are typically C++ shops. The strictness and ability to move things to compile time are features not available in C.

[jstimpfle]

Any examples of using compile time features that make a difference, instead of making code harder to maintian and increasing compile times significantly?

[hellofunk]

You’re talking about really two different issues here. I don’t think anyone would suggest templates can’t get complicated. But they are certainly the doorway into maximum performance over C.

[jstimpfle]

No I don't think I'm talking about something else. And I wouldn't submit to the opinion that performance cricitical code needs to be written in C++.

For example, Games are heavy in C++ where there are a lot of abstractions. Engine code is mostly C style as far as I can tell. Optimized code is code that exploits specific properties of systems, hence it is significantly less abstracted than higher-level code.

The stereotypical std::sort example doesn't count, really. There are many reasons why std::sort vs qsort (which are both generic sorting implementations - i.e. not optimized ones) is not significant in practice, but it's still among the most frequently cited examples - hinting that there might be few real wins (with regards to performance) from all this compile time and templates stuff.

[hellofunk]

Hm, I’m not sure where to start with your assessment here. Your comments on sorting don’t really seem relevant, I don’t think you’re referring to the same kind of compile time programming we’ve been discussing. There’s a difference between generic code, and code that runs at compile time, even though both might actually use the C++ feature of templates. C++ templates are way to write code that supports generics, but they are also a way to do a style of programming referred to as “meta-programming“, these are really not the same thing at all.

While you can certainly do without generics in the language, as proven by the success of many many languages, perhaps at the inconvenience of some developers, compile time meta programming is an entirely different area that only few languages really support. The high frequency trading firms and the game studios I have partnered with are typically using C++ specifically for those compile time programming features. They make dramatic performance differences in a wide range of highly specialized algorithms.

[jstimpfle]

It wasn't me who said "templates" first. (I don't think of them as a practical way to do compile time computation).

I was mostly looking at constexpr and whatever similar things have appeared in C++ lately. And I wanted to know about actual applications of them in the wild that make a difference.

Because, yeah I can precompute a 100K hash table or whatever at compile time, but I can also just do it at program startup (would anyone notice?) which is by far the simplest thing to do. Or I could just generate the data in a separate build step which is probably more hassle compared to constexpr but also probably friendlier in terms of build times in practice.

[Nginx487]

I worked under ULL trading platform, they used C++ with heavy templates, without RTTI and exceptions. If things can be done in compile time, it should be done - which is the purpose of templates. Neither our nor neighbor teams (near 800 developers) used plain C. As Bjarne Stroustrup told, there's no place between C++ and machine code for "more low-level language", everything which could be done in C, also could be done in C++ with the same efficiency.

Good tendency however, now both C and C++ developers started experimenting with Rust, probably creating unified community and platform.

[harry8]

The problem is the one you state.

You have to use a subset of c++. Nobody agrees what that subset is. You have to be super-vigilant in code review. Features invite their use.

It's the lack of features in c that make it attractive. No magic. You want an object or a virtual, code it up if you really mean it is not just a keyword. You take responsibility for all the code running.

Every time I've cut a tonne of latency from a trading engine it's that. People relying on library and compiler without taking responsibility for it. STL is great. Except if you're actually performance critical, when you can beat it easily by solving your problem, not someone else's solution for everyone's possible similar problem.

[mehrdadn]

With the caveat that I am NOT suggesting this justifies choosing C over C++, I just wanted to mention this talk about how "zero-cost abstraction" is an idealism, not necessarily a reality: https://www.youtube.com/watch?v=rHIkrotSwcc&t=17m30s

That said, I tried to reproduce something similar, and it seems the issue only occurs in my example due to external linkage (adding 'static' fixes it)... but I can't claim this will always resolve the issue: https://gcc.godbolt.org/z/1vbqo3

[bregma]

The "zero-cost abstraction" concept is that you don't pay for something you don't use. If you use a smart pointer, you pay for it. If you don't use a smart pointer, it's zero cost.

Any argument that smart pointers are not zero cost to the language because they have a cost when you use them is a classic straw man argument.

[mehrdadn]

I think there might be a terminology mixup here but he probably meant zero-overhead abstraction. And in any case, the point he's making is not a strawman argument.

[bregma]

OK, let's substitute "overhead" for "cost in the argument.

Premise one: C++ has zero overhead for most of its features, like smarts pointers: if you don't use them, they cost nothing.

Premise two: using features like smart pointers adds a cost to your C++ program.

Conclusion (due to the strawman logical fallacy): C++ is not zero overhead because there exists a feature that has a cost if you use it.

I'd like to see the reasoning that leads to the same conclusion without resorting to the strawman logical fallacy.

[mehrdadn]

He talked about more than just unique_ptr if you actually watch the video, but I don't even get why you're dying to have such a pointless argument here. When you see free lunches offered somewhere, do you start arguing with people how everyone is wrong and there is such a thing as a free lunch too? Is it so hard to actually take the point and just move on instead of dissecting it like a mathematical theorem?

[virgilp]

I watched only a tiny part of that talk but the speaker claims "there are no zero-cost abstractions" and justifies it with.... unique-ptr??? I mean, who doesn't know that smart pointers can be slower than raw pointers? They're not there because they're "zero-cost", but because the improvement in reliability & readability more than makes up for the runtime cost in the vast majority of situations.

[mehrdadn]

He's comparing unique_ptr to just plain old-fashioned new and delete. Is it obvious to you what the actual cost is in moving between these? It's not really obvious and probably not what you think. I would listen to the full section of the talk on unique_ptr.

[virgilp]

I developed an optimizing C++ compiler in my youth (one that was actually used in production, not just a pet project). I probably know the actual cost, and also know it may depend on compiler.

But that's not the point - the point is that smart pointers never claimed to be zero-cost abstractions, AFAIK.

[mehrdadn]

> But that's not the point - the point is that smart pointers never claimed to be zero-cost abstractions, AFAIK.

> I mean, who doesn't know that smart pointers can be slower than raw pointers?

Nobody... on what basis? If you're not in that set of people, that doesn't imply the set is small or empty. Googling suggests lots of people have given such advice, and, may I suggest, it's not because they were stupid.

[pizza234]

What's your judgment on the Doom 3 source code? It's something performance critical, but it's in C++; Sanglard's review of the design codebase was very positive.

[clktmr]

John Carmack wrote in 2010: > There is some decent code in Doom Classic, but it is all C, and I would prefer to do new game development in (restrained) C++.

> I had been harboring some suspicions that our big codebases might benefit from the application of some more of the various �modern� C++ design patterns, despite seeing other large game codebases suffer under them. I have since recanted that suspicion.

I think this shows that C++ works better in controlled (i.e. corporate environments), whereas C is often preferred in Open Source.

[ricattierger]

Why do you say that? Certain things in a language may increase binary size or something else but at the end of the day these languages all go through most likely the same compiler and should produce a roughly equivalent binary.

[bregma]

They will produce equivalent binaries, but not identical binaries.

For example, GCC's C++ front end will produce a different parse tree for the same C code as the C front end, resulting in a slightly different collection of basic blocks and data flow analysis (obviously, for very trivial examples, it will be identical). The result after all the gimplification and and different middle-end passes and rtl transformations you can end up with a surprisingly different set of generated instructions for the same code fed to gcc and g++. Equivalent, but different.

[account42]

Nitpick: gcc and g++ are not different frontends but different compiler drivers. They can both invoke the C and C++ frontends (cc1 and cc1plus) and select them based on the file extension unless specified using the -x option. The difference between gcc and g++ is mainly in which libraries are linked by default.

[bregma]

Well, it's true that the different compilers are cc1 and cc1plus, but given most programmers I've run into here in vacuumland have trouble distinguishing between their IDE and their toolchain, expecting them to understand the difference between the actual compiler invoked by the driver depending on a file extension or '-x' switch vs. the different compiler driver that invokes that compiler by default for a given file extension is a bit of a stretch. Even you seem to be confused by the compiler proper (cc1 or cc1plus) and the front end (the part of each compiler that parses the code and builds an internal representation that then gets passed on to the middle end for optimization and the back end for register allocation and instruction generation).

The fact is, the front ends of cc1 and cc1plus will interpret the exact same C code differently to the extent that code containing undefined behaviour will have remarkably different results in the generated instructions. The differences between the cc1 and the cc1plus compilers are not limited to what the compiler driver passes to the linker, they have completely different front ends and only share the middle and back ends.

[account42]

> Even you seem to be confused by the compiler proper (cc1 or cc1plus) and the front end (the part of each compiler that parses the code and builds an internal representation that then gets passed on to the middle end for optimization and the back end for register allocation and instruction generation).

Sure, the cc1 and cc1plus binaries come with a middle and backend linked in, but what differentiates them is the front end. Not so much for gcc and g++ where both `gcc file.cpp` and `g++ file.cpp` will invoke cc1plus. Not to mention that with LTO cc1 and cc1plus do almost exclusively front end work while everything else happens in lto1 (for both C and C++).

[hellofunk]

> these languages all go through most likely the same compiler and should produce a roughly equivalent binary

That's not really true. A single compiler may support many languages but that does not mean code written in those languages ends up as the same binary.

[rvz]

Yet the 'modern web browsers' we're all using are probably written in C++.

I'm yet to see a 'modern web browser' that is fully written and only written in C. (C bindings don't count)

[harry8]

Original cross-platform Netscape was iirc. Quality died when they went to c++? Probably less influential on their fate than Microsoft.

[jcelerier]

> Quality died when they went to c++?

when they went to c++ it became Firefox. do you think we'd have a better firefox today had it stayed in C ?

[harry8]

/When/ they went, which, iirc was Netscape 4 (?). It was horrendous, crashing, slow buggy, awfulness, which the previous version really wasn't. This was when it was all closed and proprietary.

Firefox came a long time later. Well after Mozilla opened.

No idea if Firefox would be better if they'd stayed in c. What i do know is that c++ is a vastly, vastly better language now through no fault of the standards committee. G++ got good. Then came clang++, valgrind was an amazing leap forward too.

Before all that there really was no such thing as cross platform c++.