[verall]

What's wrong with std::regex? Seems to work fine for me.

And iostreams - they're not great. Bad programming UI, poor performance, etc. Issues abound. But should you never use them? What do you use instead? *printf methods have lots of issues too. And so does depending on Boost::format. And so does writing your own Logger/wrapping code (which is what everyone does AFAICT).

locale is bad though

[_eojb]

Well, `std::regex` is literally orders of magnitude slower than other common regex libraries found in JS, Python, Perl, C, etc. It allocates a ton, is poorly implemented, and can never be fixed due to ABI constraints. The entire <regex> subsystem is a mess and should have never been standardized as is.

[johannes1234321]

While that is true it can still be a good thing to use on a non-perofrmance critical path instead of adding a dependency on an external library.

Maybe it shouldn't be there and some better thing should be there, but given it exists ... as long as one is aware of alternatives using it is fine.

[ninepoints]

There's "not fast but usable enough" of course, but I would never ship std::regex code on any user facing software. Forget realtime, std::regex fails to be interactive in examples where other libraries resolve quickly.

[TylerGlaiel]

the last time I tried it (it was years ago) std::regex was taking a measurable number of milliseconds to evaluate which is kind of a very long time even outside of performance critical paths.

[otabdeveloper4]

There's nothing wrong with the std::regex design as it is the standard.

std::regex only sucks because the developers of gcc and clang never bothered to optimize it. (Too much work and they have other stuff to worry about.)

[JonChesterfield]

"can't be fixed without breaking ABI" sounds plausible for C++.

There's generally not all that much stdc++ specific optimisation stuff in clang. There might be parts of regex that are worth implementing as compiler intrinsics, that seems to be the existing pattern for making bits much faster.

The really heavy lifting you want for regex is to partially evaluate and split them. They're a separate language unto themselves and benefit from being optimised as such. There's nowhere ideal in the clang/llvm pipeline to do that though.

[otabdeveloper4]

C++ regexes are literally just copy-pasted ECMAScript regexes. They could have just used an existing regex library, but C++ compiler developers presumably don't want to support an extra dependency.

That's the only real reason why std::regex is slow.

[leni536]

std::regex also depends on locale, which is reason enough to avoid it, regardless of performance.

[npsimons]

> What do you use instead [of std::iostream]?

This is what I want to know. Having come from C to C++, iostreams were a big improvement over the "strings" and print functions of C. I even extended a base iostream class to have a "teebuf" logger, that could output to multiple streams and had the standard logging levels.

It's been a while since I last had mastery of C++, but I'd like to hear what is as portable and better than iostreams.

[dietrichepp]

Strings in C++ are nice, especially now that we have std::string_view, but <iostream> is one of the worst pieces of the C++ standard library.

- <iostream> makes localization more difficult, compared to printf (localizing <iostream> code is beyond awful)

- <iostream> makes thread safety more difficult, compared to printf (it is safe to printf/fprintf from multiple threads, simultaneously, without any extra work)

- The <iostream> operator overloading syntax is bad (my sense is that the operator overloading abuse in <iostream> was a contributing factor for why Java doesn't allow operator overloading)

- Streams in <iostream> are stateful, and it's easy to accidentally leave them in the wrong state (radix, padding, field width, etc)

- Performance of <iostream>, out of the box, is mediocre (to get decent performance, you need to change some defaults)

The main advantage of <iostream> was that it provided type safety, but IMO that advantage has long since been irrelevant. You get type safety with std::printf, with most compilers, assuming you enable -Wformat on GCC or similar options in other compilers.

The only remaining advantage of <iostream> is that you can overload operator<<. I don't think that's much of an advantage, especially weighed against the numerous disadvantages.

Using std::printf is better and more portable. Libfmt is also better and more portable, and it is now part of the standard library as std::format.

https://www.moria.us/articles/iostream-is-hopelessly-broken/

[offices]

>The <iostream> operator overloading syntax is bad

In an obnoxious way. The first code someone will see of a new language is often 'hello world'. In C++, 'hello world' is an advertisement for the fact that operator overloading exists.

[NooneAtAll3]

I still don't get the hate for <<

it's the coolest part

[therein]

libfmt is definitely recommended.

About 6-7 years ago back when my employer was running code compiled with gcc-4.4.7 and running it on Linux 2.6.32 boxes even though it was pretty old even back then, it took me a lot of convincing the company to give libfmt a try.

It was such a boost to developer happiness. People were literally overjoyed, writing to me on Slack how much of a pleasure string formatting has become.

[usefulcat]

> I'd like to hear what is as portable and better than iostreams

Have a look at fmtlib. The interface is more like printf, but type safe and format strings are parsed at compile time. I believe it’s what std::format is based on, which could also be an option for you depending on how recent your compiler/language version is.

[npsimons]

> The interface is more like printf

See, I don't believe that's an improvement. Having used printf in C, I was relieved to be able to "redirect" whatever to a stream, and not care about whether it should be "%d" or "%02f" or even if it was a struct/class.

On top of this, treating files as streams, strings as streams, or even extending streams to make a tee-stream[0] all seem clunkier to me with a printf like system.

Maybe fmt fixes these problems, I don't know. But I feel a lot of people don't like iostreams because they have some form of Stockholm syndrome with printf.

[0] - https://wordaligned.org/articles/cpp-streambufs#tee-streams

[dietrichepp]

> Maybe fmt fixes these problems, I don't know.

Yeah, it looks like you did a lot of guesswork in that comment, and a lot of those guesses were inaccurate. Not really trying to be hostile here, but you did acknowledge that you were unfamiliar with std::format.

The part that fmtlib / std::format has, which is printf-like, is the idea of having a format string and arguments, rather than having a bunch of separate, piecemeal strings.

  // Old printf code, works ok for most people
  std::printf("failed to clone %s from %s", target, src);
  // <iostream>
  std::cout << "failed to clone " << target << " from " << src;
  // New std::format / fmtlib
  std::print("failed to clone {} from {}", target, src);

You can see that you don't need to remember what kind of format specifier you need. This is C++, and that kind of problem is solved with overloading.

The std::print interface can work equally well with FILE or std::ofstream, or whatever you want. This is C++, and so you can just use a templated output iterator—or one of the overloads that creates one automatically.

There are a lot of problems with <iostream>. I think it’s telling that lots of languages have copied printf, but nobody (or almost nobody) thought <iostream> was good enough to copy. There are just too many serious design flaws with <iostream>. It would be one thing if <iostream> were just annoying to use, but it poses problems for localization, thread-safety, accidental misuse through its statefulness, and its operator overloading syntax is bad.

[tialaramex]

> It would be one thing if <iostream> were just annoying to use, but it poses problems for localization, thread-safety, accidental misuse through its statefulness, and its operator overloading syntax is bad.

It's Bjarne (Stroustrup)'s pet feature. You'll notice that many expert practitioners of C++ write std::println("Hello, world"); or similar for a canonical C++ 23 Hello World, but Bjarne pointedly still writes it with std::cout and the iostream operator overloads.

Now that Bjarne is back at Columbia teaching, there's a risk he'll infect impressionable young people with this nonsense, COMSW4995 was not an intro class and I suspect Bjarne's jetsetting makes it impractical to teach such a class, so this risk is small but not zero.

[usefulcat]

fmtlib knows the types of all the arguments, and those types are checked against the format string at compile time. So type safety ("%d" vs "%s" etc) is not really an issue.

FWIW, I have waaaay more experience with iostreams than printf. I once wrote a replacement for most parts of std::ostream purely because I had a logging system that was loosely based on log4cxx (which is based on iostreams) and I needed much faster formatting.

Right now I'm in the process of switching to a different logging system that uses fmtlib. I can say that I really, really do not miss the extreme verbosity of iostreams at all. The statefulness I could take or leave, although on balance I'd say it's usually more of a negative. Thankfully I don't have to give up type safety or extensibility.

As for treating files/strings/whatever as streams--my impression of fmtlib is that it's concerned primarily with formatting, which frankly I'm fine with. It can write to an in-memory buffer or to a FILE* or to a std::ostream, which covers pretty much all of my needs. Given the performance of iostreams (lots of virtual method calls) I never really saw the point of using it as a more generalized 'streaming' interface, even knowing that it's possible.

[95014_refugee]

Considering the origins of "stockholm syndrome" this may not be exactly the message you intended.

However, printf and its ilk get it right; presentation is a property of the context in which the entity is to be presented, not of the entity itself. You can kvetch about the markup syntax, or the type safety issues the C implementation has, but the architecture is fundamentally correct.

[trws]

It’s impossible to implement std::regex efficiently due to internal but exposed character handling requirements. To the sibling comments about iostream, thank vzeverovich and everyone that worked on fmt and turning it into std::format (edit: accidentally wrote std::fmt initially), which is vastly superior and not dependent on mutable global state.

[einpoklum]

1. Historically, std::regex was offered in GCC before it was actually fully implemented. Much hilarity ensued...

2. Some existing implementations have efficiency issues, e.g. performing many allocations.

3. It is claimed (e.g. by Titus Winters) that the ABI of std::regex is problematic, and without breaking it, the implementations cannot be good enough

See these points and others at:

https://www.reddit.com/r/cpp/comments/e16s1m/what_is_wrong_w...

[plq]

> What's wrong with std::regex?

In my experience, stdlibc++ <regex> is VERY slow, especially on debug builds. We are using g_regex instead, which in turn uses pcre2.

> And iostreams

<iostream> achieves too little with too much code. We instead use:

    std::cout << fmt::format(...);

for simple output, loguru[1] for everything else. I feel like the fmt grammar/mini-language is both nicely extensible and has hit the expressiveness sweet spot -- not too verbose (iostreams) nor too terse (printf).

I also like that fmt has helpers for pointers (fmt::ptr), enums (fmt::underlying) and arrays (fmt::join). It's both easy on the eyes and feels consistent.

[1]: https://github.com/emilk/loguru

[fyrn_]

Consider ``` #include <fmt/os.h>

... fmt::print(...); ``` Instead, to save that potential double buffer copy.

[plq]

Thanks! Still learning my way around the fmt library.

[verall]

fmt looks really nice. Probably worth pulling the dependency in for future projects.

[tcbawo]

IMHO, the printf-style API is superior to the stream based API, because it can be adapted into a logging API that defers string formatting or delegates it to another thread. Overloading by type can be accomplished with printf-style API as well. Cluttering business code with string formatting can be a liability in code that needs to be performant/low latency, which is one of the primary reasons people use C++.

[gpderetta]

iostreams are not great but are nothing compared to the awkwardness and lack of extensibility of printf style format strings.

[scatters]

iostream is replaced by format.