Comment by tialaramex
18 hours ago
The entire I/O streams (where std::cout comes from) feature is garbage, if this was an independent development there is no way that WG21 would have taken it, the reason it's in C++ 98 and thus still here today is that it's Bjarne's baby. The reason not to take it is that it's contradictory to the "Don't use operator overloading for unrelated operations" core idea. Bjarne will insist that "actually" these operators somehow always meant streaming I/O but his evidence is basically the same library feature he's trying to justify. No other language does this, and it's not because they can't it's because it was a bad idea when it was created, it was still a bad idea in 1998, the only difference today is that C++ has a replacement.
The modern fmt-inspired std::print and std::println etc. are much nicer, preserving all the type checking but losing terrible ideas like stored format state, and localisation by default. The biggest problem is that today C++ doesn't have a way to implement this for your own types easily, Barry illustrates a comfortable way this could work in C++ 26 via reflection which on that issue closes the gap with Rust's #[derive(Debug)].
Remember that C++ originally didn't have variadic templates, so something like std::format would have been impossible back in the day. Back in the day, std::iostream was a very neat solution for type safe string formatting. As you conceded, it also makes it very easy to integrate your own types. It was a big improvement over printf(). Historic perspective is everything.
> The biggest problem is that today C++ doesn't have a way to implement this for your own types easily
I’m not sure about the stdlib version, but with fmtlib you can easily implement formatters for your own types. https://fmt.dev/11.0/api/#formatting-user-defined-types
I think the problem is that your idea of "easy" is "Here's a whole bunch of C++ you could write by hand for each type" while the comparison was very literally #[derive(Debug)]. I wasn't abbreviating or referring to something else, that's literally what Rust programmers type to indicate that their type should have the obvious boilerplate implementation for this feature, in most types you're deriving other traits already, so the extra work is literally typing out the word Debug.
> The entire I/O streams (where std::cout comes from) feature is garbage, if this was an independent development there is no way that WG21 would have taken it, the reason it's in C++ 98 and thus still here today is that it's Bjarne's baby.
I think this is a very lazy and somewhat conspiratorial take.
C++'s IO stream library, along with C++'s adoption of std::string, is a response to and improvement over C's standard library support for IO. That alone makes it an invaluable improvement. It's easy and very lazy to look back 30 years ago and badmouth things done back then.
It's also easy to complain about no one proposing changes when literally anyone, including you, can propose changes. The only need to do the legwork and put their money where their mouth is. The funny part is that we see frameworks putting together their own IO infrastructure and it ends up being not good, such as Qt's take on IO.
But talk is cheap and badmouthing doesn't require a pull request.
> Don't use operator overloading for unrelated operations
This disn't stop with <iostream>, they keep doing it - the latest example I can think of is std::ranges operations being "piped" with |.
Perfectly iostreams happy user since 1993.
int a;
cin >> a;
Then the program goes berserk as soon as the first non-number is read out of standard input. All the other "cin >> integer" lines are immediately skipped.
Yes, I know about error checking, clearing error condition, discarding characters. But it's a whole lot of stuff you need to do after every single "cin>>" line. It makes the simplicity of cin not worth it.
the program goes beserk as soon as the first non-number is read out of standard input.
in both cases, you need error checking (which you "know about").
1 reply →
How could you ever continue after the second statement without checking if you actually read an integer or not? How would you know what you can do with a?
2 replies →
You’re holding it wrong. Like nan, the point is you don’t have to error check every operation.
You check error for the whole batch.
Same, as long as I stay the hell away from locales/facets.
Type safe input/output stream types and memory backed streams served on a silver plate is a pretty decent improvement over C.
This was a tip my hatn excellent to you
Then I suppose you don't care about:
* Performance
* Support for localization (as the format string and positions of values to format differ between languages).
* Code reuse & dogfooding - the data structures used in iostreams are not used elsewhere, and vice-versa
* C and OS interoperability - as you can't wrap a stream around a FILE* / file descritor
* bunch of other stuff...
iostreams work, but are rather crappy.
I care about performance, when it actually matters to acceptance testing.
The less C the merrier.
If you care about correct use of localisation, standard C and C++ libraries aren't really what you're looking for, or even C and C++ to start with.
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Why?
Yep, it’s very clean once you get the hang of it.
Over the years, I have heard numerous complaints about C++ I/O streams. Is there a better open source replacement? Or do you recommend to use C functions for I/O?
>No other language does this, and it's not because they can't it's because it was a bad idea when it was created, it was still a bad idea in 1998, the only difference today is that C++ has a replacement.
Hindsight is 20/20, remember that. Streams are not that bad of an idea and have been working fine for decades. You haven't named a problem with it other than the fact the operators are used for other stuff in other contexts. But operator overloading is a feature of C++ so most operators, even the comma operator, can be something other than what you expect.
>The biggest problem is that today C++ doesn't have a way to implement this for your own types easily, Barry illustrates a comfortable way this could work in C++ 26 via reflection which on that issue closes the gap with Rust's #[derive(Debug)].
You can trivially implement input and output for your own types with streams.
You appear to be a Rust guy whose motive is to throw shade on C++ for things that are utterly banal and subjective issues.
What they mean is this:
with no extra code. It's called reflection, where the compiler can generate good-enough code to generate a character-stream serialization of an object without any human intervention.
I know what reflection is of course. C++ makes it easy to implement IO. If you're asking for a reflection-based solution with less effort, you are practically asking for zero extra code. Anyway, C++ does not yet have reflection but who's to say how anyone wants any particular data to be dumped? A default implementation is nice but less useful than you make it sound. In any case, there are libraries approximating what you described (usually with macros and stuff) and reflection is totally coming at some point.
What’s wrong with it?
Thank you.