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Comment by simoncion | Hacker News Reader

> How is iostream any better than [<star>]printf?

What consistent mechanism do you use to printf an instance of an arbitrary user-defined type?

With ostream, you implement

  ostream& operator<<(ostream&, const Class&)

and you're done.

with printf, you have to have a convention and remember to stick to it. (Do I call .toString(), .stringize(), .getString()... ??)

For one-off things, printf is great. You take it from me when you pry it from my goddamn cold, dead, hands. However, for real work io*stream are rather nice.

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With printf, you do have to look at the docs to see what the string conversion function is. With iostream, you still have to look at the docs to see if the ostream operator is implemented for the class, it's certainly not universal.

I never said io*stream support was universal, [0] I said that it provided a _consistent_ mechanism. :)

[0] I mean, it's obvious that anything that you don't get for free out of the box is bound to _not_ be universal. Edit: Actually, the thing you get out of the box when you present an instance of a non-trivial user-defined class to both printf and ostream is equally useless... unless you're debugging and are interested in the address of the instance of an object.

Right, I'm just questioning whether this consistency buys you anything. Either way you're checking the docs to see how to print an object.

> ...I'm just questioning whether this consistency buys you anything.

It buys you the same thing that API consistency always buys you: reduced cognitive overhead when dealing with a given API. :)

Edit: As GFK_of_xmaspast mentions [0] instances of non-trivial classes are not compatible with the default implementations of "operator <<" in ostream. So, you can try "ostream << instanceOfNonTrivial". If it passes the compiler, then you know that operator << is defined for that class.

So, no need to check the docs... just ask the compiler. :)

[0] https://news.ycombinator.com/item?id=10775022

> look at the docs to see if the ostream operator is implemented for the class

Or give it a go and see if the ide/compiler complains.

It has been so long that that bit of information had dropped out of my brain. I went to verify, and -obviously- there is no auto-conversion for instances of a non-trivial class.

Thanks for reminding me of this. Kudos!

I find that how I print my data changes depending on why I'm printing, making a convention necessary anyways. Is the ostream overload the user-visible format, the test-failure format, or the serialization format?

noob question - what is the use case for a program that operates on arbitrary user defined types? Dynamic typing sounds lazy and slow in my head, might as well use python at this point

> ...what is the use case for a program that operates on arbitrary user defined types?

That's not what's going on. Neither C nor C++ really permits that.

We're just talking about the relative merits of using printf and friends vs. using iostream to format data for the console or disk.

In either case, you have to write the code for your class that massages the class's internals correctly, but the question is, do you write to the ostream extraction and istream insertion API, or do you write to the substantially less well defined printf-and-friends API?

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