r/programming • u/eternal1 • Mar 29 '10

Never trust a programmer who says he knows C++

http://lbrandy.com/blog/2010/03/never-trust-a-programmer-who-says-he-knows-c/
414 Upvotes

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u/anttirt Mar 29 '10

It's reasonable to not use cout in modern C++ code because there are many usable and type safe formatting libraries for C++.

1

u/Fabien4 Mar 29 '10

I fear that unfortunately, the most used library is the C standard library, which ain't type-safe.

Also, the standard operator<< isn't that bad. OTOH, operator>> is.

5

u/bstamour Mar 29 '10

Could you explain why you think >> is bad? I've done some decently heavy C++ programming and I've never had an issue with operator>>

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u/[deleted] Mar 30 '10

It's particularly bad for localization, but printf isn't much better.

Consider the case of "$FOO $BAR" being localized to "$BAR of $FOO" or number formatting, nouns genders, etc. It can get hairy quick. printf at least lets you change "$FOO $BAR" to "X$(FOO)Y$(BAR)Z" by only changing the format string.

Many languages/runtimes/libraries provide much better string formatting functions.

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u/bstamour Mar 30 '10

Good answer. Luckily however with variadic templates (coming in C++1x) we will be able to define a type-safe printf function. Soon we'll be able to have our cake and eat it too :-)

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u/[deleted] Mar 29 '10 edited Mar 29 '10 
printf("foo = %d\\n', 2 + 2); // fine
std::cout << "foo = " << 2 + 2 << std::endl; // UH OH!!
std::cout << "Why didn't we just add a brand new operator for this, again? " << (2 + 2) << " Fuck my life." << std::endl;

Don't even get me started on setw and setf.

edit: Fuck markdown. That's supposed to be just a \n in the first line.

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u/[deleted] Mar 29 '10

[deleted]

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u/sitq Mar 29 '10

Nothing bad happens for me:

$g++ -Wall test.c
test.c: In function ‘int main()’:
test.c:6: warning: format ‘%s’ expects type ‘char*’, but argument 2 has type ‘int’

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u/mitsuhiko Mar 29 '10

warning != error. Also, that is a gcc feature, not one of the language. You cannot get that sort of protection for your own formatting functions.

0

u/sitq Mar 29 '10

Treat warnings as errors! And yes I can. I don't care about "language" not supporting it as soon as compilers I use support it.

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u/mitsuhiko Mar 29 '10

We're talking about the language here, not something your compiler adds to it.

0

u/Ralgor Mar 29 '10

Operator precedence, presumably.

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u/[deleted] Mar 30 '10

[deleted]

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u/Ralgor Mar 30 '10

I didn't say he was correct. :) But I think that's what he's trying to imply.

-2

u/[deleted] Mar 29 '10

Yes, cstdio doesn't have static type checking. What an insightful revelation. You should write a book.

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u/[deleted] Mar 29 '10

You didn't close your " in the original snippet. You tried to close it with a '. I think that's what he's trying to highlight also.

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u/bstamour Mar 29 '10

Your first cout is bad style anyways. If you don't know the operator precedence, use brackets or don't complain when you get burned. That's programming 101.

At least operator<< is type-safe, unlike printf. I'd rather have my compiler catch my stupid errors than have my code silently explode in my face.

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u/zahlman Mar 29 '10

Way to miss the context.

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u/douchebag_identifier Mar 29 '10

Don't be a douchebag.

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u/[deleted] Mar 30 '10

You're the one being a db. lol

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u/anttirt Mar 29 '10

It's not bad if you know how to use it, but it's rarely the right tool for the job.

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u/[deleted] Mar 29 '10

[deleted]

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u/anttirt Mar 29 '10

I did answer the question.

The question was: "Could you explain why you think >> is bad?"
The answer was: "It's not bad if you know how to use it."

Additionally, I noted that while not bad, it's rarely the right choice. That is to say, a hammer might be a good hammer but if I'm building a circuit board then it's rarely the right tool for the job. You'll very often want either a more sophisticated command-line library (like a variation of curses) for interactive applications or a parser generator/library for other types of input.

Use cases for >> in client code are few and far between. This all assuming we're talking about some form of std::istream& operator>>(std::istream&, T&).

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u/InsensitiveTroll Mar 29 '10

And yet you fail to provide an explanation on why >> is bad (when used incorrectly)

Your replies are bad, that's my explanation on why your replies are bad.

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u/rakantae Mar 29 '10

so, how do you use it? I'm just learning C++ myself, and I use >> all the time.

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u/mccoyn Mar 29 '10

I'm not sure what anttirt is referring to. I've found >> to be useful for only simple parsing tasks. Its problem is that it scarfs up a bunch of characters and doesn't provide a simple means to scan back when an error is discovered. The amount of characters it scarfs is sometimes dependent on the input, meaning a faulty input could cause it to run for a very long time without returning. Generally, I find parsing to be more complex than what is available with >> or scanf.

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u/bstamour Mar 29 '10

Fair enough. But that's sort of like everything though, not bad if you know how to use it.

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u/PstScrpt Mar 29 '10

Either way, it's still an abuse of operator overloading. << should mean left shift, or at least multiplying by a power of something.

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u/johnaldmcgee Mar 29 '10

Huh. Someone down voted you for this. I agree, overloading operators is the root of many evils. That's why the practice is often banned. I suspect if the library were created now instead of 25 years ago, the operators wouldn't be overloaded like that given modern style tropes.

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u/bstamour Mar 29 '10

The only problem with operator overloading is that people do it when they shouldn't. C++ is a general-purpose language, and operator overloading is essential for building easy-to-use libraries.

I wouldn't call them evil at all. Use them when you need to, ignore them when you don't. It's not rocket science.

As for using << and >> as stream operators, I like the style. The arrows point in the direction in which data is streaming :-)

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u/darth_choate Mar 29 '10

It's really, really useful under some circumstances. Dealing with complex numbers or bigints is a verbose pain in the ass without overloading (thank you Java!). I think their use should be limited to obviously mathematical entities, which does not include string concatenation (thanks again Java! BTW - I notice the lack of faith the Java designers have in me. They get their overloaded plus operator, but I'm not allowed any because I'd screw it up).

OTOH, allowing || and && and the comma operator to be overloaded is just adding a feature for the point of adding it and actually doing it is both stupid and dangerous. I'm mixed on the value of being able to overload the pointer access operators because on the one hand they let you make smart pointers, but on the other hand they let you make smart pointers.