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I have a class I've written, meant to represent vectors (in the linear algebra sense). I just started writing it so it isn't finished, but i've pasted it and some test code here

I'm not really sure what's going on. I was going to write an overloaded operator<< for testing in a second, so I went ahead and put it in my main function (so I could use compiler errors to make sure I'd written it properly).

What does this warning mean? why it is looking at the address of v? I tried removing the parentheses from v, and I end up with this, a bunch of horrible template errors: `

In function 'typename boost::range_const_iterator<C>::type boost::range_detail::boost_range_begin(const C&) [with C = vect<float, 3u>]':
/usr/local/include/boost/range/begin.hpp:164:   instantiated from 'typename boost::range_const_iterator<C>::type boost::begin(const T&) [with T = vect<float, 3u>]'
prelude/more_stdlib_ostreaming.hpp:64:   instantiated from 'void more_stdlib_ostreaming_detail::print_range(std::basic_ostream<_CharT, _Traits>&, const Range&) [with C = char, Tr = std::char_traits<char>, Range = vect<float, 3u>]'
prelude/more_stdlib_ostreaming.hpp:76:   instantiated from 'typename more_stdlib_ostreaming_detail::snd<typename R::iterator, std::basic_ostream<_CharT, _Traits>&>::type operator<<(std::basic_ostream<_CharT, _Traits>&, const R&) [with C = char, Tr = std::char_traits<char>, R = vect3f]'
t.cpp:42:   instantiated from here
Line 45: error: 'const class vect<float, 3u>' has no member named 'begin'`

I can sort of see whats going on here, tho. It looks like it is somehow using boost's range for and trying to iterate over my container, and it is failing because I haven't defined begin() and end(). The same thing happens if I instantiate v using v(some_float) rather than without the parens.

So, two questions:

  1. Why is v() behaving differently than v? I thought that declaring a object without parens always calls the default ctor anyway, and explicitly calling the default ctor made no difference?

  2. What is codepad's compiler (gcc 4.1.2) doing here? Does it have a template that automatically tries to generate an appropriate operator<

Also, feel free to tell me anything else I'm doing stupid/wrong/bad style here (besides rolling my own matrix math library for fun, which I know is unnecessary. I'm doing it as an exercise)

MSalters
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Alexander Questioning Bresee
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1 Answers1

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First of all, vect3f v(); declares a function (named v), taking no parameters and returning vect3f. And the operator<< that is being called is called for this function pointer (which is implicitly converted to bool, because there's no overload for function pointers).

vect3f v; is the correct way of creating default-constructed object.

And no, compiler won't try to generate ostream& operator<<(ostream& /* ... */) for you. There are however many overloads for all fundamental types and even some other types (such as std::string).

You can check all basic overloads here.

Vitus
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  • Thanks, you answered my first question. But the second question remains in the air. I edited the question to add the error I was worried about -- can you tell me whats going on there? – Alexander Questioning Bresee Apr 11 '11 at 21:30
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    That must be some kind of black magic going on codepad's part (you never included anything from boost libraries, yet is it showing in error message). My gcc (4.5.0 and 4.6.0) provides pretty clear error message: `error: no match for 'operator<<' in 'std::cout << v'` (and then lists tons of candidates). – Vitus Apr 11 '11 at 21:41