Re: typedef float float4[4]; std::vector<float4>; does not compile, why?

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Tue, 19 May 2009 00:36:34 +0200

Message-ID:

<guso1d$290$1@news.eternal-september.org>

* Brian Cole:

The following code will not compile in gcc 4.3.2 on Ubuntu 8.10

#include <vector>

typedef float float4[4];

int main()
{
std::vector<float4> vals;
}

I get the following compilation error:
/usr/include/c++/4.3/bits/stl_construct.h: In function ?void
std::_Destroy(_Tp*) [with _Tp = float [4]]?:
/usr/include/c++/4.3/bits/stl_construct.h:103: instantiated from
?void
std::_Destroy(_ForwardIterator, _ForwardIterator) [with
_ForwardIterator =
float (*)[4]]?
/usr/include/c++/4.3/bits/stl_construct.h:128: instantiated from
?void
std::_Destroy(_ForwardIterator, _ForwardIterator,
std::allocator<_T2>&) [with
_ForwardIterator = float (*)[4], _Tp = float [4]]?
/usr/include/c++/4.3/bits/stl_vector.h:300: instantiated from
?std::vector<_Tp, _Alloc>::~vector() [with _Tp = float [4], _Alloc =
std::allocator<float [4]>]?
test_float4.cpp:7: instantiated from here
/usr/include/c++/4.3/bits/stl_construct.h:88: error: request for
member ?~float
[4]? in ?* __pointer?, which is of non-class type ?float [4]?

The code does compile in gcc 3.4 and gcc 4.1. So I'm guessing this is
because of some "enlightened" understanding of the C++ standard?
Please enlighten me.

The element type of a standard container must be copyable.

A raw array isn't.

Curiously, the code above compiles with Comeau Online, which appears to be a bug
in Comeau (considering that it aims to catch most errors).

Try this:

<code>
#include <vector>

typedef float float4[4];

int main()
{
   std::vector<float4> vals;
   float4 v = {};
   vals.push_back( v );
}
</code>

It should not compile.

Cheers & hth.,

- Alf

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