constructing const vectors

[Dan Smithers]

Is there a way of specifying the contents of a vector in the constructor
when the elements are not identical?

I would like to be able to construct a static const vector that contains
pre-determined values.

class CFoo
{
static const std::vector<intm_foo;

static const int *const m_bar;
....
};

const std::vector<intCFoo::m_foo({1, 2, 3});
const int *const CFoo::m_bar = {10, 20, 30};

As I want a static member, it needs to be all done through the constructor.

Would it be easier just to declare a const array as in m_bar?

thanks

dan

[Lionel B]

On Fri, 02 May 2008 11:24:55 +0100, Dan Smithers wrote:

Is there a way of specifying the contents of a vector in the constructor
when the elements are not identical?

I would like to be able to construct a static const vector that contains
pre-determined values.

class CFoo
{
static const std::vector<intm_foo;

static const int *const m_bar;
...
};

const std::vector<intCFoo::m_foo({1, 2, 3});
const int *const CFoo::m_bar = {10, 20, 30};

As I want a static member, it needs to be all done through the
constructor.

std::vector has a constructor that takes a range (i.e. a first and last
iterator) as parameters. These iterators can be pointers, so I suppose
you could use that. Eg.:

#include<vector>

int main()
{
const int a[] = {10,20,30};
const int* const p = a;
const std::vector<intv(p,p+3);
}

works as expected.

Would it be easier just to declare a const array as in m_bar?

Only you know the answer to that.

--
Lionel B

[Christian Hackl]

Dan Smithers schrieb:

Is there a way of specifying the contents of a vector in the constructor
when the elements are not identical?

You could use the Boost Assignment library.

http://www.boost.org/doc/libs/1_35_0...doc/index.html

I would like to be able to construct a static const vector that contains
pre-determined values.

class CFoo
{
static const std::vector<intm_foo;

static const int *const m_bar;
...
};

const std::vector<intCFoo::m_foo({1, 2, 3});
const int *const CFoo::m_bar = {10, 20, 30};

const std::vector<intCFoo::m_foo(list_of(1)(2)(3));
--
Christian Hackl

[Lionel B]

On Fri, 02 May 2008 14:21:41 +0200, Christian Hackl wrote:

Dan Smithers schrieb:

>Is there a way of specifying the contents of a vector in the
constructor when the elements are not identical?

You could use the Boost Assignment library.

http://www.boost.org/doc/libs/1_35_0...doc/index.html

>I would like to be able to construct a static const vector that
contains pre-determined values.

class CFoo
{
static const std::vector<intm_foo;

static const int *const m_bar;
...
};

const std::vector<intCFoo::m_foo({1, 2, 3}); const int *const
CFoo::m_bar = {10, 20, 30};

const std::vector<intCFoo::m_foo(list_of(1)(2)(3));

error: call of overloaded ‘vector(boost::assign_detail::generic_list<int>& )’ is ambiguous

but:

const std::vector<intCFoo::m_foo = list_of(1)(2)(3);

seems ok. I don't understand why - I'd have thought they were equivalent.

--
Lionel B

[Rolf Magnus]

Lionel B wrote:

std::vector has a constructor that takes a range (i.e. a first and last
iterator) as parameters. These iterators can be pointers, so I suppose
you could use that. Eg.:

#include<vector>

int main()
{
const int a[] = {10,20,30};
const int* const p = a;
const std::vector<intv(p,p+3);
}

works as expected.

Or a bit simpler:

#include<vector>

int main()
{
const int a[] = {10,20,30};
const std::vector<intv(a, a + sizeof(a));
}

[=?ISO-8859-1?Q?Marcel_M=FCller?=]

Rolf Magnus schrieb:

Or a bit simpler:

#include<vector>

int main()
{
const int a[] = {10,20,30};
const std::vector<intv(a, a + sizeof(a));
}

That's wrong.

You wanted to write

const std::vector<intv(a, a + sizeof(a)/sizeof(*a));
Marcel

[James Kanze]

On May 2, 6:18 pm, Marcel Müller <[e-mail]:

Rolf Magnus schrieb:

Or a bit simpler:

#include<vector>

int main()
{
const int a[] = {10,20,30};
const std::vector<intv(a, a + sizeof(a));
}

That's wrong.

You wanted to write

const std::vector<intv(a, a + sizeof(a)/sizeof(*a));

Actually, what he probably wanted to write was:

std::vector< int const v( begin(a), end(a) ) ;

where begin() and end() are the usual thing that everyone pretty
much has in their toolkit:

template< typename T, size_t N >
T*
begin( T (&array)[ N ] )
{
return array ;
}

template< typename T, size_t N >
T*
end( T (&array)[ N ] )
{
return array + N ;
}

--
James Kanze (GABI Software) email:ja*********@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientierter Datenverarbeitung
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]

[Christian Hackl]

Lionel B wrote:

On Fri, 02 May 2008 14:21:41 +0200, Christian Hackl wrote:

>const std::vector<intCFoo::m_foo(list_of(1)(2)(3));

error: call of overloaded ‘vector(boost::assign_detail::generic_list<int>& )’ is ambiguous

but:

const std::vector<intCFoo::m_foo = list_of(1)(2)(3);

seems ok. I don't understand why - I'd have thought they were equivalent.

Well, they are not exactly equivalent. In the second version, a
temporary std::vector is constructed using list_of(1)(2)(3), and m_foo
is then initialised with that temporary using std::vector's copy
constructor.

So it seems to me that in this example, construction of said temporary
std::vector is necessary to make list_of work, and that the compiler
does not elide the copy constructor call (as it usually does) because
that would change the meaning of the code.

Someone care to shed some light on this issue? :)
--
Christian Hackl