how do u convert a vector<float> A to a vector<double> B

[bluekite2000]

and why doesnt the standard vector have such conversion available?

[Ali Çehreli]

<bl**********@gmail.com> wrote in message
news:11**********************@o13g2000cwo.googlegr oups.com...

and why doesnt the standard vector have such conversion available?

You can use the vector constructor that takes two iterators:

#include <vector>
#include <assert.h>

using namespace std;

int main()
{
vector<float> a;
a.push_back(1.2f);

vector<double> b(a.begin(), a.end());

assert(!b.empty());
cout << b.front() << '\n';
}

Ali

[Mike Wahler]

> Re: how do u convert a vector<float> A to a vector<double> B

std::vector<float> A;
/* etc */
std::vector<double> B(A.begin(), A.end())

<bl**********@gmail.com> wrote in message
news:11**********************@o13g2000cwo.googlegr oups.com...

and why doesnt the standard vector have such conversion available?

It does. See above.

-Mike

[bluekite2000]

What if b is already constructed?
Another question
Say you have
vector<float> a(3);
//init a
vector<std::complex<float> > c(3);
//init c
Now I want something like
real(c)=a;

Currently I have
for(int i=0;i<c.size();i++)
c[i].real()=a[i];

Which I dont really like.

[Ali Çehreli]

<bl**********@gmail.com> wrote in message
news:11**********************@o13g2000cwo.googlegr oups.com...

What if b is already constructed?
Then it's assignment:

b = vector<double>(a.begin(), a.end());
Another question
Say you have
vector<float> a(3);
//init a
vector<std::complex<float> > c(3);
//init c
Now I want something like
real(c)=a;

Currently I have
for(int i=0;i<c.size();i++)
c[i].real()=a[i];

Which I dont really like.

There is nothing wrong with it. Just wrap it in a function and you are done:

typedef vector<float> Reals;
typedef vector<complex<float> > Complexes;

void set_reals(Complexes & complexes, Reals const & reals)
{
// some checks
if (complexes.size() != reals.size())
{
throw SomeError;
}

/* the logic here */
}

Very neat :)

More cool (and possibly more obscure) things can probably be done, but I
really don't think that it's worth it.

Ali

[Ivan Vecerina]

"Ali Çehreli" <ac******@yahoo.com> wrote in message
news:df**********@domitilla.aioe.org...

<bl**********@gmail.com> wrote in message
news:11**********************@o13g2000cwo.googlegr oups.com...

What if b is already constructed?

Then it's assignment:

b = vector<double>(a.begin(), a.end());

Actually, a probably better expression (for clarity,
maintainability, and performance) is:

b.assign( a.begin(), a.end() );
hth, Ivan
--
http://ivan.vecerina.com/contact/?subject=NG_POST <- email contact form
Brainbench MVP for C++ <> http://www.brainbench.com

[Clark S. Cox III]

On 2005-08-31 18:14:04 -0400, bl**********@gmail.com said:

and why doesnt the standard vector have such conversion available?

#include <vector>
#include <algorithm> //for std::copy

....

std::vector<float> A = ...;

//Construct B with the contents of A
std::vector<double> B(A.begin(), A.end());

//Or if B is already constructed:
B.clear();
B.insert(B.begin(), A.begin(), A.end());

//Or:
B.resize(A.size());
std::copy(A.begin(), A.end(), B.begin());
--
Clark S. Cox, III
cl*******@gmail.com

[Clark S. Cox III]

On 2005-09-01 00:09:55 -0400, "Ivan Vecerina"
<IN*************************@vecerina.com> said:

"Ali Çehreli" <ac******@yahoo.com> wrote in message
news:df**********@domitilla.aioe.org...

<bl**********@gmail.com> wrote in message
news:11**********************@o13g2000cwo.googlegr oups.com...

What if b is already constructed?

Then it's assignment:

b = vector<double>(a.begin(), a.end());

Actually, a probably better expression (for clarity,
maintainability, and performance) is:

b.assign( a.begin(), a.end() );

There is no "assign" function on std::vector.
--
Clark S. Cox, III
cl*******@gmail.com

[Marc Mutz]

Clark S. Cox III wrote:
<snip>

Actually, a probably better expression (for clarity,
maintainability, and performance) is:

b.assign( a.begin(), a.end() );

There is no "assign" function on std::vector.

23.2.4.1 vectors constructors, copy, and assignment
<snip>
template <class InputIterator>
void assign(InputIterator first, InputIterator last);

Effects:
erase(begin(), end());
insert(begin(), first, last);

template <class Size, class U> void assign(Size n, const U& u = U());

Effects:
erase(begin(), end());
insert(begin(), n, t);
<snip>

Maybe your compiler lacks member template support?

Marc

[Marc Mutz]

Clark S. Cox III wrote:
<snip>

//Or:
B.resize(A.size());
std::copy(A.begin(), A.end(), B.begin());

b.clear();
b.reserve( a.size() );
std::copy( a.begin(), a.end(), std::back_inserter( b ) );

Marc

[Clark S. Cox III]

On 2005-09-01 08:52:49 -0400, Marc Mutz
<ma**@klaralvdalens-datakonsult.se> said:

Clark S. Cox III wrote:
<snip>

Actually, a probably better expression (for clarity,
maintainability, and performance) is:

b.assign( a.begin(), a.end() );

There is no "assign" function on std::vector.

23.2.4.1 vectors constructors, copy, and assignment
<snip>
template <class InputIterator>
void assign(InputIterator first, InputIterator last);

Effects:
erase(begin(), end());
insert(begin(), first, last);

template <class Size, class U> void assign(Size n, const U& u = U());

Effects:
erase(begin(), end());
insert(begin(), n, t);
<snip>

Maybe your compiler lacks member template support?

Well, I'll be. I can't believe I missed that.

I think I was looking at the first listing in 23.2.4 without
remembering the "Descriptions are provided here only for operations on
vector that are not described in one of these tables or for operations
where there is additional semantic information." part.
--
Clark S. Cox, III
cl*******@gmail.com