Is there a way to cast from vector<unsigned> to vector<int>?

[Peng Yu]

Suppose that I have a variable of vector<unsigned>, and a function that takes an argument of const vector<int>&.

One thing to pass this variable to this function is to create a copy (with type vector<int>) of the variable, but this involes the extra copying.

Is there a way to somehow directly supply the variable to the function without using a copy?

Regards,
Peng

[Richard]

[Please do not mail me a copy of your followup]

Peng Yu <peng...@gmail.com> spake the secret code
<57513843-102e-4199...@googlegroups.com> thusly:

>Is there a way to somehow directly supply the variable to the function
>without using a copy?

No. An unsigned can hold positive integer values that don't fit into
an int.
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[Mr Flibble]

On 08/06/2015 04:58, Stefan Ram wrote:

> Peng Yu <peng...@gmail.com> writes:
>> Suppose that I have a variable of vector<unsigned>, and a
>> function that takes an argument of const vector<int>&.

>> Is there a way to somehow directly supply the variable to the
>> function without using a copy?
>

> You can cast the object, but this might mean that the cast
> or call will have undefined behaviour or in the best case
> will behave as if each unsigned was reinterpret as an int.
>
> Under some implementations this might be acceptable when all
> the unsigned objects have values that can be represented as
> an int.
>
> For example, one implementation gave:
>
> #include <iostream>
> #include <ostream>
> #include <vector>
> #include <climits>
>
> int main()
> { ::std::vector< unsigned >v{ 0, 1, INT_MAX,( unsigned )INT_MAX +( unsigned )1 };
> for( unsigned u : v )::std::cout << u << '\n';
> auto const &w( *reinterpret_cast< ::std::vector< int >* >( &v ) );
> for( int i : w )::std::cout << i << '\n'; }
>
> 0
> 1
> 2147483647
> 2147483648
> 0
> 1
> 2147483647
> -2147483648

You know it is UB yet you still suggest it? It is never acceptable to
deliberately invoke UB. Mate, I am sorry but if you wrote such code for
me you would be fired.

/Flibble