Re: Using for each, in with STL containers with non-const iterators

From:

"freak" <farid.mehrabi@gmail.com>

Newsgroups:

microsoft.public.vc.stl

Date:

5 Feb 2007 08:33:34 -0800

Message-ID:

<1170693213.990496.31050@p10g2000cwp.googlegroups.com>

On Jan 31, 6:58 pm, Wyck <W...@discussions.microsoft.com> wrote:

I want to use the "for each, in" syntax with an STL container, and still
modify the elements of the container while iterating.

I was expecting this to work:

std::vector<int> lst;
lst.push_back(1);
lst.push_back(2);
lst.push_back(3);
for each( int& num in lst ) {
num++;

}

But it gives the error:
'static_cast' : cannot convert from 'const int' to 'int &'

Why is it using a const iterator when i'm using a reference type? Is there
a way to do this?

This is valid code:
for each( const int& cref in lst ) { /**/ }

...but 'cref' is not an l-value, so you can't modify the elements of the
list while iterating!

And this is valid code:
for each( int clone in lst ) { /**/ }

...but 'clone' is a copy of the element, not the original. Any changes to
'clone' are not reflected in the original 'lst' array elements.

To work around I would write it using traditional syntax:
for( std::vector<int>::iterator i=lst.begin(); i!=lst.end(); ++i ) {
(*i)++;

}

But how do I use "for each, in" with STL containers (in unmanaged non CLR)
and still modify the elements of the containter?

you are mistaken about the meaninig of iterators.more over in C++ 'for
each' syntax does not exist;instead you can use the library function
'for_each'. Do something like this:

#include <algorithm>
#include <vector>

typedef std::vector<int> my_vector;

void my_code(my_vector::iterator it){
   //treat it as an 'int *'
   (*it)++;
};

int main(void){
    my_vector lst;
    lst.push_back(1);
    lst.push_back(2);
    lst.push_back(3);

    for_each(lst.begin(),lst.end(),my_code);

    return 0;
};