Re: removing elements from vector<int> using <algorithm>

From:
"Jim Langston" <tazmaster@rocketmail.com>
Newsgroups:
comp.lang.c++
Date:
Wed, 10 Oct 2007 00:53:00 -0700
Message-ID:
<py%Oi.180$hO4.85@newsfe06.lga>
"arnuld" <NoSpam@NoPain.com> wrote in message
news:pan.2007.10.10.07.34.53.732995@NoPain.com...

WANTED:

/* C++ Primer - 4/e
*
* Exercise: 9.26
* STATEMENT
* Using the following definition of ia, copy ia into a vector and
into a list. Use the single iterator form of erase to remove the
elements with odd values from your list * and the even values from your
vector.

 int ia[] = { 0, 1, 1, 2, 3, 5, 8, 13, 21, 55, 89 };
*
*/

WHAT I GET:

/home/arnuld/programming/c++ $ g++ -ansi -pedantic -Wall -Wextra
ex_09.26.cpp ex_09.26.cpp:

In function 'int main()': ex_09.26.cpp:43:
error: '_1' was not declared in this scope /home/arnuld/programming/c++ $

CODE:

#include <iostream>
#include <vector>
#include <list>
#include <algorithm>
#include <iterator>

int main()
{
 int ia[] = { 0, 1, 1, 2, 3, 5, 8, 13, 21, 55, 89 };
 const size_t ia_size = sizeof( ia ) / sizeof( *ia );

 /* I made this array behave like a container:
       "ia_begin" is the pointer to 1st element of ia
"ia_end" is the pointer to one past the last element of ia
 */
 int *ia_begin = ia;
 int *ia_end = ia + ia_size;

 std::vector<int> ivec;
 std::list<int> ilist;

 /* copy elements from array to vector & list */
 std::copy( ia_begin, ia_end, std::back_inserter( ivec ) );
 std::copy( ia_begin, ia_end, std::back_inserter( ilist ) );

 std::remove_if( ivec.begin(),
  ivec.end(),
  _1 % 2 == 0 );

 /* print out the values */
 std::copy( ivec.begin(), ivec.end(),
            std::ostream_iterator<int> (std::cout, "\n" ) );

 return 0;
}

I am just trying to use Lambda from Std. Lib. Why it is the problem ?


You might want to re-read your homework assignment again. "... Use the
single iterator form of erase to remove the elements..." I don't believe
std::remove_if qualifies as erase. I believe the instructor may be looking
for ivec.erase( iterator ); but this is just how I read it.

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