How can I detect the last iteration in a loop over std::map?

Question

I\'m trying to figure out the best way to determine whether I\'m in the last iteration of a loop over a map in order to do something like the following:

for          


        

Answer 1

Why to work to find the EOF so that you dont give something to it.

Simply, exclude it;

for (iter = someMap.begin(); someMap.end() - 1; ++iter) {
    //apply to all from begin to second last element
}

KISS (KEEP IT SIMPLY SIMPLE)

Answer 2

#include <boost/lambda/lambda.hpp>
#include <boost/lambda/bind.hpp>
#include <algorithm>

using namespace boost::lambda;

// call the function foo on each element but the last...
if( !someMap.empty() )
{
  std::for_each( someMap.begin(), --someMap.end(), bind( &Foo, _1 ) );
}

Using std::for_each will ensure that the loop is tight and accurate... Note the introduction of the function foo() which takes a single argument (the type should match what is contained in someMap). This approach has the added addition of being 1 line. Of course, if Foo is really small, you can use a lambda function and get rid of the call to &Foo.

Answer 3

How about this, no one mentioning but...

for (iter = someMap.begin(); iter != someMap.end(); ++iter) {
    // do something for all iterations
    if (iter != --someMap.end()) {
        // do something for all but the last iteration
    }
}

this seems simple, mm...

Answer 4

Full program:

#include <iostream>
#include <list>

void process(int ii)
{
   std::cout << " " << ii;
}

int main(void)
{
   std::list<int> ll;

   ll.push_back(1);
   ll.push_back(2);
   ll.push_back(3);
   ll.push_back(4);
   ll.push_back(5);
   ll.push_back(6);

   std::list<int>::iterator iter = ll.begin();
   if (iter != ll.end())
   {
      std::list<int>::iterator lastIter = iter;
      ++ iter;
      while (iter != ll.end())
      {
         process(*lastIter);
         lastIter = iter;
         ++ iter;
      }
      // todo: think if you need to process *lastIter
      std::cout << " | last:";
      process(*lastIter);
   }

   std::cout << std::endl;

   return 0;
}

This program yields:

 1 2 3 4 5 | last: 6

Answer 5

If you just want to use a ForwardIterator, this should work:

for ( i = c.begin(); i != c.end(); ) {
        iterator cur = i++;
        // do something, using cur
        if ( i != c.end() ) {
                // do something using cur for all but the last iteration
        }
}

Answer 6

For someone who likes C++11 range-based loop:

    for (const auto& pair : someMap) {
      if (&pair != &*someMap.rbegin()) ...
    }

Notice only reference type works here, not auto pair