Re: [Boost-users] How to use bind/lambda in a conditional

8 Sep 2006

      ...
From: "Andriy Tylychko
...
Baranowski, Daniel
std::for_each(myVector.begin(), myVector.end(),
boost::lambda::if_then(boost::lambda::_1 == 3, [...]));
Best regards,
Andriy Tylychko
Thanks Andriy! That definitely got me on the correct track! It still
took me awhile, but I got it! It looks so simple now. Anyhow, since I'm
sure I'm not the only person that will ever have this problem when
learning to use bind and lambda, here is a sample program that I wrote
in vc8 to figure out the solution:

#include <vector>
#include <iostream>
#include <conio.h>

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

using namespace std;
using namespace boost;

using boost::lambda::_1;
using boost::lambda::if_then;

struct MyObjectClass
{
   MyObjectClass(int Data)
   : MyData(Data)
   {
   };

   int GetData() const
   {
      return MyData;
   };

   int MyData;
};

class TestClass
{
      typedef vector<MyObjectClass> t_ObjVector;
      t_ObjVector myVector;

      void PrintObj(const MyObjectClass & MyObj)
      {
         cout << MyObj.GetData() << endl;
      }

      void PrintInt(int MyInt)
      {
         cout << MyInt << endl;
      }

   public:
      TestClass()
      {
         myVector.push_back( MyObjectClass(1) );
         myVector.push_back( MyObjectClass(2) );
         myVector.push_back( MyObjectClass(2) );
         myVector.push_back( MyObjectClass(3) );
         myVector.push_back( MyObjectClass(3) );
         myVector.push_back( MyObjectClass(4) );
      }

      void RunTest()
      {
         // regular for loop
         t_ObjVector::iterator end = myVector.end();
         t_ObjVector::iterator itr = myVector.begin();
         for(itr; itr != end; ++itr)
         {
            if((*itr).GetData() == 3)
               PrintObj(*itr);
         }

         // for_each using lambda concepts
         for_each(myVector.begin(), myVector.end(), 
            if_then(bind(&MyObjectClass::GetData, _1) == 3, 
               bind(&TestClass::PrintObj, this, _1)
            ) 
         );
      }
};

int main (int argc, char **argv)
{  
   TestClass Test;

   // Run the test
   Test.RunTest();

   getch();

   return 0;
}

Thanks again for the help!
Daniel
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