Re: [Boost-users] [function][lambda] Create a boost function to a bind functor

19 Oct 2006

      It is binding 2 to the second argument of the function (which is b) but _1 
to a which means 
the argument you call f with is passed as a to your function. Hence f(3) 
prints 3 2 and returns 5.
If you want 2 3 you need:
boost::function f = 
boost::lambda::bind(fx,2,boost::lambda::_1);

cheers
Arnaldur

"Chris Weed"  
Sent by: boost-users-bounces@lists.boost.org
19.10.2006 12:18
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Re: [Boost-users] [function][lambda] Create a boost function to a bind 
functor

Hi,
I can get the following code to compile and it prints
3 2
5
but I don't quite understand why it doesn't print
2 3
5
or how to get it to do so. I thought since it is binding 2 to _1, this
would bind it to the a argument.

#include 
#include 
#include 
#include <iostream>

float fx(float a, float b)
{
  std::cout << a << " " << b << std::endl;
  return a+b;
}

int main()
{
  boost::function f = 
boost::lambda::bind(fx,boost::lambda::_1,2);
  std::cout << f(3) << std::endl;
  return 0;
}

Thanks,
Chris

On 10/19/06, Arnaldur Gylfason  wrote:
...
a) You want to use _1 instead of _2
b) _1/_2 are in namespace boost::lambda
boost::function f =
boost::lambda::bind(fx,boost::lambda::_1,2);
...
It is actually possible to use _2 but then the functor takes to args and
ignores the first:
...
boost::function f = 
boost::lambda::bind(fx,boost::lambda::_2,2);
   std::cout << f(100,3) << std::endl; // returns 5
cheers
Arnaldur
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