Re: [Boost-users] Using Boost::Bind

Subject: Re: [Boost-users] Using Boost::Bind
From: Michael Caisse (boost_at_[hidden])
Date: 2011-06-29 12:57:22

On 06/29/2011 09:32 AM, David McCallum wrote:
> Oops, that should have been:
>
> void DClient::resolveHandler(int param)
> {
>     ....
> }
>
> boost::function<void (int)>  functionPtr;
> int tempInt = 12;
>
> functionPtr = boost::bind(&DClient::resolveHandler, this, tempInt);
> functionPtr(67);
>
> The final line will call resolveHandler with a parameter of 12, rather
> than 67? Surely that can't be right?
> _______________________________________________
>    

It is absolutely correct. You have bound a value to the first argument.

If you want to bind a 'placeholder' based on when the bound functor is 
called then you use a placeholder:

functionPtr = boost::bind(&DClient::resolveHandler, this, _1);
functionPtr(67);

This would call DClient::resolveHandler with 67.

In the Asio slides I previously linked to I have about 3-4 example 
slides that provide various bind constructs to help show how bind works.

When you bind a method you are providing all the arguments that will be 
used at call time. Some of those arguments might be values or references 
and others might actually be placeholders to be determined at call time.

For example:

functionPtr = boost::bind(&DClient::resolveHandler, this, _2);
functionPtr(67,42,"hi mom");

would result in resolveHandler getting called with 42 because the 
placeholder _2 says to use the second parameter at the call location.

Bind is a powerful concept. Take some time to look at the bind docs.

hth -
michael

-- 
Michael Caisse
Object Modeling Designs
www.objectmodelingdesigns.com