On Tue, Sep 16, 2008 at 3:00 PM, Peter Barker <newbarker@gmail.com> wrote:

On Mon, Sep 15, 2008 at 9:20 PM, Robert Dailey <rcdailey@gmail.com> wrote:

...

Hi,

Is there a way I can use std::for_each() on a boost::ptr_map and have the functor object be given the *value* of each item iterated instead of a key/value pair like it does with std::map? Help is appreciated, thank you.

std::for_each() with std::map receives the pair so you need something like the following to extract the value:

#include <algorithm> #include <iostream> #include <map> #include <string>

#include <boost/bind.hpp>

class MyClass { public: MyClass(int x) : x_(x) {} int getX() const {return x_;} private: int x_; };

void func(MyClass* mc) { std::cout << mc->getX() << std::endl; }

int main() { typedef std::map<std::string,MyClass*> MapType; MapType myPtrMap;

std::string key1 = "Key1"; std::string key2 = "Key2"; myPtrMap.insert(std::make_pair(key1,new MyClass(1))); myPtrMap.insert(std::make_pair(key2,new MyClass(2))); std::for_each(myPtrMap.begin(),myPtrMap.end(),boost::bind(&func,boost::bind(&MapType::value_type::second,_1))); }

Here's the same code working with ptr_map:

#include <algorithm> #include <iostream> #include <string>

#include <boost/bind.hpp> #include <boost/ptr_container/ptr_map.hpp>

class MyClass { public: MyClass(int x) : x_(x) {} int getX() const {return x_;} private: int x_; };

void func(MyClass* mc) { std::cout << mc->getX() << std::endl; }

int main() { typedef boost::ptr_map<std::string,MyClass> MapType; MapType myPtrMap;

std::string key1 = "Key1"; std::string key2 = "Key2"; myPtrMap.insert(key1,new MyClass(1)); myPtrMap.insert(key2,new MyClass(2)); std::for_each(myPtrMap.begin(),myPtrMap.end(),boost::bind(&func,boost::bind(&MapType::value_type::second,_1))); }

I hope that helps you out.

Regards,

Pete _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

At risk of sounding a complete wally, I have completely failed to understand why the second version is any way preferrable to the first. Why would you want to do this? - Rob.

On Tue, Sep 16, 2008 at 3:25 PM, Peter Barker <newbarker@gmail.com> wrote:

...

At risk of sounding a complete wally, I have completely failed to understand why the second version is any way preferrable to the first.

Why would you want to do this?

- Rob.

Are you asking why you would you use a boost::ptr_map over a std::map? I believe it's so the container takes ownership of the pointed to objects. http://www.boost.org/doc/libs/1_35_0/libs/ptr_container/doc/ptr_container.ht... contains this line:

"For each of the standard containers there is a pointer container equivalent that takes ownership of the objects in an exception safe manner. In this respect the library is intended to solve the so-called polymorphic class problem."

Regards,

Pete _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

Ah I see,.... so the code for ptr_map is intended to be as much like the code for std::map as possible! Got it now, thanks. - Rob. -- ACCU - Professionalism in programming - http://www.accu.org