[boost] shared_ptr w/ STL algorithm for_each

From: John Hunter (jdhunter_at_[hidden])
Date: 1999-11-01 18:00:24

I have a piece of sample code in which I have a vector of shared
pointers (boost::shared_ptr<>).  Can anyone tell me why I am unable to
iterate using the STL algorithm for_each (fail to compile; message
below) but I can manually loop over the container just fine.

e.g.
  //this works
  vector<Aptr>::iterator ix;
  for (ix = x.begin(); ix != x.end(); ++ix) 
    (*ix)->print();
  
  //this doesn't
  std::for_each(x.begin(), x.end(), std::mem_fun(&Base::print));  

Thanks in advace; complete code and compiler error message below.

John Hunter

Code:
#include <iostream>
#include <string>
#include <map>
#include <memory>
#include <vector>
#include <algorithm>
#include <boost/smart_ptr.hpp>

class Base {
public:
  virtual ~Base() {};
  virtual void print() = 0;
  virtual Base* clone() const { } ;
};

class Foo : public Base {
  int x;
public:
  Foo() : x(0) {};
  ~Foo () { std::cout << "Foo: ouch" << endl; }
  void print() { std::cout << "I am Foo" << endl;}
  Foo* clone() const { return new Foo(*this); }
};

class Bar : public Base {
  int x;
public:
  Bar() : x(0) {};
  ~Bar () { std::cout << "Bar: ouch" << endl; }
  void print() { std::cout << "I am Bar" << endl;}
  Bar* clone() const { return new Bar(*this); }
};

int main() {

  const Foo foo;
  const Bar bar;

  typedef std::map<const std::string, const Base*> Map;
  Map m;
  m["foo"] = &foo;
  m["bar"] = &bar;

  typedef boost::shared_ptr<Base> Aptr; 
  vector<Aptr> x;

  std::string s;
  std::cout << "enter foo or bar" << endl;
  while (cin >> s)
    x.push_back(Aptr(m[s]->clone())); //use the constructor

  //this works
  vector<Aptr>::iterator ix;
  for (ix = x.begin(); ix != x.end(); ++ix) 
    (*ix)->print();
  
  //this doesn't
  std::for_each(x.begin(), x.end(), std::mem_fun(&Base::print));  
}

Compiler error message:
localhost:~/c/examples> g++ test.cpp
g++ test.cpp

/usr/local/lib/gcc-lib/i586-pc-linux-gnu/2.95/../../../../include/g++-3/stl_algo.h:
In function `class mem_fun_t<void,Base> for_each<main()::Aptr *,
mem_fun_t<void,Base> >(main()::Aptr *, main()::Aptr *,
mem_fun_t<void,Base>)':
test.cpp:58:   instantiated from here
/usr/local/lib/gcc-lib/i586-pc-linux-gnu/2.95/../../../../include/g++-3/stl_algo.h:83:
no match for call to `(mem_fun_t<void,Base>) (boost::shared_ptr<Base>
&)'
/usr/local/lib/gcc-lib/i586-pc-linux-gnu/2.95/../../../../include/g++-3/stl_function.h:566:
candidates are: void mem_fun_t<void,Base>::operator ()(Base *) const
localhost:~/c/examples>