Re: why boost:shared_ptr so slower?

I've just done a performance test on the shared_ptr compared to the
native pointer case, the results show at lease 3 times slower when the
iteration number > 10000, this is the code snippet:

#include <vector>
#include <iostream>
#include <boost/shared_ptr.hpp>

using namespace std;
using namespace boost;

class Thing
{
public:
 Thing()
 {
 }

 void method (void)
 {
   int i = 5;
 }
};

typedef boost::shared_ptr<Thing> ThingPtr;

void processThing(Thing* thing)
{
 thing->method();
}

//loop1 and loop2 test shared_ptr in the vector container
void loop1(long long num)
{
 vector<ThingPtr> thingPtrs;

 for(int i=0; i< num; i++) {
   ThingPtr p1(new Thing);
   thingPtrs.push_back(p1);
 }
}

void loop2(long long num)
{
 vector<Thing> thingPtrs;
 for(int i=0; i< num; i++) {
   Thing thing;
   thingPtrs.push_back(thing);
 }
 thingPtrs.clear();
}

//loop3 and loop4 test shared_ptr in the vector container
void loop3(long long num)
{
 for(int i=0; i< num; i++) {
   ThingPtr p1(new Thing);
   processThing(p1.get());
 }
}

void loop4(long long num)
{
 for(int i=0; i< num; i++) {
   Thing* p1 = new Thing();
   processThing(p1);
   delete p1;
 }
}

The results are the following:
CPU: Intel Core2 Quad CPU Q8200
RAM: 4G
OS: Windows XP SP2
Compiler: Visual Studio 2005

loop1 vs loop2: 100000 times
loop1 elapsed 390 msec
loop2 elapsed 93 msec

loop5 vs loop6: 100000 times
loop5 elapsed 171 msec
loop6 elapsed 78 msec