place stl container object on shared memory

Hi, C++ programmers

I am trying to place an STL container object on shared memory and I
got a Segmentation Fault. Please give me some advice. Please notice
that if I allocate memory locally then I can place pStr on the
address
I sepcify. My platform is SunOS 5.10.

dbtouch

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <string>

#define CHECK_RESULT(X, Y) \
  if (X==-1) \
  { \
    perror(Y); \
    exit(EXIT_FAILURE); \
  }

typedef std::vector<int> VecInt;
typedef std::string String;

int main() {
  // create shared memory
  int result=shmget(IPC_PRIVATE, 1024*1024, 0644 | IPC_CREAT);
  if (result==-1) {
    perror("shmget");
    exit(EXIT_FAILURE);
  }

  int shmid=result;

  // attach shared memory
  char *ptr=NULL;
  ptr=(char*)shmat(shmid, NULL, 0644);
  if ((int)ptr==-1) {
    perror("shmat");
    exit(EXIT_FAILURE);
  }

#if 0
  VecInt* pVec=new(ptr)VecInt(10);
  delete pVec;
#endif

  // char* qtr=new char[1024*1024];
  // String* pStr=new(ptr)String(); good
  String* pStr=new(ptr)String(); // segment fault!!!
  if (pStr) {
    delete pStr;
    printf("test is good\n");
  }
  result=shmdt(ptr);
  CHECK_RESULT(result, "shmdt")

  result=shmctl(shmid, IPC_RMID, NULL);
  CHECK_RESULT(result, "shctl")

  exit(EXIT_SUCCESS);

}