Thinking more...

/**
 *       Filename:  test_new.cpp
 *    Description:  Test new(storage) Person();
 */
#include <cstdlib>
#include <string>
#include <iostream>

class Person {
	public:
		Person() {}
		~Person() {}

		std::string getName() { return _name; };
		void setName( std::string name ) { _name=name; }

		std::string toString() { return _name; }
	private:
		std::string _name;
};

int main( int argc, char* argv[] ) {
	char* storage = (char*)malloc( 1024 ); // allocate 1K

	Person* person = new(storage) Person();
	person->setName( "anonymous" );
	std::cout << person->toString() << std::endl;

	// if just storage, person will be replaced by intArray. (2)
	// int* intArray = new(storage) int[10];
	int* intArray = new(storage+sizeof(person)) int[10];
	int i=0;

	// assign value.
	for( i=0; i<10; i++ )
		intArray[i] = i;

	// show the values
	for( i=0; i<10; i++ )
		printf( "%d ", intArray[i]);
	printf("\n");

	// dump storage
	char* iter=storage;
	printf("=== begin dump ===\n");
	i=0;
	while( i!=512 ) {
		printf( "%02x ", (unsigned char)*iter );
		iter++;
		i++;
		if( !(i%16) )
			printf( "\n" );
	}
	printf("=== end dump ===\n");

	printf( "person address = %08x intArray address = %08x\n",
			(unsigned int)person, (unsigned int)intArray );

	// cannot delete, it cause segmentation fault. (1)
	//delete person;
	//delete[] intArray;

	// but we can use free.
	free( storage );
}

1. new(storage) Person() 實際上是 new 在 storage 這塊空間裡面，所以之後如果呼叫 delete，會出錯。
2. 如果不累加 storage 的話，會把之前配置的空間覆蓋掉。
3. malloc() 可以用 shmget()、shmat() 代替，沒有問題。
4. 以上面的例子，std::string 會配置一塊空間來放字串，這塊空間並不在 storage 裡面，使用時要注意。如果要這樣用，應該要再取代掉 STL allocator 的機制。