如何在指定地址上创建 C++ 对象？

// 52-2.cpp
#include <iostream>
#include <string>
using namespace std;
class Test
    static unsigned int c_count;
    static char* c_buffer;
    static char* c_map;
    int m_value;
public:
    static bool SetMemorySource(char* memory, unsigned int size)
        bool ret = false;
        c_count = size / sizeof(Test);
        ret = c_count && (c_map = reinterpret_cast<char*>(calloc(c_count, sizeof(char))));
        if (ret)
            c_buffer = memory;
            free(c_map);
            c_map = NULL;
            c_buffer = NULL;
            c_count = 0;
        return ret;
    void* operator new (unsigned int size)
        void* ret = NULL;
        if (c_count > 0)
            for (int i = 0; i < c_count; i++)
                if (!c_map[i])
                    c_map[i] = 1;
                    ret = c_buffer + i * sizeof(Test);
                    cout << "succeed to allocate memory: " << ret << endl;
                    break;
            ret = malloc(size);
        return ret;
    void operator delete(void* p)
        if (p != NULL)
            if (c_count > 0)
                char* mem = reinterpret_cast<char*>(p);
                int index = (mem - c_buffer) / sizeof(Test);
                int flag = (mem - c_buffer) % sizeof(Test);
                if (flag == 0 && 0 <= index && index < c_count)
                    c_map[index] = 0;
                    cout << "succeed to free memory: " << p << endl;
                free(p);
unsigned int Test::c_count = 0;
char* Test::c_buffer = NULL;
char* Test::c_map = NULL;
int main(int argc, char* argv[])
    char buffer[12] = { 0 };
    Test::SetMemorySource(buffer, sizeof(buffer));
    cout << "==== Test Single Object ====" << endl;
    Test* pt = new Test;
    delete pt;
    cout << "==== Test Object Array ====" << endl;
    Test* pa[5] = { 0 };
    for (int i = 0; i < 5; i++)
        pa[i] = new Test;
        cout << "pa[" << i << "]" << pa[i] << endl;
    for (int i = 0; i < 5; i++)
        cout << "delete " << pa[i] << endl;
        delete pa[i];
    return 0;
main 函数中的 buffer[12] 在栈中分配空间，将这个地址指定为 new 申请对象的地址，则 new 在栈中分配空间。
 
C++ 类中成员函数，static 变量不计算入 sizeof，buffer[12] 大小为 12 个字节，Test 大小为 4 字节，所以最多可以放置三个对象，我们申请了 5 个对象，所以只有前三个对象对申请成功。
 
==== Test Single Object ====
succeed to allocate memory: 00B5FE20
succeed to free memory: 00B5FE20
==== Test Object Array ====
succeed to allocate memory: 00B5FE20
pa[0]00B5FE20
succeed to allocate memory: 00B5FE24
pa[1]00B5FE24
succeed to allocate memory: 00B5FE28
pa[2]00B5FE28
pa[3]00000000
pa[4]00000000
delete 00B5FE20
succeed to free memory: 00B5FE20
delete 00B5FE24
succeed to free memory: 00B5FE24
delete 00B5FE28
succeed to free memory: 00B5FE28
delete 00000000
delete 00000000
1、new/delete 操作符可以重载，推荐针对具体类重载
 2、new 默认在堆上分配空间，重载可以在静态存储区、栈上分配空间