【C++内存管理】3_placement new

• placement new 允许我们将 object 构建于 allocated memory 中;
• 没有所谓 placement delete， 因为 placement new 根本没分配 memory;

• 亦或称呼与 placement new 对应的 operator delete 为 placement delete。

  #include <new>
  
  char *buf = new char[sizeof(Complex) * 3];
  Complex *pc = new(buf) Complex (1, 2);
  
  // ...
  
  delete[] buf;

  

Complex *pc = new(buf) Complex (1, 2);

编译器转换为 ==>

Complex *pc;
try {
    void* mem = operator new (sizeof(Complex), buf); // allocate
    pc = static_cast<Complex*>(mem);                 // cast
    pc->Complex::Complex(1, 2);                      // construct
}
catch(std::bad_alloc) {
    // 若 allocation 失败就不执行 constructor 
}

void* mem = operator new (sizeof(Complex), buf);

源码实现 ==>

void *operator new (size_t, viud *loc)
{
    return loc;
}