使用new[]后使用delete[]根本原因

需要分情况讨论：以下环境为Ubuntu20.04 g++ 9.4.0

• 当数据是基本数据类型时,由于没有析构函数，所以系统没有必要记录数组大小。所以new[]后的指针就是实际申请内存大小，所以delete与delete[]没有区别,以下代码是不会抛出申请与释放指针不一致异常

  
  #include <iostream>
  int main() {
      int * a = new int[10] ;
      delete a;
      getchar();
      return 0;
  }
  
  

• 当数据为自定义数据类型时，由于需要挨个调用析构函数，所以在mallco时会多申请一个8位，来存储数组大小，导致new返回的指针并不是原始指针,而是在mallco的指针移动8位后的指针。

  1. 当delete,到operator delete执行时就是new返回的指针，而不是真实指针。所以释放会抛出申请与释放指针不一致异常

     #include <iostream>
     using namespace std;
     class A
     {
     public:
         A()
         {
         }
         ~A()
         {
             std::cout << "A" << std::endl;
         }
     
         static void operator delete[](void* ptr)
         {
             std::cout << "custom delete for PTR " << ptr << '\n';
             ::operator delete[](ptr);
         }
         static void operator delete(void* ptr, std:: size_t sz )
         {
             std::cout << "custom delete for PTR " << ptr << '\n';
             ::operator delete(ptr);
         }
     };
     
     int main() {
     
         A * a = new A[10] ;
         std::cout << a << std::endl;
         delete a;
         getchar();
         return 0;
     }
     

     0x558f7965aeb8
     A
     custom delete for PTR 0x558f7965aeb8
     munmap_chunk(): invalid pointer
     Aborted (core dumped)

  2. 当**delete[]**时，调用operator delete[]时执行的指针就是new返回的指针移动8位后的指针，正好是mallco出来的指针，这样就不会异常

     #include <iostream>
     using namespace std;
     class A
     {
     public:
         A()
         {
         }
         ~A()
         {
             std::cout << "A" << std::endl;
         }
     
         static void operator delete[](void* ptr)
         {
             std::cout << "custom delete for PTR " << ptr << '\n';
             ::operator delete[](ptr);
         }
         static void operator delete(void* ptr, std:: size_t sz )
         {
             std::cout << "custom delete for PTR " << ptr << '\n';
             ::operator delete(ptr);
         }
     };
     
     int main() {
     
         A * a = new A[10] ;
         std::cout << a << std::endl;
         delete[] a;
         getchar();
         return 0;
     }
     

     0x560989727eb8
     A
     A
     A
     A
     A
     A
     A
     A
     A
     A
     custom delete for PTR 0x560989727eb0