[C++] 关于delete和delete[]

首先贴一段MFC的源代码：

void __cdecl operator delete(void* p)
{
        free(p);
}

void __cdecl operator delete[](void* p)
{
    ::operator delete(p);
}

然后贴一点汇编：

char* p = new char[100];<br />00402CE1 push 64h<br />00402CE3 call operator new[] (4051C6h)<br />00402CE8 add esp,4<br />00402CEB mov dword ptr [ebp-7Ch],eax<br />00402CEE mov eax,dword ptr [ebp-7Ch]<br />00402CF1 mov dword ptr [p],eax<br /> delete p;<br />00402CF4 mov eax,dword ptr [p]<br />00402CF7 mov dword ptr [ebp-78h],eax<br />00402CFA mov ecx,dword ptr [ebp-78h]<br />00402CFD push ecx<br />00402CFE call operator delete (4051C1h)<br />00402D03 add esp,4<br /> delete [] p;<br />00402D06 mov eax,dword ptr [p]<br />00402D09 mov dword ptr [ebp-74h],eax<br />00402D0C mov ecx,dword ptr [ebp-74h]<br />00402D0F push ecx<br />00402D10 call operator delete[] (4051CBh)<br />00402D15 add esp,4<br />

分析：

其中的call operator delete (4051C1h) 就是去调用MFC的void __cdecl operator delete(void* p)

其中的call operator delete[] (4051CBh) 就是去调用MFC的void __cdecl operator delete[](void* p)

所以在这种情下，两者是完全等效的。

A* a = new A[100];<br />00402D18 push 194h<br />00402D1D call operator new[] (4051C6h)<br />00402D22 add esp,4<br />00402D25 mov dword ptr [ebp-6Ch],eax<br />00402D28 mov dword ptr [ebp-4],0<br />00402D2F cmp dword ptr [ebp-6Ch],0<br />00402D33 je CTestMFCDlg::OnBnClickedButton9+0A3h (402D63h)<br />00402D35 mov eax,dword ptr [ebp-6Ch]<br />00402D38 mov dword ptr [eax],64h<br />00402D3E push offset A::~A (402E00h)<br />00402D43 push offset A::A (402DE0h)<br />00402D48 push 64h<br />00402D4A push 4<br />00402D4C mov ecx,dword ptr [ebp-6Ch]<br />00402D4F add ecx,4<br />00402D52 push ecx<br />00402D53 call `eh vector constructor iterator' (443BA8h)<br />00402D58 mov edx,dword ptr [ebp-6Ch]<br />00402D5B add edx,4<br />00402D5E mov dword ptr [ebp-80h],edx<br />00402D61 jmp CTestMFCDlg::OnBnClickedButton9+0AAh (402D6Ah)<br />00402D63 mov dword ptr [ebp-80h],0<br />00402D6A mov eax,dword ptr [ebp-80h]<br />00402D6D mov dword ptr [ebp-70h],eax<br />00402D70 mov dword ptr [ebp-4],0FFFFFFFFh<br />00402D77 mov ecx,dword ptr [ebp-70h]<br />00402D7A mov dword ptr [a],ecx<br /> delete a;<br />00402D7D mov eax,dword ptr [a]<br />00402D80 mov dword ptr [ebp-64h],eax<br />00402D83 mov ecx,dword ptr [ebp-64h]<br />00402D86 mov dword ptr [ebp-68h],ecx<br />00402D89 cmp dword ptr [ebp-68h],0<br />00402D8D je CTestMFCDlg::OnBnClickedButton9+0DEh (402D9Eh)<br />00402D8F push 1<br />00402D91 mov ecx,dword ptr [ebp-68h]<br />00402D94 call A::`scalar deleting destructor' (402EA0h)<br />00402D99 mov dword ptr [ebp-80h],eax<br />00402D9C jmp CTestMFCDlg::OnBnClickedButton9+0E5h (402DA5h)<br />00402D9E mov dword ptr [ebp-80h],0<br /> delete [] a;<br />00402DA5 mov eax,dword ptr [a]<br />00402DA8 mov dword ptr [ebp-5Ch],eax<br />00402DAB mov ecx,dword ptr [ebp-5Ch]<br />00402DAE mov dword ptr [ebp-60h],ecx<br />00402DB1 cmp dword ptr [ebp-60h],0<br />00402DB5 je CTestMFCDlg::OnBnClickedButton9+106h (402DC6h)<br />00402DB7 push 3<br />00402DB9 mov ecx,dword ptr [ebp-60h]<br />00402DBC call A::`vector deleting destructor' (402E20h)<br />00402DC1 mov dword ptr [ebp-80h],eax<br />00402DC4 jmp CTestMFCDlg::OnBnClickedButton9+10Dh (402DCDh)<br />00402DC6 mov dword ptr [ebp-80h],0<br />

分析：

其中的call  A::`scalar deleting destructor' (402EA0h) 会call A::~A (402E00h) 然后call operator delete (4051C1h)

其中的call  A::`vector deleting destructor' (402E20h)会循环的为每个对象call  `eh vector destructor iterator' (443C7Dh) 循环结束之后call operator delete[] (4051CBh)

结论：

1，对于char这样的基础数据类型，delete和delete[]是等价的。

2，对于class A这样带析构函数的类型，delete和delete[]是不同的。

3，如果只有一个对象，那么对象数组在逻辑上可以蜕化成一个对象，但是那样会多一些步骤，性能会稍差一些。这大概是C++需要同时保留delete和delete[]的原因。