New 和 Delete
- 来源: https://www.freebasic.net/wiki/wikka.php?wakka=ProPgNewDelete
- 最后更新: 2022-11-29
不同的 New（隐式/重载/表达式/定位）和 Delete（隐式/重载/语句）运算符，以及它们的所有数组版本 New[] 和 Delete[]
定义
用户可能会对不同的 New 和 Delete 运算符感到困惑（尽管文档通过多个不同页面加以区分）：
'Operator New Implicit'（用户不可访问）：Operator New Overload：'Operator Delete Implicit'（用户不可访问）：Operator Delete Overload：Operator New Expression：Operator Delete Statement：Operator Placement New：
'Operator New[] Implicit/Overload/Expression'、'Operator Delete[] Implicit/Overload/Statement' 和 'Operator Placement New[]' 的定义类似，它们只是前述运算符的（一维）数组版本（会对数组元素进行构造/析构循环）。
使用 'Operator New Overload/Expression' 创建的实例必须使用 'Operator Delete Overload/Statement' 释放。
使用 'Operator New[] Overload/Expression' 创建的实例数组必须使用 'Operator Delete[] Overload/Statement'（即 'Operator Delete Overload/Statement' 的数组版本）释放。
用户不能混用不同版本的运算符。
使用 'Operator Placement New' 在指定内存地址构造的实例，绝不能在该地址上对应地使用任何 'Operator Delete' 进行释放（因为内存不是由 'Operator Placement New' 分配的）。
使用 'Operator Placement New[]' 在指定内存地址构造的实例数组，绝不能在该地址上对应地使用任何 'Operator Delete[]' 进行释放（因为内存不是由 'Operator Placement New[]' 分配的）。
对于此类 UDT 实例，如有必要仅销毁每个实例，正确的方式是仅调用析构函数（如果存在，无论是隐式还是显式），语法与使用成员访问运算符调用成员方法相同。
注意：任何 New[] 或 Delete[] 运算符（语句/表达式/重载运算符的数组版本），甚至重载运算符 Delete，都与继承多态性（子类型多态性）不直接兼容，因为使用子类型指针（而非真实类型）主要无法访问其他元素（第一个元素除外）。
算法（应用于用户定义类型）
Operator New/New[] Expression（New/New[] 表达式运算符）：
vb
' NEW/NEW[] 表达式运算符
' V
' |
' 若存在则调用 >----------------------------------.
' 否则 :
' v v
' （New/New[] 运算符隐式） （New/New[] 运算符重载）
' : :
' 基础内存分配 用户内存分配代码
' : :
' :<-------------------------------------'
' |
' |<-------------------------------------.
' | :
' 数据字段初始化 :
' 对象字段构造 :
' （VPTR 初始化） :
' | :
' 若存在则调用 >-------------. :
' 否则 : :
' v v :
' : （用户构造函数） :
' : : :
' : 用户代码 :
' : : :
' :<--------------------' :
' | :
' 若为数组版本 NEW[] 则循环 >------------------------'
' 否则
' v
' |
' VOperator Delete/Delete[] Statement（Delete/Delete[] 语句运算符）：
vb
' DELETE/DELETE[] 语句运算符
' V
' |
' |<-------------------------------------.
' | :
' （VPTR 重新初始化） :
' | :
' 若存在则调用 >-------------. :
' 否则 : :
' v v :
' : （用户析构函数） :
' : : :
' : 用户代码 :
' : : :
' :<--------------------' :
' | :
' 对象字段析构 :
' | :
' 若为数组版本 DELETE[] 则循环 >----------------------'
' 否则
' v
' |
' 若存在则调用 >----------------------------------.
' 否则 :
' v v
' (隐式 Delete/Delete[] 运算符) (重载 Delete/Delete[] 运算符)
' : :
' 基础内存释放 用户内存释放代码
' : :
' :<-------------------------------------'
' |
' VOperator Placement New/New[]（定位 New/New[] 运算符）：
vb
' 定位 NEW/NEW[] 运算符
' V
' |
' |<-------------------------------------.
' | :
' 数据字段初始化 :
' 对象字段构造 :
' （VPTR 初始化） :
' | :
' 若存在则调用 >-----------------. :
' 否则 : :
' v v :
' : (用户构造函数) :
' : : :
' : 用户代码 :
' : : :
' :<--------------------' :
' | :
' 若为数组版本 NEW[] 则循环 >------------------------'
' 否则
' v
' |
' V示例
使用 New（Overload/Expression/Placement）和 Delete（Overload/Statement）运算符及其所有数组版本 New[] 和 Delete[] 的示例：
（用户可访问的全部 10 个 New 和 Delete 运算符）：
start GeSHi
vb
Declare Sub printArray (ByRef label As String = "", array() As String)
Type UDT
Declare Constructor ()
Declare Destructor ()
Declare Operator New (ByVal size As UInteger) As Any Ptr ' Operator New Overload
Declare Operator New[] (ByVal size As UInteger) As Any Ptr ' Operator New[] Overload
Declare Operator Delete (ByVal buf As Any Ptr) ' Operator Delete Overload
Declare Operator Delete[] (ByVal buf As Any Ptr) ' Operator Delete[] Overload
Dim As String array (1 To 4)
End Type
Constructor UDT ()
Static As Integer n
Print " Constructor"
printArray(" init: @" & @This & " (descriptors) -> ", This.array())
For i As Integer = LBound(This.array) To UBound(This.array)
This.array(i) = Chr(Asc("a") + n + i - LBound(This.array))
Next i
printArray(" => ", This.array())
Print
n += UBound(This.array)- LBound(This.array) + 1
End Constructor
Destructor UDT ()
Print " Destructor"
printArray(" erase: @" & @This & " (descriptors) -> ", This.array())
Erase This.array
printArray(" => ", This.array())
Print
End Destructor
Operator UDT.New (ByVal size As UInteger) As Any Ptr
Print " Operator New Overload"
Dim As Any Ptr p = Allocate(size) ' Memory allocation (with passed size)
Print " memory allocation: ";
Print size & " Bytes from @" & p
Return p ' Returning memory pointer
End Operator
Operator UDT.New[] (ByVal size As UInteger) As Any Ptr
Print " Operator New[] Overload"
Dim As Any Ptr p = Allocate(size) ' Memory allocation (with passed size)
Print " memory allocation: ";
Print size & " Bytes from @" & p
Return p ' Returning memory pointer
End Operator
Operator UDT.Delete (ByVal buf As Any Ptr)
Print " Operator Delete Overload"
Deallocate(buf) ' Memory deallocation (with passed pointer)
Print " memory deallocation: ";
Print "for @" & buf
End Operator
Operator UDT.Delete[] (ByVal buf As Any Ptr)
Print " Operator Delete[] Overload"
Deallocate(buf) ' Memory deallocation (with passed pointer)
Print " memory deallocation: ";
Print "for @" & buf
End Operator
Print "Operator New Expression"
Dim As UDT Ptr pu1 = New UDT ' Operator New Expression
Print "Operator Delete Statement"
Delete pu1 ' Operator Delete Statement
Sleep
Print
Print "Operator New[] Expression"
Dim As UDT Ptr pu2 = New UDT[2] ' Operator New[] Expression
Print "Operator Delete[] Statement"
Delete[] pu2 ' Operator Delete[] Statement
Sleep
Dim As Byte buffer(1 To 256)
Dim As Any Ptr p = @buffer(1)
Print
Print "Operator Placement New"
Dim As UDT Ptr pu3 = New(p) UDT ' Operator Placement New
Print "User call of Destructor"
pu3->Destructor() ' User Call of Destructor
Sleep
Print
Print "Operator Placement New[]"
Dim As UDT Ptr pu4 = New(p) UDT[2] ' Operator Placement New[]
For i As Integer = 0 To 1
Print "User Call of Destructor"
pu4[i].Destructor() ' User Call of Destructor
Next i
Sleep
Sub printArray (ByRef label As String = "", array() As String)
Print label & "{";
For i As Integer = LBound(array) To UBound(array)
Print """" & array(i) & """";
If i < UBound(array) Then
Print ",";
End If
Next I
Print "}";
End Subend GeSHi
输出示例（64 位系统）：
vb
Operator New Expression
Operator New Overload
memory allocation: 96 Bytes from @1728352
Constructor
init: @1728352 (descriptors) -> {"","","",""} => {"a","b","c","d"}
Operator Delete Statement
Destructor
erase: @1728352 (descriptors) -> {"a","b","c","d"} => {"","","",""}
Operator Delete Overload
memory deallocation: for @1728352vb
Operator New[] Expression
Operator New[] Overload
memory allocation: 200 Bytes from @1728352
Constructor
init: @1728360 (descriptors) -> {"","","",""} => {"e","f","g","h"}
Constructor
init: @1728456 (descriptors) -> {"","","",""} => {"i","j","k","l"}
Operator Delete[] Statement
Destructor
erase: @1728456 (descriptors) -> {"i","j","k","l"} => {"","","",""}
Destructor
erase: @1728360 (descriptors) -> {"e","f","g","h"} => {"","","",""}
Operator Delete[] Overload
memory deallocation: for @1728352Operator Placement New
Constructor
init: @1375248 (descriptors) -> {"","","",""} => {"m","n","o","p"}
User call of Destructor
Destructor
erase: @1375248 (descriptors) -> {"m","n","o","p"} => {"","","",""}Operator Placement New[]
Constructor
init: @1375248 (descriptors) -> {"","","",""} => {"q","r","s","t"}
Constructor
init: @1375344 (descriptors) -> {"","","",""} => {"u","v","w","x"}
User Call of Destructor
Destructor
erase: @1375248 (descriptors) -> {"q","r","s","t"} => {"","","",""}
User Call of Destructor
Destructor
erase: @1375344 (descriptors) -> {"u","v","w","x"} => {"","","",""}参见
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