CLR語(yǔ)法中，值類(lèi)型指針?lè)譃閮煞N類(lèi)型：V*（限于非 CLR 堆位置）和內(nèi)部指針 interior_ptr<V>（允許但不要求托管堆內(nèi)的地址）。
釘住指針
通常，在壓縮階段，垃圾回收器可選擇將駐留在 CLR 堆上的對(duì)象移動(dòng)到堆內(nèi)的不同位置。這種移動(dòng)對(duì)于跟蹤句柄、跟蹤引用和內(nèi)部指針而言不是問(wèn)題，它們都透明地更新這些實(shí)體。但是，如果用戶(hù)在運(yùn)行時(shí)環(huán)境外傳遞了 CLR 堆上對(duì)象的地址，這種移動(dòng)就會(huì)導(dǎo)致問(wèn)題。在這種情況下，對(duì)象的不穩(wěn)定運(yùn)動(dòng)可能導(dǎo)致運(yùn)行時(shí)失敗。要避免此類(lèi)對(duì)象的移動(dòng)，必須在本地將它們釘在自己的位置上以供外部使用。
在托管擴(kuò)展中，“釘住指針”是通過(guò)使用 __pin 關(guān)鍵字限定指針聲明來(lái)聲明的。下面是一個(gè)來(lái)自托管擴(kuò)展規(guī)范的經(jīng)過(guò)略微修改的示例：
復(fù)制代碼
__gc struct H { int j; };
int main()
{
H * h = new H;
int __pin * k = & h -> j;
// …
};
在新的語(yǔ)言設(shè)計(jì)中，釘住指針是使用類(lèi)似于內(nèi)部指針的語(yǔ)法來(lái)聲明的。
復(fù)制代碼
ref struct H
{
public:
int j;
};
int main()
{
H^ h = gcnew H;
pin_ptr<int> k = &h->j;
// …
}
interior_ptr
Declares a pointer to inside a reference type, but not to the object itself. An interior pointer can point to a reference handle, value type, boxed type handle, member of a managed type, or to an element of a managed array.
cli::interior_ptr<cv_qualifier type> var = &initializer;
Remarks
A native pointer is not able to track an item as its location changes on the managed heap, which results from the garbage collector moving instances of an object. In order for a pointer to correctly refer to the instance, the runtime needs to update the pointer to the newly positioned object.
An interior_ptr represents a superset of the functionality of a native pointer. Therefore, anything that can be assigned to a native pointer can also be assigned to an interior_ptr. An interior pointer is permitted to perform the same set of operations as native pointers, including comparison and pointer arithmetic.
An interior pointer can only be declared on the stack. An interior pointer cannot be declared as a member of a class.
Since interior pointers exist only on the stack, taking the address of an interior pointer yields an unmanaged pointer.
interior_ptr has an implicit conversion to bool, which allows for its use in conditional statements.
For information on how to declare an interior pointer that points into an object that cannot be moved on the garbage-collected heap, see pin_ptr.
interior_ptr is in the cli namespace. See cli Namespace for more information.
//Example
// interior_ptr.cpp
// compile with: /clr
using namespace System;
ref class MyClass {
public:
int data;
};
int main() {
MyClass ^ h_MyClass = gcnew MyClass;
h_MyClass->data = 1;
Console::WriteLine(h_MyClass->data);
interior_ptr<int> p = &(h_MyClass->data);
*p = 2;
Console::WriteLine(h_MyClass->data);
// alternatively
interior_ptr<MyClass ^> p2 = &h_MyClass;
(*p2)->data = 3;
Console::WriteLine((*p2)->data);
}