auto_handle 類別

發行項
08/03/2024

自動資源管理，可用來將虛擬句柄內嵌至 Managed 類型。

語法

template<typename _element_type>
ref class auto_handle;

參數

_element_type
要內嵌的Managed型別。

成員

公用建構函式

名稱	描述
auto_handle::auto_handle	建構函式 `auto_handle` 。
auto_handle::~auto_handle	解 `auto_handle` 構函式。

公用方法

名稱	描述
auto_handle::get	取得自主物件。
auto_handle::release	從 `auto_handle` 管理釋放物件。
auto_handle::reset	終結目前擁有的物件，並選擇性地擁有新的物件。
auto_handle::swap	以另一個 `auto_handle`交換物件。

公用運算子

名稱	描述
`auto_handle::operator->`	成員存取運算子。
auto_handle::operator=	指派運算子。
auto_handle::operator auto_handle	與相容型別之間的 `auto_handle` 類型轉換運算元。
auto_handle::operator bool	`auto_handle`在條件表達式中使用的運算符。
auto_handle::operator!	`auto_handle`在條件表達式中使用的運算符。

需求

頭檔<msclr\auto_handle.h>

命名空間 msclr

auto_handle::auto_handle

建構函式 auto_handle 。

auto_handle();
auto_handle(
   _element_type ^ _ptr
);
auto_handle(
   auto_handle<_element_type> % _right
);
template<typename _other_type>
auto_handle(
   auto_handle<_other_type> % _right
);

參數

_ptr
要擁有的物件。

_右
現有的 auto_handle。

範例

// msl_auto_handle_auto_handle.cpp
// compile with: /clr
#include "msclr\auto_handle.h"

using namespace System;
using namespace msclr;
ref class RefClassA {
protected:
   String^ m_s;
public:
   RefClassA(String^ s) : m_s(s) {
      Console::WriteLine( "in RefClassA constructor: " + m_s );
   }
   ~RefClassA() {
      Console::WriteLine( "in RefClassA destructor: " + m_s );
   }

   virtual void PrintHello() {
      Console::WriteLine( "Hello from {0} A!", m_s );
   }
};

ref class RefClassB : RefClassA {
public:
   RefClassB( String^ s ) : RefClassA( s ) {}
   virtual void PrintHello() new {
      Console::WriteLine( "Hello from {0} B!", m_s );
   }
};

int main()
{
   {
      auto_handle<RefClassA> a(gcnew RefClassA( "first" ) );
      a->PrintHello();
   }

   {
      auto_handle<RefClassB> b(gcnew RefClassB( "second" ) );
      b->PrintHello();
      auto_handle<RefClassA> a(b); //construct from derived type
      a->PrintHello();
      auto_handle<RefClassA> a2(a); //construct from same type
      a2->PrintHello();
   }

   Console::WriteLine("done");
}

in RefClassA constructor: first
Hello from first A!
in RefClassA destructor: first
in RefClassA constructor: second
Hello from second B!
Hello from second A!
Hello from second A!
in RefClassA destructor: second
done

auto_handle::~auto_handle

解 auto_handle 構函式。

~auto_handle();

備註

解構函式也會解構擁有的物件。

範例

// msl_auto_handle_dtor.cpp
// compile with: /clr
#include "msclr\auto_handle.h"

using namespace System;
using namespace msclr;

ref class ClassA {
public:
   ClassA() { Console::WriteLine( "ClassA constructor" ); }
   ~ClassA() { Console::WriteLine( "ClassA destructor" ); }
};

int main()
{
   // create a new scope for a:
   {
      auto_handle<ClassA> a = gcnew ClassA;
   }
   // a goes out of scope here, invoking its destructor
   // which in turns destructs the ClassA object.

   Console::WriteLine( "done" );
}

ClassA constructor
ClassA destructor
done

auto_handle::get

取得自主物件。

_element_type ^ get();

傳回值

自主物件。

範例

// msl_auto_handle_get.cpp
// compile with: /clr
#include "msclr\auto_handle.h"

using namespace System;
using namespace msclr;

ref class ClassA {
   String^ m_s;
public:
   ClassA( String^ s ) : m_s( s ){
      Console::WriteLine( "in ClassA constructor:" + m_s );
   }
   ~ClassA() {
      Console::WriteLine( "in ClassA destructor:" + m_s );
   }

   void PrintHello() {
      Console::WriteLine( "Hello from {0} A!", m_s );
   }
};

void PrintA( ClassA^ a ) {
   a->PrintHello();
}

int main() {
   auto_handle<ClassA> a = gcnew ClassA( "first" );
   a->PrintHello();

   ClassA^ a2 = a.get();
   a2->PrintHello();

   PrintA( a.get() );
}

in ClassA constructor:first
Hello from first A!
Hello from first A!
Hello from first A!
in ClassA destructor:first

auto_handle::release

從 auto_handle 管理釋放物件。

_element_type ^ release();

傳回值

已發行的物件。

範例

// msl_auto_handle_release.cpp
// compile with: /clr
#include <msclr\auto_handle.h>

using namespace System;
using namespace msclr;

ref class ClassA {
   String^ m_s;
public:
   ClassA( String^ s ) : m_s( s ) {
      Console::WriteLine( "ClassA constructor: " + m_s );
   }
   ~ClassA() {
      Console::WriteLine( "ClassA destructor: " + m_s );
   }

   void PrintHello() {
      Console::WriteLine( "Hello from {0} A!", m_s );
   }
};

int main()
{
   ClassA^ a;

   // create a new scope:
   {
      auto_handle<ClassA> agc1 = gcnew ClassA( "first" );
      auto_handle<ClassA> agc2 = gcnew ClassA( "second" );
      a = agc1.release();
   }
   // agc1 and agc2 go out of scope here

   a->PrintHello();

   Console::WriteLine( "done" );
}

ClassA constructor: first
ClassA constructor: second
ClassA destructor: second
Hello from first A!
done

auto_handle::reset

終結目前擁有的物件，並選擇性地擁有新的物件。

void reset(
   _element_type ^ _new_ptr
);
void reset();

參數

_new_ptr
（選擇性）新的物件。

範例

// msl_auto_handle_reset.cpp
// compile with: /clr
#include <msclr\auto_handle.h>

using namespace System;
using namespace msclr;

ref class ClassA {
   String^ m_s;
public:
   ClassA( String^ s ) : m_s( s ) {
      Console::WriteLine( "ClassA constructor: " + m_s );
   }
   ~ClassA() {
      Console::WriteLine( "ClassA destructor: " + m_s );
   }

   void PrintHello() {
      Console::WriteLine( "Hello from {0} A!", m_s );
   }
};

int main()
{
   auto_handle<ClassA> agc1 = gcnew ClassA( "first" );
   agc1->PrintHello();

   ClassA^ ha = gcnew ClassA( "second" );
   agc1.reset( ha ); // release first object, reference second
   agc1->PrintHello();

   agc1.reset(); // release second object, set to nullptr

   Console::WriteLine( "done" );
}

ClassA constructor: first
Hello from first A!
ClassA constructor: second
ClassA destructor: first
Hello from second A!
ClassA destructor: second
done

auto_handle::swap

以另一個 auto_handle交換物件。

void swap(
   auto_handle<_element_type> % _right
);

參數

_右
auto_handle要交換物件的。

範例

// msl_auto_handle_swap.cpp
// compile with: /clr
#include <msclr\auto_handle.h>

using namespace System;
using namespace msclr;

int main() {
   auto_handle<String> s1 = "string one";
   auto_handle<String> s2 = "string two";

   Console::WriteLine( "s1 = '{0}', s2 = '{1}'",
      s1->ToString(), s2->ToString() );
   s1.swap( s2 );
   Console::WriteLine( "s1 = '{0}', s2 = '{1}'",
      s1->ToString(), s2->ToString() );
}

s1 = 'string one', s2 = 'string two'
s1 = 'string two', s2 = 'string one'

`auto_handle::operator->`

成員存取運算子。

_element_type ^ operator->();

傳回值

由 auto_handle包裝的物件。

範例

// msl_auto_handle_op_arrow.cpp
// compile with: /clr
#include <msclr\auto_handle.h>

using namespace System;
using namespace msclr;

ref class ClassA {
protected:
   String^ m_s;
public:
   ClassA( String^ s ) : m_s( s ) {}

   virtual void PrintHello() {
      Console::WriteLine( "Hello from {0} A!", m_s );
   }

   int m_i;
};

int main() {
   auto_handle<ClassA> a( gcnew ClassA( "first" ) );
   a->PrintHello();

   a->m_i = 5;
   Console::WriteLine( "a->m_i = {0}", a->m_i );
}

Hello from first A!
a->m_i = 5

auto_handle::operator=

指派運算子。

auto_handle<_element_type> % operator=(
   auto_handle<_element_type> % _right
);
template<typename _other_type>
auto_handle<_element_type> % operator=(
   auto_handle<_other_type> % _right
);

參數

_右
auto_handle要指定給目前auto_handle的。

傳回值

目前的 auto_handle，現在擁有 _right。

範例

// msl_auto_handle_op_assign.cpp
// compile with: /clr
#include <msclr\auto_handle.h>

using namespace System;
using namespace msclr;

ref class ClassA {
protected:
   String^ m_s;
public:
   ClassA(String^ s) : m_s(s) {
      Console::WriteLine( "in ClassA constructor: " + m_s );
   }
   ~ClassA() {
      Console::WriteLine( "in ClassA destructor: " + m_s );
   }

   virtual void PrintHello() {
      Console::WriteLine( "Hello from {0} A!", m_s );
   }
};

ref class ClassB : ClassA {
public:
   ClassB( String^ s ) : ClassA( s ) {}
   virtual void PrintHello() new {
      Console::WriteLine( "Hello from {0} B!", m_s );
   }
};

int main()
{
   auto_handle<ClassA> a;
   auto_handle<ClassA> a2(gcnew ClassA( "first" ) );
   a = a2; // assign from same type
   a->PrintHello();

   auto_handle<ClassB> b(gcnew ClassB( "second" ) );
   b->PrintHello();
   a = b; // assign from derived type
   a->PrintHello();

   Console::WriteLine("done");
}

in ClassA constructor: first
Hello from first A!
in ClassA constructor: second
Hello from second B!
in ClassA destructor: first
Hello from second A!
done
in ClassA destructor: second

auto_handle::operator auto_handle

與相容型別之間的 auto_handle 類型轉換運算元。

template<typename _other_type>
operator auto_handle<_other_type>();

傳回值

目前 auto_handle 轉換成 auto_handle<_other_type>。

範例

// msl_auto_handle_op_auto_handle.cpp
// compile with: /clr
#include <msclr\auto_handle.h>

using namespace System;
using namespace msclr;

ref class ClassA {
protected:
   String^ m_s;
public:
   ClassA( String^ s ) : m_s( s ) {}

   virtual void PrintHello() {
      Console::WriteLine( "Hello from {0} A!", m_s );
   }
};

ref class ClassB : ClassA {
public:
   ClassB( String ^ s) : ClassA( s ) {}
   virtual void PrintHello() new {
      Console::WriteLine( "Hello from {0} B!", m_s );
   }
};

int main() {
   auto_handle<ClassB> b = gcnew ClassB("first");
   b->PrintHello();
   auto_handle<ClassA> a = (auto_handle<ClassA>)b;
   a->PrintHello();
}

Hello from first B!
Hello from first A!

auto_handle::operator bool

auto_handle在條件表達式中使用的運算符。

operator bool();

傳回值

true 如果包裝的物件有效，則為 ; false 否則。

備註

這個運算符實際上會轉換成 _detail_class::_safe_bool 比更安全 bool 的，因為它無法轉換成整數類型。

範例

// msl_auto_handle_operator_bool.cpp
// compile with: /clr
#include <msclr\auto_handle.h>

using namespace System;
using namespace msclr;

int main() {
   auto_handle<String> s1;
   auto_handle<String> s2 = "hi";
   if ( s1 ) Console::WriteLine( "s1 is valid" );
   if ( !s1 ) Console::WriteLine( "s1 is invalid" );
   if ( s2 ) Console::WriteLine( "s2 is valid" );
   if ( !s2 ) Console::WriteLine( "s2 is invalid" );
   s2.reset();
   if ( s2 ) Console::WriteLine( "s2 is now valid" );
   if ( !s2 ) Console::WriteLine( "s2 is now invalid" );
}

s1 is invalid
s2 is valid
s2 is now invalid

auto_handle::operator!