CObList::GetHead

CObject*& GetHead( );
CObject* GetHead( ) const;

返回值:
如果通过指向常量CObList的指针访问列表,那么GetHead将返回一个CObject指针。这将允许函数用于设定赋值的右边,并因此检测修改后的列表。
如果直接访问列表或通过指向CObList的指针进行访问列表,那么GetHead将返回一个CObject指针的参考。它允许函数用于赋值的两边,并因此修改列表入口。

说明:
获取代表列表首元素的CObject指针。
在调用GetHead函数之前,必须确保列表非空。如果列表为空,Microsoft基础类库的调试版将发出错误警告。请使用IsEmpty以证实列表中包含元素。

示例:
下面的例子说明了GetHead在赋值左边的用法。
const CObList* cplist;
CObList* plist = new CObList;
CAge* page1 = new CAge( 21 );
CAge* page2 = new CAge( 30 );
CAge* page3 = new CAge( 40 );
plist->AddHead( page1 );
plist->AddHead( page2 ); // List now contains (30, 21).
// The following statement REPLACES the head element.
plist->GetHead() = page3; // List now contains (40, 21).
ASSERT( *(CAge*) plist->GetHead() == CAge( 40 ) );
cplist = plist; // cplist is a pointer to a const list.
// cplist->GetHead() = page3; // Error: can't assign a pointer to a const list
ASSERT( *(CAge*) plist->GetHead() == CAge( 40 ) ); // OK delete page1;
delete page2;
delete page3;
delete plist; // Cleans up memory.

请参阅:
CObList::GetTail, CObList::GetTailPosition, CObList::AddHead, CObList::RemoveHead