下面哪条命令可用来确保文件“myfile”存在（）

A:cp myfile /devull B:touch myfile C:create myfile D:mkfile myfile

下面程序的结果是 ______。
#include＜iostream.h＞
class A
public:
virtual void fun（　）=0;
;
class B:public A
public:
void fun （　） cout＜＜ "new file" ;
;
class C: public A
public:
void fun （　）cout＜＜"open file"＜＜ " "
;
class D: public A
public:
void fun （　） cout＜＜ "save file/n" ;
;
void main（　）
A a,*p;
B b;
C c;
D d;
p=&c;
p-＞fun （　）;
p=&b;
p-＞fun （　）;
p=&d;
p-＞fun（　）;

A:new file open file save file B:new file new file new file C:编译出错 D:open file new file save file

下面程序的运算结果是( )。
#include＜iostream＞
using namespace std;
class A

public:
virtual void fun（　）=0;
;
class B:public A

public:
void fun（　）
cout＜＜"new file"＜＜" ";
;
class C:public A

public：
void fun（　）
cout＜＜"open file"＜＜" ";
;
void main（　）

A a, * p;
B b;C c;
p=&c;
p-＞fun（　）;
p=&b;

A:new file open file B:new file new file C:编译出错 D:open file new file

下面创建一个新文件对象方法错误的是( )。

A:File myFile;
myFile=new File("mulu/file"); B:File myFile=new File(); C:myFile=new FileC/mulu","filel"); D:File myDir=new file("/mulu");
myFile=new File(Dir, "filer');

假定通用对话框的名称为CommonDialogl，命令按钮的名称为Command1，则单击命令按钮后，能使打开的对话框的标题为“New File”的事件过程是______。

A:Private Sub Command1_Click() CommonDialog DialoqTitle="New File" CommonDialog ShowPrinter End Sub B:Private Sub ComJRandl_Click() CommonDialog DialogTitle="New File" CommonDialog ShowFont End Sub C:Private Sub Command1_Click() CommonDialog DialogTitle="New File" CommonDialog ShowOpen End Sub D:Private Sub Command1_Click() CommonDialog DialogTitle="New File" CommonDialog ShowColor End Sub

Which UNIX command creates a symbolic link named myfile in the current directory to the file/etc/hosts

A:In -s/etc/hosts myfile B:In -s myfile/etc/hosts C:link -s/etc/hosts myfile D:link -s myfile/etc/hosts

下面程序的结果是 ______。 #include＜iostream.h＞ class A{ public: virtual void fun（　）=0{}; }; class B:public A{ public: void fun （　） {cout＜＜ "new file" ;} }; class C: public A{ public: void fun （　）{cout＜＜"open file"＜＜ " " } }; class D: public A{ public: void fun （　） {cout＜＜ "save file/n" ;} }; void main（　） { A a,*p; B b; C c; D d; p=&c; p-＞fun （　）; p=&b; p-＞fun （　）; p=&d; p-＞fun（　）; }

A:new file open file save file B:new file new file new file C:编译出错 D:open file new file save file

Which UNIX command creates a symbolic link named myfile in the current directory to the file /etc/hosts ( )

A:In —s/etc/hosts myfile B:In —s myfile/etc/hosts C:link —s/etc/hosts myfile D:link —s myfile/etc/hosts

下面创建一个新文件对象方法错误的是( )。

A:File myFile；　　myFile=new File("mulu/file")； B:File myFile=new file( )； C:myFile=new File("/mulu","filel")； D:File myDir=new file("/mulu")；　　myFile=new File(Dir"filel")；

下面程序的运算结果是( )。 #include＜iostream＞ using namespace std; class A { public: virtual void fun（　）=0; }; class B:public A } public: void fun（　） {cout＜＜"new file"＜＜" ";} }; class C:public A { public： void fun（　） { cout＜＜"open file"＜＜" ";} }; void main（　） { A a, * p; B b;C c; p=&c; p-＞fun（　）; p=&b; }

A:new file open file B:new file new file C:编译出错 D:open file new file