wzsafepointertest.html

有限元学习研究用源代码(老外的),供科研人员参考

<TITLE>WZ 1.0 - Safe Pointer</TITLE>

<H1>Safe Pointer</H1>

<PRE>
#include "<A HREF="wzsafepointer.hxx">wzsafepointer.hxx</A>"

class ObjectClass: public wzProxyTarget{
public:
	int i;
	operator int() {return i;}
	const ObjectClass& operator=(const int& i0) {i=i0; return *this;}
	const ObjectClass& operator=(const ObjectClass& i0) {i=i0.i; return *this;}
        ObjectClass(int i0):i(i0){;}
};

typedef wzProxy<ObjectClass> PointerClass;

void test()
{
</PRE>

 <P>

<PRE>
 PointerClass y,z,z1,z2;
 {PointerClass x = new ObjectClass(10);
  ObjectClass& r1 = *(new ObjectClass(99));
  ObjectClass  r2(138); 
  PointerClass z2;
  now(x->accessCount()==1);
  y = x;
  now(x->accessCount()==2);
  (*x)=3;
  now(*y==3);
  now(r1.accessCount()==0);
  now(r2.accessCount()==0);
  z1 = &r1; z2=&r2; z=&r1;
  now(r1.accessCount()==2);
  now(r2.accessCount()==1);
  now(*z1==99);
  now(*z2==138);
  r1 = r2;
  now(*z1==138);
  now(r1.accessCount()==2);
  now(r2.accessCount()==1);
  now(y->accessCount()==2);
 }
 now(y->accessCount()==1);
</PRE>


<gA NAME="errors"> <hr></A>
<H2><A HREF="errors.html">Errors</A></H2>

<H3><A NAME="SafePointerHangingError">SafePointerHangingError</A></H3>

 <P>Because it is allowed to get the address of a local variable of
the object class, there may be pointers to the local variable at the
moment of destruction.  The classical error is the following:

<PRE>
 try{PointerClass x; 
	{ObjectClass X(11);
	 x = &amp;X;	// that's ok yet;
	 now(*x==11);	// indeed, no problem;
	}		// but now, X will be destroyed as a local variable;
	should_fail();	// after this, *x is invalid;
	{ObjectClass Y(12);	// probably the same address as X;
 	 *x = 123;	// this would be the worst case of overwriting Y;
	}
 }catch(wzProxyHangingError){;}
</PRE>

<H3><A NAME="SafePointerLockError">SafePointerLockError</A></H3>

 <P>You can forbid pointer access.  In this case, an attempt to do it
throws an exception.

<PRE>
 try{PointerClass x; 
	{ObjectClass X(11);
	 X.lockPointerAccess();
	 {{{{{ // somewhere hidden behind a lot of calls, the following happens:
		x = &amp;X;
		should_fail();
	}}}}}}
 }catch(wzProxyLockError){;}
</PRE>

<A NAME="End"> <hr></A>

<PRE>
}
</PRE>