DOM编程指南（一）

字符串型别
    C++ DOM使用普通的的无结尾标志的（XMLCh *）UTF-16字符串作为字符串型别，这些(XMLCh*) utf-16 型别的字符串开销极低。
   //C++ DOM
   const XMLCh* nodeValue = aNode->getNodeValue();
所有的字符串数据都将会保存在内存中直到文档对象被销毁。但是像这些字符串数据在执行过程中必要时有可能会被循环利用(RECYCLED)，用户应该使用合适的返回字符串副本作为类型安全的引用.
例如当一个DOMNode被释放后，为其分配的内存资源将会被循环在利用。

   XMLCh xfoo[] = {chLatin_f, chLatin_o, chLatin_o, chNull};

   // pAttr has node value = "foo"
   // fNodeValue has "foo"
   pAttr->setNodeValue(xfoo);
   const XMLCh* fNodeValue = pAttr->getNodeValue();

   // fNodeValue has "foo"
   // make a copy of the string for future reference
   XMLCh* oldNodeValue = XMLString::replicate(fNodeValue);

   // release the node pAttr
   pAttr->release()

   // other operations

   // implementation may have recycled the memory of the pAttr already
   // so it's not safe to expect fNodeValue still have "foo"
   if (XMLString::compareString(xfoo, fNodeValue))
       printf("fNodeValue has some other content\n");

   // should use your own safe copy
   if (!XMLString::compareString(xfoo, oldNodeValue))
       printf("Use your own copy of the oldNodeValue if want to reference the string later\n");

   // delete your own replicated string when done
   XMLString::release(&oldNodeValue);

    如果调用DOMNode::setNodeValue() 去设置一个新节点值，执行时仅仅是简单的重写节点值所占用的内存区域，因此先前的指针现在就会自动的指向新的值。用户应该使用合适的先前所返回的字符串副本作为类型安全的引用.例如：
    XMLCh xfoo[] = {chLatin_f, chLatin_o, chLatin_o, chNull};
   XMLCh xfee[] = {chLatin_f, chLatin_e, chLatin_e, chNull};

   // pAttr has node value = "foo"
   pAttr->setNodeValue(xfoo);
   const XMLCh* fNodeValue = pAttr->getNodeValue();

   // fNodeValue has "foo"
   // make a copy of the string for future reference
   XMLCh* oldNodeValue = XMLString::replicate(fNodeValue);

   // now set pAttr with a new node value "fee"
   pAttr->setNodeValue(xfee);

   // should not rely on fNodeValue for the old node value, it may not compare
   if (XMLString::compareString(xfoo, fNodeValue))
       printf("Should not rely on fNodeValue for the old node value\n");

   // should use your own safe copy
   if (!XMLString::compareString(xfoo, oldNodeValue))
       printf("Use your own copy of the oldNodeValue if want to reference the string later\n");

   // delete your own replicated string when done
   XMLString::release(&oldNodeValue);

     这样做是当我们成百上千次调用DOMNode::setNodeValue()时防止内存消耗成等比级数的增长。这一设计容许用户主动的选择返回的字符串应该手动的让它留在内存中还是将这个字符串拷贝到应用程序自己的堆栈中。（这句原文是This design allows users to actively select which returned string should stay in memory by manually copying the string to application's own heap.有些疑问，疑译文是我自己的理解）。

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