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问题 I'm learning C++ and writing a binary search tree. The following is the code I wrote for my insert method. BSTNode * BST::Insert(const std::string & v) { BSTNode *n = !root ? root = new BSTNode(v) : Insert_Helper(v,root); if(n) size++; return n; } BSTNode * BST::Insert_Helper(const std::string & v, BSTNode *n) { if(!n->value.compare(v)) return NULL; // already have v else if(n->value.compare(v) > 0) // v goes to the left if(n->left) return Insert_Helper(v,n->left); else return n->left = new

问题 I'm learning C++ and writing a binary search tree. The following is the code I wrote for my insert method. BSTNode * BST::Insert(const std::string & v) { BSTNode *n = !root ? root = new BSTNode(v) : Insert_Helper(v,root); if(n) size++; return n; } BSTNode * BST::Insert_Helper(const std::string & v, BSTNode *n) { if(!n->value.compare(v)) return NULL; // already have v else if(n->value.compare(v) > 0) // v goes to the left if(n->left) return Insert_Helper(v,n->left); else return n->left = new

问题 Say I have some Java code: public class Widget { ...whatever } And some code that classloads the Widget : ClassLoader widgetLoader = Widget.class.getClassLoader(); Can widgetLoader ever be null ? Why/why not? If so, under what circumstances? 回答1: According to this method javadoc: Returns the class loader for the class. Some implementations may use null to represent the bootstrap class loader. This method will return null in such implementations if this class was loaded by the bootstrap class

问题 I was wondering how to get radio button values. So suppose, I have a form that has two radio buttons. I would like to get the value associated with the button. However, I get null when I try to. Form portion <form method="post" action="insert.jsp" enctype=text/plain> <table> <INPUT TYPE="radio" name="command" value="0">Run<INPUT TYPE="radio" NAME="command" VALUE="1">Walk<BR> Insert.jsp portion String sCommand=(String)request.getParameter("command"); out.println(sCommand); So in turn, it

问题 We have an ASP.NET web service that invokes a stored procedure on our DB (Oracle 11g). The problem is that the call to the procedure blows up every time an empty string is passed as one of the parameters. We're seeing an ORA-01084 error, which indicates to me that call is failing before the procedure is actually run. Here's the procedure, minus some logic that I believe is not relevant: PROCEDURE CreateReport ( from_dt IN NVARCHAR2, to_dt IN NVARCHAR2, p_table_id IN NVARCHAR2, p_column_id IN

问题 In converting from Swift 2.3 to Swift 3, I receive the error above for the following line of code: var contactButton: UIBarButtonItem {return self.CustomRightItem("icon-nav-nls-contact", target: self, action: nil)} The problem is on the nil action. I've tried using and empty selector: #selector() and ```#selector(nil) both to no avail. How can I handle a nil action in Swift 3? 回答1: This is clearly placeholder code for a later action, so use a placeholder function where the code will

问题 Given this table: SELECT * FROM CommodityPricing order by dateField "SILVER";60.45;"2002-01-01" "GOLD";130.45;"2002-01-01" "COPPER";96.45;"2002-01-01" "SILVER";70.45;"2003-01-01" "GOLD";140.45;"2003-01-01" "COPPER";99.45;"2003-01-01" "GOLD";150.45;"2004-01-01" "MERCURY";60;"2004-01-01" "SILVER";80.45;"2004-01-01" As of 2004, COPPER was dropped and mercury introduced. How can I get the value of (array_agg(value order by date desc) ) [1] as NULL for COPPER ? select commodity,(array_agg(value

问题 Is there a way to hide rowGroups with NULL values in Crosstab ? 来源： https://stackoverflow.com/questions/14221656/hide-null-row-groups-jasperreports

问题 This question already has answers here : Closed 10 years ago . Dupe: Null Difference A lifetime ago I came across an article that explained that the following were not equal (in c#): if (o == null) {} if (null == o) {} The article explained that the latter was preferred because it resulted in a more accurate test. I've been coding like that ever since. Now that I understand so much more I was looking for the article, or another like it, to see what the exact findings were, but I can't find

问题 I have a mutable class which has a private List<T> field inside. In the Reset() method of my class, should I clear the list using its Clear() method or just assign its field a new list? Note that the list is not public and is only used by the class itself. So assigning a new list should make the old one unreachable. Since the Clear() method is an O(n) operation, I wonder what is the downside of just assigning a new list over it. 回答1: The only downside I can think of is if you need to use the