null | 易学教程

SuperObject cannot handle null string

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问题 Some JSON serializers return null for an empty string datafield, e.g. { "searchtext": null, "moretext": "contains something", "bookdate": 1377468000000, "empid": 12345, "listtype": 1 } I'm using SuperObject to create a ISuperObject: var FJSONRequest: ISuperObject; then FJSONRequest := SO(Request.Content); // Webservice request This returns an object with a string containing the text 'null' . Obviously this is because SuperObject does not care about the quotes ( "searchtext": a gives the same

Best way to check if column returns a null value (from database to .net application)

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问题 I have a table with a DateTime column the column can have NULL values Now I connect to the database using an ODBC connection and get the value into a DataTable in .net / c#. I am able to check it for NULL by going if(String.IsNullOrEmpty(table.rows[0][0].ToString()) { //Whatever I want to do } Is String.IsNullOrEmpty the correct way to check for null values. 回答1: Use DBNull.Value.Equals on the object without converting it to a string. Here's an example: if (! DBNull.Value.Equals(row[fieldName

What happens when a static method is invoked using a null object reference?

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问题 public class CallingStaticMethod { public static void method() { System.out.println("I am in method"); } public static void main(String[] args) { CallingStaticMethod csm = null; csm.method(); } } Can someone explain how the static method is invoked in the above code? 回答1: It's been optimized away by the compiler, simply because having an instance of the class is not necessary. The compiler basically replaces csm.method(); by CallingStaticMethod.method(); It's in general also a good practice

How do I handle null or optional dll struct parameters in C#

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问题 How do I deal with optional struct arguments in dll methods called from C# using pinvoke? For example, the lpSecurityAttributes parameter here should be passed null when absent. The correct way of passing struct 's seems to be using ref , but it cannot have optional parameters, or take null in general. What ways are there to achieve this? 回答1: You have a few options 1) Use a class instead of a struct I think this method is the easiest. Simply declare the struct as a class : [StructLayout

JS typeof 与 instanceof

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【推荐】2019 Java 开发者跳槽指南.pdf(吐血整理) >>> JS中常用来判定变量类型的两个函数为 typeof 和 instanceof typeof 的结果有 undefined, number, boolean, string, function, object[ null, Array, String, Date.....] 要注意的地方是 typeof null的结果为object， null在js中是一种特殊的对象，而非等同于 undefined null 和 undefined 并不是等价的 var tmp = null; // 虽然tmp是null，但我也定义了 var undef; //声明但没定义 alert(typeof tmp); // object alert(typeof undef); // undefined 所以判断一个值是不是null的时候直接用 tmp == null即可，切勿使用typeof，null是一种特殊的对象 // 标量 // typeof 123; // number typeof 'string'; // string typeof true; // boolean // 函数 // typeof function(){}; //function // 对象 // typeof new String('string');

Why is SwingWorker not returning an object to the EDT?

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问题 I am using the SwingWorker class to perform a background task. Many different components of the GUI get updated after the background thread has done is job (these are in the done() method). The doInBackground() method publishes a HeatMap class object and the process() method adds it to a JPanel component. I have added MouseListener and MouseMotionListener to this Heatmap class object. The mouseMoved() method is present in the main GUI class. When the mouse is moved, the coordinate position of

Why is SwingWorker not returning an object to the EDT?

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String subscript out of range. String size is unknown and looping string until null

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问题 #include<iostream> #include<cmath> #include<iomanip> #include<string> using namespace std; int main() { string word; int j = 0; cin >> word; while(word[j]){ cout << "idk"; j++; } cout << "nope"; system("pause"); return 0; } This is just a little trial program to test this loop out. The program I am working on is about vowels and printing vowels out from a sequence determined by the user. The string isn't defined until the user types in. Thank you for your guys help in advance. 回答1: Try this

Why is FileReader.readAsText() returning null?

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问题 I am trying to read a file in the same directory of an HTML and JavaScript file however it seems to be returning null. Below I have added the code I have from each file. HTML File: <html>  <body> <div class="content"> <div id="googleMap"></div> <div id="right_pane_results">hi</div> <div id="bottom_pane_options"> <button onclick="get_parameters()">Try It</button> </div> </div> </body> <script type="text/javascript" src=".

what is a null pointer in c

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问题 #include <stdio.h> int main(void) { struct findEntry { int value; struct entry *next; }; struct entry n1, n2, n3; struct entry *list_pointer = &n1; n1.value = 100; n1.next = &n2; n2.value = 200; n2.next = &n2; n3.value = 300; n3.next = (stuct entry *) 0; while (list_pointer != (struct entry *)0) { printf("%i\n", list_pointer->value); list_pointer = list_pointer->next; } return 0; } I don't understand what the syntax (struct entry *) 0 , means here. In the book I am reading it says it is a