All Questions

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them? What methods/tools can be used to determine the cause so that you stop the exception from causing the program ...

I have a function foo which makes an Ajax request. How can I return the response from foo? I tried returning the value from the success callback as well as assigning the response to a local variable ...

When discussing performance with colleagues, teaching, sending a bug report or searching for guidance on mailing lists and here on Stack Overflow, a reproducible example is often asked and always ...

If user input is inserted without modification into an SQL query, then the application becomes vulnerable to SQL injection, like in the following example: $unsafe_variable = $_POST['user_input']; ...

I need to match all of these opening tags: <p> <a href="foo"> But not these: <br /> <hr class="foo" /> I came up with this and wanted to make sure I've got it right. I am ...

I have some code and when it executes, it throws a NullReferenceException, saying: Object reference not set to an instance of an object. What does this mean, and what can I do to fix this error?

I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug. Is == bad? When should it ...

I'm running a PHP script, and continue to receive errors like: Notice: Undefined variable: my_variable_name in C:\wamp\www\mypath\index.php on line 10 Notice: Undefined index: my_index C:\wamp\...

What are the technical reasons for why one shouldn't use mysql_* functions? (e.g. mysql_query(), mysql_connect() or mysql_real_escape_string())? Why should I use something else even if they work on ...

This question attempts to collect the few pearls among the dozens of bad C++ books that are published every year. Unlike many other programming languages, which are often picked up on the go from ...

Everyone runs into syntax errors. Even experienced programmers make typos. For newcomers it's just part of the learning process. However, it's often easy to interpret error messages such as: PHP ...

Consider the following code: 0.1 + 0.2 == 0.3 -> false 0.1 + 0.2 -> 0.30000000000000004 Why do these inaccuracies happen?

var funcs = []; for (var i = 0; i < 3; i++) { // let's create 3 functions funcs[i] = function() { // and store them in funcs console.log("My value: " + i); // each should log ...

What are undefined reference/unresolved external symbol errors? What are common causes and how to fix/prevent them? Feel free to edit/add your own.

In this question, someone suggested in a comment that I should not cast the result of malloc, i.e. int *sieve = malloc(sizeof(int) * length); rather than: int *sieve = (int *) malloc(sizeof(int) * ...

I have a bit of code where I am looping through all the select boxes on a page and binding a .hover event to them to do a bit of twiddling with their width on mouse on/off. This happens on page ready ...

I am trying to select data from a MySQL table, but I get one of the following error messages: mysql_fetch_array() expects parameter 1 to be resource, boolean given or mysqli_fetch_array() ...

What is this? This is a number of answers about warnings, errors and notices you might encounter while programming PHP and have no clue how to fix. This is also a Community Wiki, so everyone is ...

When running my script, I am getting several errors like this: Warning: Cannot modify header information - headers already sent by (output started at /some/file.php:12) in /some/file.php on line 23 ...

<?php $name = $_POST['name']; $email = $_POST['email']; $message = $_POST['message']; $from = 'From: yoursite.com'; $to = 'contact@yoursite.com'; $subject = 'Customer ...

I have a constructor function which registers an event handler: function MyConstructor(data, transport) { this.data = data; transport.on('data', function () { alert(this.data); ...

I am trying to learn the best way to write queries. I also understand the importance of being consistent. Until now, I have randomly used single quotes, double quotes, and back ticks without any real ...

I'm setting up a new server, and want to support UTF-8 fully in my web application. I have tried in the past on existing servers and always seem to end up having to fall back to ISO-8859-1. Where ...

I've heard much about the understandable abhorrence of using .Select in Excel VBA, but am unsure of how to avoid using it. I am finding that my code would be more re-usable if I were able to use ...

I always thought Java was pass-by-reference. However, I've seen a couple of blog posts (for example, this blog) that claim that it isn't. I don't think I understand the distinction they're making. ...

How can one parse HTML/XML and extract information from it?

Given the following examples, why is outerScopeVar undefined in all cases? var outerScopeVar; var img = document.createElement('img'); img.onload = function() { outerScopeVar = this.width; }; ...

What is this? This is a collection of common Q&A. This is also a Community Wiki, so everyone is invited to participate in maintaining it. Why is this? regex is suffering from give me ze code ...

Quote from The C++ standard library: a tutorial and handbook: The only portable way of using templates at the moment is to implement them in header files by using inline functions. Why is this? (...

Is there an SQL injection possibility even when using mysql_real_escape_string() function? Consider this sample situation. SQL is constructed in PHP like this: $login = mysql_real_escape_string(...

I'm adding this question because I'm new to Java and Android and I searched for hours trying to figure this out. The answer came from a combination of related answers, so I figured I'd document what I ...

I got an error while running my Android project for RssReader. Code: URL url = new URL(urlToRssFeed); SAXParserFactory factory = SAXParserFactory.newInstance(); SAXParser parser = factory....

I have a nested data structure containing objects and arrays. How can I extract the information, i.e. access a specific or multiple values (or keys)? For example: var data = { code: 42, ...

What does copying an object mean? What are the copy constructor and the copy assignment operator? When do I need to declare them myself? How can I prevent my objects from being copied?

I just found a comment in this answer saying that using iostream::eof in a loop condition is "almost certainly wrong". I generally use something like while(cin>>n) - which I guess implicitly ...

How would you explain JavaScript closures to someone with a knowledge of the concepts they consist of (for example functions, variables and the like), but does not understand closures themselves? I ...

Is there a plugin-less way of retrieving query string values via jQuery (or without)? If so, how? If not, is there a plugin which can do so?

What are the possible reasons for document.getElementById, $("#id") or any other DOM method / jQuery selector not finding the elements? Example problems include: jQuery silently failing to bind an ...

I'm developing an application which displays images, and plays sounds from a database. I'm trying to decide whether or not to use a separate JFrame to add images to the database from the GUI. I'm ...

I've seen people trying to read files like this in a lot of posts lately. Code #include <stdio.h> #include <stdlib.h> int main(int argc, char **argv) { char * path = argc > 1 ? ...

I've been told by others that writing using namespace std in code is wrong, and that I should use std::cout and std::cin directly instead. Why is using namespace std considered a bad practice? Is it ...

I am developing an application, and everytime I run it, I get the message: Unfortunately, MyApp has stopped. What can I do to solve this? About this question - obviously inspired by What is a ...

I have this code: <script type="text/javascript"> var foo = 'bar'; <?php file_put_contents('foo.txt', ' + foo + '); ?> var baz = <?php echo 42; ?>; ...

What does ArrayIndexOutOfBoundsException mean and how do I get rid of it? Here is a code sample that triggers the exception: String[] name = {"tom", "dick", "harry"}; for(int i = 0; i<=name....

I am using the Scanner methods nextInt() and nextLine() for reading input. It looks like this: System.out.println("Enter numerical value"); int option; option = input.nextInt(); // Read ...

I have noticed that there doesn't appear to be a clear explanation of what the this keyword is and how it is correctly (and incorrectly) used in JavaScript on the Stack Overflow site. I have ...

I have the following code. #include <iostream> int * foo() { int a = 5; return &a; } int main() { int* p = foo(); std::cout << *p; *p = 8; std::cout << ...

I'm trying to make a function that will compare multiple variables to an integer and output a string of three letters. I was wondering if there was a way to translate this into Python. So say: x = 0 ...

In templates, where and why do I have to put typename and template on dependent names? What exactly are dependent names anyway? I have the following code: template <typename T, typename Tail> //...

Anyone tinkering with Python long enough has been bitten (or torn to pieces) by the following issue: def foo(a=[]): a.append(5) return a Python novices would expect this function to always ...