I have a code like this  class Base { public:     Base() {}; };  class Derived : public Base { public:     Derived() {cout &lt;&lt; "Derived" &lt;&lt; endl;} };  int main() {     Derived a(); // Only called base constructor     Derived b;   // called derived constructor }   What is the difference between these two calls? My understanding is that base constructor is always called before derived constructor? Why is the derived constructor skipped?  Thanks,
Is there any good reason that an empty set of round brackets (parentheses) isn't valid for calling the default constructor in C++?  MyObject  object;  // ok - default ctor MyObject  object(blah); // ok  MyObject  object();  // error   I seem to type "()" automatically everytime. Is there a good reason this isn't allowed?
How do you access browser history? Some e-Marketing tools claim to choose which web page to display based on where you were before. That is, if you've been browsing truck sites and then go to Ford.com, your first page would be of the Ford Explorer.  I know you can get the immediate preceding page with HTTP_REFERRER, but how do you know where they were 6 sites ago? Database does not update automatically with MySQL and Python I'm having some trouble updating a row in a MySQL database. Here is the code I'm trying to run:  import MySQLdb  conn=MySQLdb.connect(host="localhost", user="root", passwd="pass", db="dbname") cursor=conn.cursor()  cursor.execute("UPDATE compinfo SET Co_num=4 WHERE ID=100") cursor.execute("SELECT Co_num FROM compinfo WHERE ID=100") results = cursor.fetchall()  for row in results:     print row[0]  print "Number of rows updated: %d" % cursor.rowcount  cursor.close() conn.close()   The output I get when I run this program is:     4Number of rows updated: 1   It seems like it's working but if I query the database from the MySQL command line interface (CLI) I find that it was not updated at all. However, if from the CLI I enter UPDATE compinfo SET Co_num=4 WHERE ID=100; the database is updated as expected.  What is my problem? I'm running Python 2.5.2 with MySQL 5.1.30 on a Windows box. Can you identifiy this short about teenagers on a raft getting swallowed up by an oil slick? Finding Zero Divisors and Units of Rings $\mathbb{Z}_n \times \mathbb{Z}_m$ Fast way of copying IMAP to IMAP on CentOS I'm trying to copy of IMAP emails from one server to my new server but after Googling for hours and trying several tools, nothing is working. Is there a tool that actually works?  I am copying hundreds of thousands of emails so using a email client is out of the question, I tried it, and at the rate of a email per 2 seconds, it would take a few weeks or months!  www.linux-france.org/prj/imapsync/ is commonly mentioned, however, the tool is no longer available.  I tried www.athensfbc.com/imap_tools/ which just hangs and does nothing.  Any migration tools that work? Help me to solve this problem please..  Let $Y_{(1)}, Y_{(2)}, Y_{(3)}, Y_{(4)}, Y_{(5)}$ denote the order statistics of a random sample of size 5 from a distribution having p.d.f. $f(y) = e^{(-y)}, 0 &lt; y &lt; \infty$, zero elsewhere. Show that $Z_1 = Y_{(2)}$ and $Z_2 = Y_{(4)} − Y_{(2)}$  are independent. Hint: First find the joint p.d.f. of $Y_{(2)}$  and  $Y_{(4)}$. How to find out if an item is present in a std::vector? All I want to do is to check whether an element exists in the vector or not, so I can deal with each case.  if ( item_present )    do_this(); else    do_that(); Order of an element in a finite cyclic group I need to prove that if $f: (0,1) \rightarrow \mathbb{R}$ is Uniformly continuous then it is  bounded.   Thank you. How can I remap a keyboard key? Quotient rings of Gaussian integers I'm trying to identify a song by a female 80's pop group.   Here are the lyrics I remember:     It's the story of my life if you want to know   a play where everything is meant to be   you're the story of my life and I can't let you go How do I lerp between values that loop (such as hue or rotation)? I'm trying to make the joint rotate smoothly around the center of the canvas, toward the angle of mouse pointer. What I have works, but I want it to animate the shortest distance possible to get to the mouse angle. The problem occurs when the value loops around at the horizontal line (3.14 and -3.14). Mouseover that area to see how the direction switches and it takes the long way back around.  Relevant Code   // ease the current angle to the target angle joint.angle += ( joint.targetAngle - joint.angle ) * 0.1;  // get angle from joint to mouse var dx = e.clientX - joint.x,     dy = e.clientY - joint.y;   joint.targetAngle = Math.atan2( dy, dx );   How can I make it rotate the shortest distance, even "across the gap"? Meaning of syntax $N(\mathbf{y} \mid \mathbf{0}, \mathbf{K})$ (multivariate normal distribution) Can I prevent others from editing my question? edited my question,  where I specifically said that our software sending back stacktrace to one of our servers was a user-known public feature.  He then modified the title of my post, along with the entire content, making it sound like I snuck in the feature and that our application was phoning home without our users knowing.    I specifically wrote in the original post that the feature was not sneaky. He completely changed the meaning of my post. I find this to be rather unacceptable.  A few questions:   Is it possible to prevent editing of my posts? How can I retaliate? Can I file a complaint?   Can people with  do anything they want on Stack Overflow? Mysql: Select rows from a table that are not in another I would like to install Ubuntu 14.04.02 LTS on my machine which currently has Mageia 4.1.   So, I have the following partitions: One for /, one for swap and one for /home.   I have some important data on /home which I wouldn't like to lose (I have backed them up, but I would prefer to keep them) after a clean install. I plan to reformat partitions one and two as above and keep the /home one.   Will I be able to tell Ubuntu to do so during an installation? By this I mean: Will it be able to recognize the /home partition and keep all its data intact while formatting the rest? And one more question: Will it be able to keep the users as they are our will I be forced to change them too? (I have the bad feeling that it won't be able to keep the users as they are...) Solve the following equation: $\sqrt {\sin x - \sqrt {\cos x + \sin x} } = \cos x$ Solve the following equation:  \begin{array}{l}{\sqrt{\sin x-\sqrt{\cos x+\sin x}}=\cos x} \\ \text{my try as follows:}\\{\sin x-\sqrt{\cos x+\sin x}=\cos ^{2} x} \\ {\sin x-\cos ^{2} x=\sqrt{\cos x+\sin x}} \\ {\sin ^{2} x+\cos ^{4} x-2 \sin x \cos ^{2} x=\cos x+\sin x} \\ {\sin ^{2} x+\cos ^{4} x-2 \sin x \cos ^{2} x-\cos x-\sin x=0} \\ {\sin ^{2} x+\cos ^{4} x-2 \sin x\left(1-\sin ^{2} x\right)-\cos x-\sin x=0} \\{\sin ^2}x + {\left( {1 - {{\sin }^2}x} \right)^2} - 2\sin x\left( {1 - {{\sin }^2}x} \right) - \cos x - \sin x = 0\\ {\sin ^{2} x+\sin ^{4} x-2 \sin ^{2} x+1-2 \sin x+2 \sin ^{3} x-\cos x-\sin x=0} \\ {\sin ^{4} x+2 \sin ^{3} x-\sin ^{2} x-3\sin x-\cos x+1=0}\end{array}  Now i think it gets more complicated , any help would be appreciated How to have a figure with caption in multicol environment? I am having the following problem with adding a figure inside the multicol environment:  \documentclass[10pt, twoside]{book} \usepackage{graphicx} \usepackage{subfig}  \begin{document}   \begin{multicols}{2}  a test file for picture inclusion along with the captions and labeling \begin{figure}  \centering  \includegraphics[width=5cma]{Cauchy_sequence_illustration-png}\\  \caption{Lets see}\label{pinki} \end{figure} \end{multicols}  \begin{figure}  \centering   \includegraphics[width=5cm]{Cauchy_sequence_illustration-png}\\  \caption{Lets see}\label{pinki} \end{figure}    \end{document}    After this while I am pressing Ctrl + Shift + X (usually I compile like this in DVI format and then clicking "dvi--->pdf" I convert it into PDF document.) the picture in multicol environment is not shown in YAP Viewer but the second one (which is outside of multicol environment) is shown along with the caption.  Kindly help me how to handle this problem. Please note that I am using the figure in .ps format. And I am not allowed to use any other format according to the instruction. Summoning an item in 1.9 with motion When I put   /summon Item ~ ~2 ~ {Item:{id:"minecraft:diamond",Count:1b,Motion:[0.0,0.8,0.0]}}    in a command block, it summons the diamond with Count:1b but it doesn't follow the Motion Tag. Does anyone know how to get the Motion Tag working?