need to call the base destructor method from a derived class in c++?
Do I need to explicitly call the base virtual destructor?
When I install a simple program it often uses make &amp;&amp; make install and doesn't often even have an uninstall target.  If I wish to upgrade a program, is it standard protocol to assume it just rewrites seamlessly over the old program?  How do I keep track of these programs; do most people just 'fire and forget' and if no uninstall target is given do I have to manually delete everything? QGIS update from 2.14 to 2.16 failed on Ubuntu 14.04 Until yesterday my whole qgis and python-qgis worked fine with version 2.14 under Ubuntu 14.04. After a simple sudo apt-get update and sudo apt-get upgrade qgis failed to update... Several attempts to reinstall it with different versions failed.  Current error message (for version 2.14.3) goes like this:  qgis-providers (2.14.3+dfsg-2~trusty1) is configured ... /usr/lib/qgis/crssync: symbol lookup error: /usr/lib/libgdal.so.20: undefined symbol: GEOSDelaunayTriangulation_r   I also tried to reinstall all gdal libraries - not sure if I got all?!  Maybe it is somehow related to this one:  ?  UPDATE:  Trying to install version 2.16.0 it gives different but similar error:  /usr/lib/qgis/crssync: symbol lookup error: /usr/lib/libqgis_core.so.2.16.0: undefined symbol: GEOSNearestPoints_r   UPDATE Sources:  For version 2.16.0 there are these sources in /etc/apt/sources.list:  deb http://qgis.org/debian trusty main deb-src http://qgis.org/debian trusty main deb http://qgis.org/debian trusty main deb-src http://qgis.org/debian trusty main   which are all the same, right?   When I do apt-cache policy qgis it gives me:  qgis:   Installiert:           1:2.16.0+20trusty   Installationskandidat: 1:2.16.0+20trusty   Versionstabelle:  *** 1:2.16.0+20trusty 0         500 http://qgis.org/debian/ trusty/main amd64 Packages         100 /var/lib/dpkg/status      2.0.1-2build2 0         500 http://de.archive.ubuntu.com/ubuntu/ trusty/universe amd64 Packages How do you serialize an object in C++? I have a small hierarchy of objects that I need to serialize and transmit via a socket connection.  I need to both serialize the object, then deserialize it based on what type it is.  Is there an easy way to do this in C++ (as there is in Java)?  Are there any C++ serialization online code samples or tutorials?  EDIT: Just to be clear, I'm looking for methods on converting an object into an array of bytes, then back into an object.  I can handle the socket transmission. How can one prove the Bohr-Sommerfeld quantization condition $$ \oint p~dq ~=~2\pi n \hbar $$ from the WKB ansatz solution $$\Psi(x)~=~e^{iS(x)/ \hbar}$$ for the Schroedinger equation? With $S$ the action of the particle defined by Hamilton-Jacobi equation $$ \frac{\partial S}{\partial t}+ \frac{(\nabla S)^{2} }{2m}+V(x)~=~0 .$$ My java code has an obvious error. Why does it compile and run? I've posted a lot to StackOverflow, and I've noticed something kind of irritating with the formatting in writing questions and comments. If I need to put something inside a &lt; and a >, without spaces in the middle (like right there), it will think it's code and not show up, like this   (obviously it won't come up what I wrote there, or else this wouldn't be an issue, but if you open up the question to edit you can see what's written there.)  If I want it to show up, right now I have to add an extra set of brackets inside of the originals with a junk variable, like right &lt;here> (again, open in edit window to see).  This is really annoying when trying to show variables like lists that require those brackets, and I feel like the junk variables could confuse people looking at the edits. Is there a way to get around this formatting? Thanks! What is a suitable image resolution for canvas prints? I would like to create a 60 inch x 20 inch canvas print using an image with a resolution of 4759x1798 (240 pixels per inch) and I would like to know if the image quality will still be good at that size.  To generalise the question, what is the recommended maximum size of an enlargement at varying image resolutions?  e.g. 3 megapixel, 5 megapixel, 8 megapixel, etc What is the preferred way to remove spaces from a string in C++? I could loop through all the characters and build a new string, but is there a better way? Is there a way to follow a particular person (or List&lt;Person&gt;) easily? Some people answer the questions in a very educative way, and I don't want to miss them. How do I show that:  $$\frac{1}{\sin^{2}\frac{\pi}{14}} + \frac{1}{\sin^{2}\frac{3\pi}{14}} + \frac{1}{\sin^{2}\frac{5\pi}{14}} = 24$$  This is actually problem B $4371$ given at this . Looks like a very interesting problem.   My attempts: Well, I have been thinking about this for the whole day, and I have got some insights. I don't believe my insights will lead me to a $\text{complete}$ solution.   First, I wrote $\sin\frac{5\pi}{14}$ as $\sin\frac{9 \pi}{14}$ so that if I put $A = \frac{\pi}{14}$ so that the given equation becomes, $$\frac{1}{\sin^{2}{A}} + \frac{1}{\sin^{2}{3A}} + \frac{1}{\sin^{2}{9A}} =24$$ Then I tried working with this by taking $\text{lcm}$ and multiplying and doing something, which appeared futile. Next, I actually didn't work it out, but I think we have to look for a equation which has roots as $\sin$ and then use $\text{sum of roots}$ formulas to get $24$. I think I haven't explained this clearly.         $\text{Thirdly, is there a trick proving such type of identities using Gauss sums ?}$ One post related to this is:  I don't know how this will help as I haven't studied anything yet regarding Gauss sums. Unable to change payment information to NONE in iOS Appstore Embed .mov file via 'Add Media' not working Fastest method to determine my PC's IP address (Windows) This may seem trivial but I'm looking for the quickest method to determine my PC's IP address within my network.   This changes regularly as I connect from one network to the next via DHCP The connection changes from wired to wireless Windows 7 PC (although ideally the perfect solution would work on all versions of Windows) Various adapters installed (e.g. VMWare, Tunnels, etc.)   I need to know this as I often run a local web server where I need to access files over the local network... and since it changes regularly I want the fastest method to retrieve the address.  My current flow is:   WindowsKey + R to open the Run dialog "cmd" + Enter to open a command prompt "ipconfig" + Enter to get the diagnostics info Scroll to or resize the window so that I can see the line in my Ethernet adapter Local Area Connection for my ipv4 Address Remember it to type elsewhere... or  Right click > select Mark > highlight the address > press Enter to copy it to the clipboard   This wasn't so bad with Windows XP when I had no additional adapters, tunnels, wireless connections etc. but the amount of data returned with this command makes it hard to pluck out.  Surely there must be a better, faster way! (bonus points if adding it to the clipboard is easily accomplished) Stern-Brocot tree where each node has two fathers Given $n$ independent geometric random variables $X_n$, each with probability parameter $p$ (and thus expectation $E\left(X_n\right) = \frac{1}{p}$), what is $$E_n = E\left(\max_{i \in 1 .. n}X_n\right)$$    If we instead look at a continuous-time analogue, e.g. exponential random variables $Y_n$ with rate parameter $\lambda$, this is simple: $$E\left(\max_{i \in 1 .. n}Y_n\right) = \sum_{i=1}^n\frac{1}{i\lambda}$$  (I think this is right... that's the time for the first plus the time for the second plus ... plus the time for the last.)  However, I can't find something similarly nice for the discrete-time case.    What I have done is to construct a Markov chain modelling the number of the $X_n$ that haven't yet "hit". (i.e. at each time interval, perform a binomial trial on the number of $X_n$ remaining to see which "hit", and then move to the number that didn't "hit".) This gives $$E_n = 1 + \sum_{i=0}^n \left(\begin{matrix}n\\i\end{matrix}\right)p^{n-i}(1-p)^iE_i$$ which gives the correct answer, but is a nightmare of recursion to calculate. I'm hoping for something in a shorter form. Alpha and Omega limit sets (dynamical systems) What are all the possible $α$- and $ω$-limit sets of points for the linear system of equations $x'=Ax$ given by the following matrices $A$:  I guess I don't really know how to get started, Could I have some guidance? So I was told to calculate the eigenvalues (fine) and eigenvectors (I kind of forgot how to do that...)  I know that the $ω$-limit sets of points are the set of points that the system of equation approach as time goes to infinity, and the $α$-limit sets of points are the points approached as t goes to negative infinity.   $    A=   \left[ {\begin{array}{cc}    -4 &amp; -2 \\    3 &amp; 11 \\   \end{array} } \right] $   $λ_1=-10$ $λ_2=-5$  Since both eigenvalue are negative, this is a stable node, and the $ω$-limit set=0.  for $λ_1=-10$:  eigenvector $    =   \left[ {\begin{array}{cc}   1 \\    3 \\   \end{array} } \right] $  for $λ_2=-5$:  eigenvector $    =   \left[ {\begin{array}{cc}   2 \\    1 \\   \end{array} } \right] $   $    A=   \left[ {\begin{array}{cc}    1 &amp; 1 \\    3 &amp; 1 \\   \end{array} } \right] $   $λ_1=4$ $λ_2=-2$  Since one eigenvalue is positive and one is negative, it is not stable, so I can't use the same reasoning that I used above to find the $ω$-limit set... so I am not sure how to continue  for $λ_1=4$:  eigenvector $    =   \left[ {\begin{array}{cc}   1 \\    1 \\   \end{array} } \right] $  for $λ_2=-2$:  eigenvector $    =   \left[ {\begin{array}{cc}   -1 \\    1 \\   \end{array} } \right] $   $    A=   \left[ {\begin{array}{cc}    4 &amp; 5 \\    -5 &amp; -2 \\   \end{array} } \right] $   $λ_1=1+4i$ $λ_2=1-4i$  for $λ_1=1+4i$:  eigenvector $    =   \left[ {\begin{array}{cc}   -3/5-(4i)/5 \\    1 \\   \end{array} } \right] $  for $λ_1=1-4i$:  eigenvector $    =   \left[ {\begin{array}{cc}   -3/5+(4i)/5 \\    1 \\   \end{array} } \right]$ "No such file or directory" when trying to remove a file, but the file exists? A screen of mine burnt out, and was replaced with a screen of lower resolution. It works in safe mode as that is in 800x600 resolution, but when I try to boot to normal mode, it fails. Is there a way to change the resolution for normal mode in safe mode? Is "Five dollars is all I have" correct? I want to emphasize that I only have 5 dollars, so can I use the sentence:     Five dollars is all I have.   Or must it be:      Five dollars are all I have.   Please give the explanation as well. Example of a ring with an infinite inclusion chain of ideals I'm trying to track down an example of a ring in which there exists an infinite chain of ideals under inclusion. (i.e. $I_1 \subsetneq I_2 \subsetneq I_3 \subsetneq...$)