The following seems to be the recommended way to define a singleton in C++:  class Singleton { private:      Singleton();  public:     static Singleton &amp; get_instance() {         static Singleton instance;         return instance;     }       ~Singleton() {         // destructor      }      Singleton(Singleton const&amp;) = delete;     void operator=(Singleton const&amp;) = delete; }   Now, take this function:  void foo() {    Singleton &amp; s = Singleton::get_instance(); }   I expected the destructor to be called when the singleton instance goes out of scope in that function, but it's not. When does the destructor get called?
If a variable is declared as static in a function's scope it is only initialized once and retains its value between function calls. What exactly is its lifetime? When do its constructor and destructor get called?  void foo()  {      static string plonk = "When will I die?"; }
We want to show that if $a,b\in G$ where $G$ is a finite Abelian group, we have  $\operatorname{LCM}(|a|,|b|) = |ab|$ given that $ab \neq e$.   How I approached this question was by saying let $\operatorname{LCM}(|a|,|b|) = L$. Then if we show that $L$ divides $|ab|$ and $|ab|$ divides $L$ then $|ab| = L$. Showing that $|ab|$ divides $L$ was fine. But then I am having trouble with the second part that is showing $L$ divides $|ab|$. For this, so far I have:  Consider $(ab)^{|ab|} = e = a^{|ab|}b^{|ab|} $  since we know $a \neq b^{-1}$ by assumption then we can conclude that $|a|$ divides $|ab|$ and $|b|$ divides $|ab|$. We know that $L = \frac{|a||b|}{\operatorname{gcd}(|a|,|b|)}$ from here can we conclude that $L$ divides $|ab|$? What does "Perform GC" button do in jconsole? Gmail, how to forward email to group using a filter Since arrays and hashes can only contain scalars in Perl, why do you have to use the $ to tell the interpreter that the value is a scalar when accessing array or hash elements? In other words, assuming you have an array @myarray and a hash %myhash, why do you need to do:  $x = $myarray[1]; $y = $myhash{'foo'};   instead of just doing :  $x = myarray[1]; $y = myhash{'foo'};   Why are the above ambiguous?   Wouldn't it be illegal Perl code if it was anything but a $ in that place? For example, aren't all of the following illegal in Perl?  @var[0]; @var{'key'}; %var[0]; %var{'key'}; Research statement ideas got used by interviewing committee Range of A and null space of the transpose of A So I'm complete stuck with something. I know it the following statements are true (or at least the seem to be from the results that I got from messing around with it a bit on MATLAB), but I don't understand why they are true or how to show so. Let $A$ be and $m$X$n$ matrix. Show that:  a) if $x \in N(A^TA)$ then $Ax$ is in both $R(A)$ and $N(A^T)$.   For this one I messed around with it with my own examples and I got $Ax=0$, therefore satisfing the statement, but I don't understand what's actually going on.   b) $N(A^TA)=N(A)$  again, makes sense when I see the results in MATLAB, but don't undestand why it works.  c) $A$ and $A^TA$ have the same rank  d) If $A$ has linearly independent columns, the $A^TA$ is nonsingular.  For the last two I have no idea on how to even start showing the relationship. I feel like I'm missing some crucial relationship between $A$ and $A^TA$, but I'm just not seeing it.   I would greatly appreciate any help of sugestions on how to show that these statements are true.   Thank you very much. When I use the -a option as is asked and answered in , I got a lot of "rsync: failed to set permissions on" errors.  rsync: failed to set permissions on "/ata/text/RCS/jvlc,v": Operation not permitted (1) rsync: failed to set permissions on "/ata/text/RCS/jvm,v": Operation not permitted (1) rsync: failed to set permissions on ...   Why is this? The files are normal files with permission of 0664. After drinking an energy drink, there are little yellow and white bars above the health bar. What are those? What do they represent? How do you set password-hash for OpenLDAP? Detecting TCP Client Disconnect Resolving heteroscedasticity in Poisson GLMM How is evolution possible in contemporary humans? I would like to know if evolution is continuing to happen in modern humans, assuming things like existence of the nuclear family structure, fidelity to one partner, etc. It seems to me the answer would be NO because evolution depends on differential reproductive rates, but in the modern world, all male humans have roughly 2.5 (or whatever the number) kids. Add in the process of culturally modified selection pressure, and it seems to me that even an "unfit" male would end up having a couple of offspring. The fittest male (or female) is no better off than his or her contemporaries because of this "leveling" effect.   However, the impression I get from the popular science media is that scientists think evolution is continuing to happen. I would like to know what the actual scientific consensus is, and why. Thanks. Exact Duplicate:        I was reading an article on MSDN where I found a mention to google-fu. It says, “To search for C++ delimeters and code snippets is going to take a little Google-fu on the reader's part.” what does google-fu mean? Convert hex string to int in Python How do I convert a hex string to an int in Python?   I may have it as "0xffff" or just "ffff". How do I set up a "secure" open resolver? This is a  about securing public DNS resolvers   Open DNS servers seem pretty neat and convenient, as they provide IP addresses that we can use consistently across our company regardless of where they are located. Google and OpenDNS provide this functionality, but I'm not sure that I want these companies to have access to our DNS queries.  I want to set up something like this for use by our company, but I hear a lot about this being dangerous practice (particularly in regards to ) and I want to make sure that we do this right. What things do I need to keep in mind when building this type of environment? I have Ubuntu on my MacBook 2007 with a Spanish keyboard, on MacOS the @-sign was typed using Alt (Option) + 2, but on Ubuntu I have no idea. I have to copy and paste it every time. How do I type an at sign? How do I undo the most recent local commits in Git? There are often situations where buying two separate one-way tickets from A to C via B is cheaper than buying a normal multi-leg ticket. This can be especially useful with airlines such as Ryanair, which specifically avoids selling multi-leg tickets.  Is there a search engine which allows one to search for such flights? Under Windows, most applications and application data are stored in a special directory known as C:\Program Files (and occasionally C:\Program Files (x86)). What is the Ubuntu/Linux equivalent to this path? Is there even one? How to fix pagination for custom loops? I have added a custom/secondary query to a template file/custom page template; how can I make WordPress use my custom query for pagination, instead of using the main query loop's pagination?  Addendum  I have modified the main loop query via . Why isn't pagination working, and how do I fix it?