LNK2019 error on destructor and "factory" method I am getting an unresolved external symbol error (LNK2019, which seems timely given the current year) on the destructor and a static "factory" method that returns a unique_ptr of a class (see code below).  #ifndef ABC_HPP #define ABC_HPP  #include &lt;memory&gt;  enum SomeEnum { TYPE_A, TYPE_B };  template &lt;SomeEnum Type&gt; class ABC { //------------------------------------------------------------------------------ Constructor / Destructor private:      ABC();      /* Inaccessible Methods */     ABC(ABC&amp;&amp;)                  = delete;     ABC(const ABC&amp;)             = delete;     ABC&amp; operator=(ABC&amp;&amp;)       = delete;     ABC&amp; operator=(const ABC&amp;)  = delete;  public:     ~ABC();  //------------------------------------------------------------------------------ Factory Method public:      static std::unique_ptr&lt;ABC&lt;Type&gt;&gt; Create();  //------------------------------------------------------------------------------ };  #endif /* ABC_HPP */    Here is the implementation of the above class:  #include "ABC.hpp"  //------------------------------------------------------------------------------ Constructor(s)  template &lt;SomeEnum Type&gt; ABC&lt;Type&gt;::ABC() {}  //------------------------------------------------------------------------------ Destructor  template &lt;SomeEnum Type&gt; ABC&lt;Type&gt;::~ABC() {}  //------------------------------------------------------------------------------ Create  template &lt;SomeEnum Type&gt; std::unique_ptr&lt;ABC&lt;Type&gt;&gt; ABC&lt;Type&gt;::Create() {     return std::make_unique&lt;ABC&lt;Type&gt;&gt;(); }  //------------------------------------------------------------------------------    Everything compiles nice and fine... until I do this:  #include "ABC.hpp"  int main(int argc, char* argv[]) {     auto thingA = ABC&lt;TYPE_A&gt;::Create();      return 0; }   I originally tried to compile it on Visual Studio, but I also tried clang and got the same error.  What exactly am I doing wrong here? I feel like I've run into this error before but that I'm just too dumb to remember what the problem was.  I can get rid of the destructor error if I use raw pointers, but I want to use unique_ptr here. I can also get rid of it by simply commenting out the destructor entirely, but that's not cool with me either. Another way is to have the destructor defined within the header, but that's silly; I should be able to separate the implementation.  So far I have not found a way to get the Create method to work. Am I just trying to do too much here? Do I actually have to make a factory class? Am I too much of a dreamer? Is this question too long???  Thanks in advance to anyone who responds. :)
Why can templates only be implemented in the header file? Quote from :     The only portable way of using templates at the moment is to implement them in header files by using inline functions.   Why is this?  (Clarification: header files are not the only portable solution. But they are the most convenient portable solution.)
Low budget alien movie about the Earth being cooked I’m looking for an alien movie I watched years ago, mid to late 2000’s about the Earth being cooked or heated up by aliens. The poster is a reflection of the Earth heating up with an orange glow on an aliens eye. It was a low budget movie and I think the one I watched was pirated from China. Again low budget, bad quality and the name could’ve been something worthy he word scorch or something like that. The alien in the movie had legs with knees that went inwards and it had red eyes. Show that if $f$ is integrable on $[a, b]$ then $\lvert f \rvert$ is also integrable. Hint: Show that $$U (P , \lvert f \rvert) − L(P , \lvert f \rvert) ≤ U (P , f ) − L(P , f ).$$ I have: $$U (P , \lvert f \rvert) \ge U (P , f )$$ and $$ L(P , \lvert f \rvert) \ge L(P,f)$$ Thus, $$U (P , \lvert f \rvert) − L(P , \lvert f \rvert) ≤ U (P , f ) − L(P , f ).$$ So I integrate the holomorphic function $\frac{e^{iz} -1}{iz}$ over the half disk in the upper half plane, let me name it $\Gamma$. By using Cauchy's theorem, it equals 0.  $$0 = \int_{\Gamma} \frac{e^{iz} -1}{iz} = \int_{0}^{\pi}(e^{iRe^{i\theta}}-1)d\theta + \int_{-R}^{R} \frac{e^{it}-1}{it}dt$$  ($Re^{[0, \pi]}$ and $t: [-R, R]$ being the respective parametrizations.)  By splitting the left integral in two, I get $\int_{0}^{\pi} e^{iRe^{i\theta}}d\theta \rightarrow 0$ by dominated convergence, and $\int_{0}^{\pi} -1d\theta = -\pi$. By making $R \rightarrow \infty$, I'm left with  $$\pi = \int_{-\infty}^{\infty} \frac{e^{it} - 1}{it}dt = \int_{-\infty}^{\infty}\frac{\sin t}{t}dt + \int_{-\infty}^{\infty}\frac{\cos t -1}{it}dt.$$  How do I get rid of the integral on the right? I welcome all feedback. Mechanics of Horizontal Stretching and Shrinking I know $y=2f(x)$ doubles the $y$ value in vertical shifting, and I know that $y=(1/2)f(x)$ halves the $y$ value. But, why does $y=f(2x)$ halve the $x$ value, and why does $y=f((1/2)x)$ double the $x$ value in horizontal shifting? I looked at the graphs, and I see the difference, but I want to know the math behind why it halves instead of doubling the $x$ value for $y=f(2x)$. Maybe this is a stupid question, but could someone help me out?  Thank you. Omission of the indefinite article to eliminate ambiguity love between husband and wife   What is the reason that there is no article (e.g. "love between a husband and a wife") in the above? Has some kind of a rule been identified grammatically when it comes to such a case? If I were to guess I think it's because the indefinite article 'a', the purpose of that, is taking a generic sample (or 'instance') from a 'class' (the class of husbands), but in the above sentence you want to refer to the class itself... the husband class and the wife class... and not an 'instance' of them, because it just is more to the point. Do you think this is a fair reasoning? Also, a thought came to me that with the use of the indefinite article, you get a generic husband and a generic wife, which, may not necessarily love each other (for they are not a specific pair of a specific husband and a specific wife who in fact love each other). How do I get rid of eggs? Let $p$ be a prime number . The order of a $p$-Sylow subgroup of the group $GL_{50}(F_p)$ of invertible $50\times50$ matrices with entries from the finite field $F_p$,equals which of the following    1.$p^{50}$ 2.$p^{125}$ 3.$p^{1250}$ 4.$p^{1225}$    I think order of this  group is $p^{2500}$  .A  sylow p-subgroup of order $P^k$ divides  order of the group but $p^{k+1}$  does not. I confused here how to apply these things . After the  of registering an account to book train tickets online using my British VISA card, I finally got into a position of being able to book a ticket, but what it appears to be telling me is that I'm only being added to a wait list, which I assume means my tickets aren't confirmed.  Can someone explain how the wait list works, and what my chances are of getting on the train successfully?    It currently says the wait list is 7 The train is the Mandor Express, from Delhi to Jodhpur on the 18th of Nov   Update: So I got the train! Although it didn't get confirmed until a few hours before it was due to leave. Is there any uncountably infinite set that does not generate the reals? Does there exist an uncountably infinite set $X \subseteq \mathbb R$ such that $\mathbb R \neq \left&lt;X\right&gt;$? I can't think of any, but I'm also having trouble trying to prove that no such subset exists.  For example: $\mathbb R$ is uncountable and obviously $\mathbb R = \left&lt;\mathbb R\right&gt;$. The Cantor set $C$ is uncountable, and we know that $C - C = [0, 1]$, so then since $\mathbb R = \left&lt;[0, 1]\right&gt;$ we know that $C$ also generates $\mathbb R$. Also the set of irrationals $\mathbb R \setminus \mathbb Q$ is uncountable, but we can generate all the rational numbers by fixing one irrational number $\alpha$ and then saying the any rational number $x$ shall be $(\alpha + x) - \alpha$, since both $\alpha + x$ and $\alpha$ are irrational.  So the examples that quickly come to mind all generate the reals. Is there a simple counterexample? How to use if-else option in JSTL Why should edits be at least six non-space characters? Earlier today I got this message:  Oops! Your edit couldn't be submitted because:   Edits must be at least 6 non-space characters; is there something else to improve in this post?   However, the purpose of my edit was to change the formatting for a message to show code.  There may have been other grammatical mistakes that could have been, but in general it is possible that there would not be.  What's the correct protocol to handle a situation like this? How do I compare version numbers in Python? Delete questions/answers in iOS app There is currently no way to delete questions or answers in the iOS app, even with the required Trusted User privilege. We can edit and vote, but not delete.  Can this option please be added to the app? The Start menu no longer shows up when I press the Start button Programming pattern to generate VGA signal with micro-controller? I want to generate VGA signal with micro-controller (like TI Tiva ARM which runs at 90/120Mhz speed).  I'm not sure how to make accurate timings with micro-controller. Which programming pattern I need to use?  Do I need any inline assembler code? How to wisely use interrupts?  Would be great if anybody show some pseudo code how to generate VGA signal.  I successfully generated VGA signal with FPGA. But I just can't figure out how to do it with MCU. What are the minimum root filesystem applications that are required to fully boot linux? What is the path of an MTP device in Windows? I am running Windows XP and have a phone mounted through USB by MTP.  In Explorer, its address is:  My Computer\SAMSUNG-SGH-I547\Phone\DCIM   I would like to execute a command line command such as  explorer "My Computer\SAMSUNG-SGH-I547\Phone\DCIM\Camera"   so as to quickly go to the Camera folder. (Right-clicking the device or anything in it does NOT provide a "Create Shortcut" dialog.)  But "My Computer" is not a valid PATH in Windows. Unlike USB flash drives, it seems the phone mounted by MTP does not get a letter drive name.  So, what is the path of an MTP device in Windows?  If the answer is there is no command line path, is there workaround? Story about building up speed leading to increased quality of life It's a story I read in 2 or 3 parts in a Greek sci-fi magazine called 9 around 2004 (give or take a few years), but it may be a bit older than that. This is what I remember (and I hope it's all accurate):   The protagonist used to travel a lot, mainly using high speed media like aircraft. It was established in the story that as he traveled more frequently and with more speed, he would gradually cross over towards (sort of) higher planes of existence (and that everyone in the setting could do the same, although most people simply didn't bother). These higher planes of existence were apparently still Earth, but the environments and the inhabitants were increasingly more alien and life in them was increasingly luxurious. As far as I recall, the protagonist's goal was to reach those higher levels (either for the luxury or for some other reason I can't recall). If he failed to maintain his "speed" for too long, he would fall back to lower planes of existence, with more familiar characteristics and significantly lower quality of life. His wife had died some time ago and her grave was apparently in the lower planes. He did visit her once near the end of the story, before starting to build up "speed" again.   I don't happen to know the original language of the story because what I read was a version translated into Greek. Is there a way to view Google Chrome browsing history past three months ago? I'm trying to find a page I looked at months ago but it looks like it's disappeared off the face of the planet. I thought I would have better luck looking through my Google Chrome browsing history, but I can't see history past September. Can I force Google Chrome to display history further into the past? Can I retrieve the history manually from a directory? Is the history data gone? Edits that shadow a suggested edit inconsistently reject but include the suggestion