Class doesn't get defined. Linking error
Why can templates only be implemented in the header file?
Some common problems with displaying routes created from street data, such as bus routes, include:   Routes may overlap themselves, such as when a route takes the same road in opposite directions Routes may overlap other routes that take the same street. Routes are often overly detailed, or "noisy", owing to their derivation from street data. Indicating a route's direction unambiguously without overloading it with arrows can be a challenge.   What are some techniques for dealing with these issues in order to create a practical and usable route map, such as this ? Do you know of any such public transport maps that were produced by automatic techniques rather than manual illustration/digitization?  Specifically I am using ArcGIS 10, but solutions involving other software are welcome as well.  One technique I have had some success with for dealing with 1) is using ArcMap's  with a negative offset -- assuming the lines are oriented in the direction of travel, this will offset the lines such that the right and left-hand sides are distinct and oriented as you would expect (at least for  countries, for left-hand traffic countries one would use a positive offset). However the result tends to be a bit wonky around turns, interchanges and and U-turns, and is inflexible when dealing with multiple routes.  Another possibility that I am not very familiar with but which seems promising is  -- however, I have not had much luck in finding examples of using representations for transportation maps and whether it might fit the bill. 80's movie with a boy on skates or bmx bikes that has holographic ants that torture people Why does no one notice the Joker's presence as a policeman during the mayor's speech? Why are the solutions of polynomial equations so unconstrained over the quaternions? I was looking for proofs using Calculus for the area of a circle and come across this one $$\int 2 \pi r \, dr = 2\pi \frac {r^2}{2} = \pi r^2$$  and it struck me as being particularly easy. The only other proof I've seen was by a teacher and it involved integrating $x = \sqrt{r^2 - y^2}$ from $-1$ to $1$, using trig substitutions and then doubling the area to get $\pi r^2$ but the above proof seemed much more straight forward.  Is it a valid proof, or is it based on circular logic or some other kind of fallacy? External hard disk detection issue what exactly happened:  I have a Seagate 1 TB external hard disk.It was working fine till now.The problem started when I plugged it in my android phone and then back in my pc then simply it does not showup anywhere and :  It does not appear in file explorer   It does not appear in disk management   It is not listed in Diskpart command   It only appears in Device Manager under disk drives   It does not appear in BIOS  only makes sound when plugged and unplugged.  disk spins and light is also showing.   . What I already tried:   updated usb drivers.  used new cable also.  plugged in another pc  usb mass storage is also enabled in BIOS  no issue in any usb port  Anything else i can do? Django: How can I protect against concurrent modification of database entries Consider the sum of $n$ uniform distributions on $[0,1]$, or $Z_n$. Why does the cusp in the PDF of $Z_n$ disappear for $n \geq 3$? I've been wondering about this one for a while; I find it a little weird how abruptly it happens. Basically, why do we need just three uniforms for $Z_n$ to smooth out like it does? And why does the smoothing-out happen so relatively quickly?  $Z_2$:     $Z_3$:    (images shamelessly stolen from John D. Cook's blog: )  Why doesn't it take, say, four uniforms? Or five? Or...? Why do variable names often start with the letter 'm'? Isn't less just more? When I do more filename and less filename, it would seem that the resulting terminals are quite similar. I can navigate and search through my files identically (j, Space, /pattern, etc.).  I find it hard to believe that less is more and vice versa. Are there any differences between the two? What details should a good cover letter contain to back up a UK Visit Visa application? Command for taking a screenshot to a new file How to remove old device from Safari iCloud Tabs? I returned a MacBook to Apple Store, however apparently I forgot to sign out of iCloud and the latest tabs I was browsing still appear in Safari iCloud Tabs of my new MacBook and existing iPad.  I removed the device from icloud.com -> Find My iPhone but it didn't work. Tabs list from my old computer is still there and I am trying to remove it from my devices list. I appreciate any ideas. Which is correct “Is that yours?” or “Is that your’s?”?  I ask because it is possessive, so I would think it would be the latter, but I typically use and see the former usage.  Are there particular cases in which one should be used instead of the other? Or is one simply correct and the other not?  This is one of the few things that still confuse me, so help is greatly appreciated. apex:inputField can only be used with sObjects I am trying to create a custom visualforce page that saves new opportunity contact roles to an opportunity. I am having trouble creating the first step of listing out all contacts that relate to that account. The error I am getting is...     Save error: Could not resolve the entity from  value binding '{!u.contact}'.   can only be used with SObjects, or objects that are Visualforce field component resolvable.   I do not understand why I am receiving this error. u.contact should resolve to a Contact object, which is an sObject. Am I misunderstanding something?  Here is my code...  Controller  public class ChooseContactController  {     public String accountId = ApexPages.currentPage().getParameters().get('accountId');     public Account account { get; set; }     public List&lt;UnfundedOpportunityContactRole&gt; unfundedOpportunityContactRoles { get; set; }      public ChooseContactController()      {          unfundedOpportunityContactRoles = new List&lt;UnfundedOpportunityContactRole&gt;();         List&lt;Contact&gt; contacts = [SELECT Id, Name FROM Contact WHERE AccountId =: accountId];         account = [SELECT Id, Name FROM Account WHERE Id =: accountId];          for(Contact c: contacts)          {             unfundedOpportunityContactRoles.add(new UnfundedOpportunityContactRole(c, 'The Man'));         }     }      public void Save() {}     public void Create() {}      public class UnfundedOpportunityContactRole     {         public Contact contact { get; set; }         public String role { get; set; }          public UnfundedOpportunityContactRole() { }          public UnfundedOpportunityContactRole(Contact contactParam, String roleParam)         {             this.contact = contactParam;             this.role = roleParam;         }     } }   VF page  &lt;apex:page controller="ChooseContactController"&gt;   &lt;apex:form &gt;     &lt;apex:pageBlock title="Choose a contact" mode="edit"&gt;       &lt;apex:pageBlockButtons &gt;         &lt;apex:commandButton action="{!create}" value="New"/&gt;         &lt;apex:commandButton action="{!save}" value="Save"/&gt;       &lt;/apex:pageBlockButtons&gt;         &lt;apex:pageBlockSection title="{!account.Name}"&gt;           &lt;apex:dataTable value="{!unfundedOpportunityContactRoles}" var="u"&gt;             &lt;apex:column headerValue="Contact"&gt;               &lt;apex:inputField value="{!u.contact}" /&gt;             &lt;/apex:column&gt;             &lt;apex:column headerValue="Role"&gt;               &lt;apex:inputField value="{!u.role}" /&gt;             &lt;/apex:column&gt;           &lt;/apex:dataTable&gt;         &lt;/apex:pageBlockSection&gt;     &lt;/apex:pageBlock&gt;   &lt;/apex:form&gt; &lt;/apex:page&gt; Are there rules for falling in water vs. diving vs. just jumping in for various depths of water? Just realized that in DMing 5e I have unconsciously used a falling-in-water rule-of-thumb that I inherited from somewhere (maybe 2e or AD&amp;D or maybe even Pathfinder). The ruling I've been using is as follows:   No damage for 20 feet of falling. Half-damage next 20 feet. Normal damage beyond that.   Realizing there should be a Strength (Athletics) for "swimming" (in context, "diving") to take even less damage with a proper dive in sufficiently deep water, I started to look for specifics on that. Am I just missing it somewhere? (Also didn't find it searching this stack.)  Are there clear 5e rules for both jumping and diving in water of various depths? How to label using just numbers from start of text field? How do I save terminal output to a file? How do I save the output of a command to a file?  Is there a way without using any software? I would like to know how. How to deal with very long lines that do not contain spaces? How do I eliminate reflection on glass? When I take a picture through a window, I often see a reflection on the glass. I have noticed that this occurs mostly when it is dark or overcast outside or it is especially bright on my side of the glass. How can I stop this?