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• Find valid assignments of integers in arrays (permutations with given order)

  - by evident

  Hi everybody! I am having a general problem finding a good algorithm for generating each possible assignment for some integers in different arrays. Lets say I have n arrays and m numbers (I can have more arrays than numbers, more numbers than arrays or as much arrays as numbers). As an example I have the numbers 1,2,3 and three arrays: { }, { }, { } Now I would like to find each of these solutions: {1,2,3}, { }, { } { }, {1,2,3}, { } { }, { }, {1,2,3} {1,2}, {3}, { } {1,2}, { }, {3} { }, {1,2}, {3} {1}, {2,3}, { } {1}, { }, {2,3} { }, {1}, {2,3} {1}, {2}, {3} So basically I would like to find each possible combination to assign the numbers to the different arrays with keeping the order. So as in the example the 1 always needs to come before the others and so on... I want to write an algorithm in C++/Qt to find all these valid combinations. Does anybody have an approach for me on how to handle this problem? How would I generate these permutations?

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• How to create static method that evaluates local static variable once?

  - by Viet

  I have a class with static method which has a local static variable. I want that variable to be computed/evaluated once (the 1st time I call the function) and for any subsequent invocation, it is not evaluated anymore. How to do that? Here's my class: template< typename T1 = int, unsigned N1 = 1, typename T2 = int, unsigned N2 = 0, typename T3 = int, unsigned N3 = 0, typename T4 = int, unsigned N4 = 0, typename T5 = int, unsigned N5 = 0, typename T6 = int, unsigned N6 = 0, typename T7 = int, unsigned N7 = 0, typename T8 = int, unsigned N8 = 0, typename T9 = int, unsigned N9 = 0, typename T10 = int, unsigned N10 = 0, typename T11 = int, unsigned N11 = 0, typename T12 = int, unsigned N12 = 0, typename T13 = int, unsigned N13 = 0, typename T14 = int, unsigned N14 = 0, typename T15 = int, unsigned N15 = 0, typename T16 = int, unsigned N16 = 0> struct GroupAlloc { static const uint32_t sizeClass; static uint32_t getSize() { static uint32_t totalSize = 0; totalSize += sizeof(T1)*N1; totalSize += sizeof(T2)*N2; totalSize += sizeof(T3)*N3; totalSize += sizeof(T4)*N4; totalSize += sizeof(T5)*N5; totalSize += sizeof(T6)*N6; totalSize += sizeof(T7)*N7; totalSize += sizeof(T8)*N8; totalSize += sizeof(T9)*N9; totalSize += sizeof(T10)*N10; totalSize += sizeof(T11)*N11; totalSize += sizeof(T12)*N12; totalSize += sizeof(T13)*N13; totalSize += sizeof(T14)*N14; totalSize += sizeof(T15)*N15; totalSize += sizeof(T16)*N16; totalSize = 8*((totalSize + 7)/8); return totalSize; } };

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• Static Variables in Overloaded Functions

  - by BSchlinker

  I have a function which does the following: When the function is called and passed a true bool value, it sets a static bool value to true When the function is called and passed a string, if the static bool value is set to true, it will do something with that string Here is my concern -- will a static variable remain the same between two overloaded functions? If not, I can simply create a separate function designed to keep track of the bool value, but I try to keep things simple.

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• Inherit static properties in subclass without redeclaration?

  - by David

  Hi, I'm having the same problem as this guy with the application I'm writing right now. The problem is that static properties are not being inherited in subclasses, and so if I use the static:: keyword in my main class, it sets the variable in my main class as well. It works if I redeclare the static variables in my subclass, but I expect to have a large number of static properties and subclasses and wish to avoid code duplication. The top-rated response on the page I linked has a link to a few "workarounds", but it seems to have 404'd. Can anyone lend me some help or perhaps point me in the direction of said workarounds?

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• non static method cannot be referenced from a static context.

  - by David

  First some code: import java.util.*; ... class TicTacToe { ... public static void main (String[]arg) { Random Random = new Random() ; toerunner () ; // this leads to a path of methods that eventualy gets us to the rest of the code } ... public void CompTurn (int type, boolean debug) { ... boolean done = true ; int a = 0 ; while (!done) { a = Random.nextInt(10) ; if (debug) { int i = 0 ; while (i<20) { System.out.print (a+", ") ; i++; }} if (possibles[a]==1) done = true ; } this.board[a] = 2 ; } ... } //to close the class Here is the error message: TicTacToe.java:85: non-static method nextInt(int) cannot be referenced from a static context a = Random.nextInt(10) ; ^ What exactly went wrong? What does that error message "non static method cannot be referenced from a static context" mean?

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• Why and when should I make a class 'static'? What is the purpose of 'static' keyword on classes?

  - by Saeed Neamati

  The static keyword on a member in many languages mean that you shouldn't create an instance of that class to be able to have access to that member. However, I don't see any justification to make an entire class static. Why and when should I make a class static? What benefits do I get from making a class static? I mean, after declaring a static class, one should still declare all members which he/she wants to have access to without instantiation, as static too. This means that for example, Math class could be declared normal (not static), without affecting how developers code. In other words, making a class static or normal is kind of transparent to developers.

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• Can't I just use all static methods?

  - by Reddy S R

  What's the difference between the two UpdateSubject methods below? I felt using static methods is better if you just want to operate on the entities. In which situations should I go with non-static methods? public class Subject { public int Id {get; set;} public string Name { get; set; } public static bool UpdateSubject(Subject subject) { //Do something and return result return true; } public bool UpdateSubject() { //Do something on 'this' and return result return true; } } I know I will be getting many kicks from the community for this really annoying question but I could not stop myself asking it. Does this become impractical when dealing with inheritance?

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• "continue" and "break" for static analysis

  - by B. VB.

  I know there have been a number of discussions of whether break and continue should be considered harmful generally (with the bottom line being - more or less - that it depends; in some cases they enhance clarity and readability, but in other cases they do not). Suppose a new project is starting development, with plans for nightly builds including a run through a static analyzer. Should it be part of the coding guidelines for the project to avoid (or strongly discourage) the use of continue and break, even if it can sacrifice a little readability and require excessive indentation? I'm most interested in how this applies to C code. Essentially, can the use of these control operators significantly complicate the static analysis of the code possibly resulting in additional false negatives, that would otherwise register a potential fault if break or continue were not used? (Of course a complete static analysis proving the correctness of an aribtrary program is an undecidable proposition, so please keep responses about any hands-on experience with this you have, and not on theoretical impossibilities) Thanks in advance!

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• "static" as a semantic clue about statelessness?

  - by leoger

  this might be a little philosophical but I hope someone can help me find a good way to think about this. I've recently undertaken a refactoring of a medium sized project in Java to go back and add unit tests. When I realized what a pain it was to mock singletons and statics, I finally "got" what I've been reading about them all this time. (I'm one of those people that needs to learn from experience. Oh well.) So, now that I'm using Spring to create the objects and wire them around, I'm getting rid of static keywords left and right. (If I could potentially want to mock it, it's not really static in the same sense that Math.abs() is, right?) The thing is, I had gotten into the habit of using static to denote that a method didn't rely on any object state. For example: //Before import com.thirdparty.ThirdPartyLibrary.Thingy; public class ThirdPartyLibraryWrapper { public static Thingy newThingy(InputType input) { new Thingy.Builder().withInput(input).alwaysFrobnicate().build(); } } //called as... ThirdPartyLibraryWrapper.newThingy(input); //After public class ThirdPartyFactory { public Thingy newThingy(InputType input) { new Thingy.Builder().withInput(input).alwaysFrobnicate().build(); } } //called as... thirdPartyFactoryInstance.newThingy(input); So, here's where it gets touchy-feely. I liked the old way because the capital letter told me that, just like Math.sin(x), ThirdPartyLibraryWrapper.newThingy(x) did the same thing the same way every time. There's no object state to change how the object does what I'm asking it to do. Here are some possible answers I'm considering. Nobody else feels this way so there's something wrong with me. Maybe I just haven't really internalized the OO way of doing things! Maybe I'm writing in Java but thinking in FORTRAN or somesuch. (Which would be impressive since I've never written FORTRAN.) Maybe I'm using staticness as a sort of proxy for immutability for the purposes of reasoning about code. That being said, what clues should I have in my code for someone coming along to maintain it to know what's stateful and what's not? Perhaps this should just come for free if I choose good object metaphors? e.g. thingyWrapper doesn't sound like it has state indepdent of the wrapped Thingy which may itself be mutable. Similarly, a thingyFactory sounds like it should be immutable but could have different strategies that are chosen among at creation. I hope I've been clear and thanks in advance for your advice!

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• Defend zero-based arrays

  - by DrJokepu

  A question asked here recently reminded me of a debate I had not long ago with a fellow programmer. Basically he argued that zero-based arrays should be replaced by one-based arrays since arrays being zero based is an implementation detail that originates from the way arrays and pointers and computer hardware work, but these sort of stuff should not be reflected in higher level languages. Now I am not really good at debating so I couldn't really offer any good reasons to stick with zero-based arrays other than they sort of feel like more appropriate. I am really interested in the opinions of other developers, so I sort of challenge you to come up with reasons to stick with zero-based arrays!

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• Cost effective way to provide static media content

  - by james

  I'd like to be able to deliver around 50MB of static content, either in about 30 individual files up to 10MB or grouped into 3 compressed files, around 5k to 20k times a day. Ideally I'd like to put some sort of very basic security around providing the data to ensure that a request is from the expected source, but if tossing the security for a big reduction in price is possible then it's an option. Does anyone have any suggestions other than what I've found: Google AppEngine is $0.12/GB & I believe has a file size limit of 10MB so I'd have to break the data up a bit. So a rough calculation would seem to be that this would cost me about $30 to $120 a day. Or I've seen something like what seems to be just public static content delivery with no type of logic capabilities like Usenet.nl at what I think calculates to about $0.025/GB which would cost me about $6 to $25 a day. Any idea if I'm going about these calculations right & if there might be a better option for just static content on a decently high volume delivery? Again some basic security would be great but if cost is greatly reduced without it then I'm up for that.

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• Static IP Address on Ubuntu 12.04 Virtual Machine

  - by chrisnankervis

  I've setup a VM running Ubuntu 12.04 specifically for local web development and am having some problems ensuring it has a static IP address. A static IP address is important as I'm using the IP address in my hosts file to assign a .local suffix to addresses used both in browser and to connect to the correct database on the VM. Currently, every time I connect to a new network or my VM is assigned a new IP address I need to reconfigure my whole environment which is becoming quite a pain. It also probably doesn't help that the default-lease-time on the Ubuntu VM is set to 1800 by default. At the moment I'm using VMWare Fusion and the Network Adapter is enabled and set to "Autodetect" under Bridged Networking. I've tried to set a static IP address within the dhcpd.conf using the code below: host ubuntu { hardware ethernet 00:50:56:35:0f:f1; fixed-address: 192.168.100.100; } The fixed-address that I've used is also outside the range specified in the subnet block (which in this case is 192.168.100.128 to 192.168.100.254). I've tried adding and removing the network adapter and restarting my Mac after each time to no avail. Below is an ifconfig of the VM that might be of some help: eth0 Link encap:Ethernet HWaddr 00:50:56:35:0f:f1 inet addr:192.168.0.25 Bcast:192.168.0.255 Mask:255.255.255.0 inet6 addr: fe80::250:56ff:fe35:ff1/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1624 errors:0 dropped:0 overruns:0 frame:0 TX packets:416 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:147348 (147.3 KB) TX bytes:41756 (41.7 KB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) Are there any specific issues with 12.04 that I'm missing? Otherwise has anyone else got any ideas? Thanks in advance.

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• Ubuntu 12.04 Network Manager: unable to save manual setting to set up a static ip

  - by Andy

  I am fairly familiar with setting up servers, and ubuntu is generally my flavor of choice, but I just installed 12.04 desktop and I am seeing some behavior in network manager that is really puzzling. The network connection works fine if I leave it set on dhcp, but I would like a static IP address for my new web server. When I go into network manager and edit the connection for the one and only NIC I can select MANUAL from the dropdown menu but as soon as I do the Save button becomes greyed out. Even after filling out all fields for the connection it is still grey and I am unable to save the static IP connection information. Any thoughts would be greatly appreciated. I'm hoping there is just some new setting that I am unaware of.... On another note, if I stop the network manager and go edit the interfaces file (and the appropriate hosts/routes/dns files), I do get a static ip address assigned and I can contact my server from the outside, however, the server cannot find the internet. Can't ping even its own ip... I can ping the loopback interface though. I'm really confused on this one. Hoping someone can offer some help.

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• Is a Java static block equivalent to a C3 static constructor?

  - by Mackenzie

  What is the real difference between a C# static constructor and a Java static block? They both must be parameterless. They are both called only once, when the related class is first used. Am I missing something, or are they the same thing, just with different names?

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• What can I do with dynamic typing that I can not do with static typing

  - by Justin984

  I've been using python for a few days now and I think I understand the difference between dynamic and static typing. What I don't understand is why it's useful. I keep hearing about its "flexibility" but it seems like it just moves a bunch of compile time checks to runtime, which means more unit tests. This seems like an awfully big tradeoff to make for small advantages like readability and "flexibility". Can someone provide me with a real world example where dynamic typing allows me to do something I can't do with static typing?

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• Using static in PHP

  - by nischayn22

  I have a few functions in PHP that read data from functions in a class readUsername(int userId){ $reader = getReader(); return $reader->getname(userId); } readUserAddress(){ $reader = getReader(); return $reader->getaddress(userId); } All these make a call to getReader() { require_once("Reader.php"); static $reader = new Reader(); return $reader; } An overview of Reader class Reader{ getname(int id) { //if in-memory cache exists for this id return that //else get from db and cache it } getaddress(int id) { $this->getname(int id); //get address from name here } /*Other stuff*/ } Why is class Reader needed The Reader class does some in-memory caching of user details. So, I need only one object of class Reader and it will cache the user details instead of making multiple db calls. I am using static so that it the object gets created only once. Is this the right approach or should I do something else?

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• Size of static libraries generated by XCode

  - by shaft80

  I have a project tree in XCode that looks like this: AppProject depends on ObjcWrapper that in turn depends on PureCppLib. ObjcWrapper and PureCppLib are static library projects. Combined, all sources barely reach 15k lines of code, and, as expected, the size of resulting binary is about 750Kb in release mode and slightly over 1Mb in debug mode. So far, so good. However, ObjcWraper.a and PureCppLib.a are over 6Mb each in either mode. So the first question is why it is so. But more importantly, how can I ensure that those static libs do not include parts or all of the source code? Thanks in advance!

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• When should I use static methods in a class and what are the benefits?

  - by NAVEED

  I have concept of static variables but what are the benefits of static methods in a class. I have worked on some projects but I did not make a method static. Whenever I need to call a method of a class, I create an object of that class and call the desired method. Static variable in a method holds it's value even when method is executed but accessible only in its containing method but what is the best definition of static method? Is calling the static method without creating object of that class is the only benefit of static method? What is the accessible range for static method? What is the syntax to create and calling static method in php? Thanks

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• Hide struct definition in static library.

  - by BobMcLaury

  Hi, I need to provide a C static library to the client and need to be able to make a struct definition unavailable. On top of that I need to be able to execute code before the main at library initialization using a global variable. Here's my code: private.h #ifndef PRIVATE_H #define PRIVATE_H typedef struct TEST test; #endif private.c (this should end up in a static library) #include "private.h" #include <stdio.h> struct TEST { TEST() { printf("Execute before main and have to be unavailable to the user.\n"); } int a; // Can be modified by the user int b; // Can be modified by the user int c; // Can be modified by the user } TEST; main.c test t; int main( void ) { t.a = 0; t.b = 0; t.c = 0; return 0; } Obviously this code doesn't work... but show what I need to do... Anybody knows how to make this work? I google quite a bit but can't find an answer, any help would be greatly appreciated. TIA!

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• resizing arrays when close to memory capacity

  - by user548928

  So I am implementing my own hashtable in java, since the built in hashtable has ridiculous memory overhead per entry. I'm making an open-addressed table with a variant of quadratic hashing, which is backed internally by two arrays, one for keys and one for values. I don't have the ability to resize though. The obvious way to do it is to create larger arrays and then hash all of the (key, value) pairs into the new arrays from the old ones. This falls apart though when my old arrays take up over 50% of my current memory, since I can't fit both the old and new arrays in memory at the same time. Is there any way to resize my hashtable in this situation Edit: the info I got for current hashtable memory overheads is from here How much memory does a Hashtable use? Also, for my current application, my values are ints, so rather than store references to Integers, I have an array of ints as my values.

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• Rebuilt website from static html to CMS need to redirect indexed links

  - by Michael Dunn

  I have rebuilt a website which was all created with static html pages, it has now been rebuilt using a CMS system. I need to find a way of redirecting all the existing links to there new corresponding pages which utilise friendly URL rewrites on the CMS based website I imagine there will be several hundred if not 1000s as i have pages and images linked from google. What is the most efficient way to complete this Thanks in advance Mike

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• Attaching a static library to an iphone/ipad application

  - by Jack

  Hello, which is the best approach to include a static library with into an application for iPhone or iPad? I could choose to compile the library supplying right platform and building a library file with the ar utility and then add as a framework to the project including the source of the library .c/.h and compile them together with the application The first approach seems simpler, because I won't care about managing all specific settings of the library I want to include but how can I create the library both for iPhone and iPad and allow xcode to use the right library upon linking? The second approach seems more complex since xcode will take care about compiling my application and the library (with different settings I suppose) then how should I go? I can easily add sources of the lib but I'll have to include the make scripts to allow xcode use them to build in the right way. Any suggestions about how to proceed? The library I'm trying to include is libssh. (I know that this library, of course, has already been compiled and tried succesfully on iPhone) Thanks in advance.

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• Static pages for large photo album

  - by Phil P

  I'm looking for advice on software for managing a largish photo album for a website. 2000+ pictures, one-time drop (probably). I normally use MarginalHack's album, which does what I want: pre-generate thumbnails and HTML for the pictures, so I can serve without needing a dynamic run-time, so there's less attack surface to worry about. However, it doesn't handle pagination or the like, so it's unwieldy for this case. This is a one-time drop for pictures from a wedding, with a shared usercode/password for distribution to the guests; I don't wish to put the pictures in a third-party hosting environment. I don't wish to use PHP, simply because that's another run-time to worry about, I might relent and use something dynamic if it's Python or Perl based (as I can maintain things written in those). I currently have: Apache serving static files, Album-generated, some sub-directories to divide up the content to be a little more manageable. Something like Album but with pagination already handled would be great, but I'm willing to have something a little more dynamic, if it lets people comment or caption and store the extra data in something like an sqlite DB. I'd want something light-weight, not a full-blown CMS with security updates every three months. I don't want to upload pictures of other peoples' children into a third-party free service where I don't know what the revenue model is. (For my site: revenue is none, costs out of pocket). Existing server hosting is *nix, Apache, some WSGI. Client-side I have MacOS. Any advice?

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• Defining a static array into a C or C++ source file.

  - by VansFannel

  Hello. I know this is a question that every programmer should know, but I do not know. Long time no C programming and I've forgotten a lot of things. My question is: I have three huge static arrays defined inside a header file. Someone told me that It's much better to declare them as extern in the header file, and define them in a single C or C++ source file. How can I do that? Here is my header file: #ifndef _TEMPLE_OBJECT_H_ #define _TEMPLE_OBJECT_H_ #define NUM_TEMPLE_OBJECT_VERTEX 10818 static const float TEMPLEVertices[NUM_TEMPLE_OBJECT_VERTEX * 3] = {...}; static const float TEMPLENormals[NUM_TEMPLE_OBJECT_VERTEX * 3] = {...}; static const float TEMPLETexCoords[NUM_TEMPLE_OBJECT_VERTEX * 3] = {...}; #endif If a use a C++ source file, may I need to define a class? Thank you.

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• Java Arrays.equals() returns false for two dimensional arrays.

  - by Achilles

  Hi there, I was just curious to know - why does Arrays.equals(double[][], double[][]) return false? when in fact the arrays have the same number of elements and each element is the same? For example I performed the following test. ` [java] double[][] a, b; int size =5; a=new double[size][size]; b=new double[size][size]; for( int i = 0; i < size; i++ ) for( int j = 0; j < size; j++ ){ a[i][j]=1.0; b[i][j]=1.0; } if(Arrays.equals(a, b)) System.out.println("Equal"); else System.out.println("Not-equal"); [/java] ` Returns false and prints "Not-equal. on the other hand, if I have something like this: [java] double[] a, b; int size =5; a=new double[size]; b=new double[size]; for( int i = 0; i < size; i++ ){ a[i]=1.0; b[i]=1.0; } if(Arrays.equals(a, b)) System.out.println("Equal"); else System.out.println("Not-equal"); } [/java] returns true and prints "Equal". Does the method only work with single dimensions? if so, is there something similar for multi-dimensional arrays in Java?

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