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• Set environment variable in Ubuntu

  - by Junho Park

  In Ubuntu, I'd like to switch my JAVA_HOME environment variable back and forth between Java 5 and 6. I open a terminal and type in the following to set the JAVA_HOME environment variable: export JAVA_HOME=/usr/lib/jvm/java-1.5.0-sun And in that same terminal window, I type the following to check that the environment variable has been updated: echo $JAVA_HOME And I see /usr/lib/jvm/java-1.5.0-sun which is what I'm expecting to see. In addition, I modify ~/.profile and set the JAVA_HOME environment variable to /usr/lib/jvm/java-1.5.0-sun. And now for the problem--when I open a new terminal window and I check my JAVA_HOME environment variable by typing in echo $JAVA_HOME I see that my JAVA_HOME environment variable has been reverted back to Java 6. When I reboot my machine (or log out and back in, I suppose) the JAVA_HOME environment variable is set to Java 5 (presumably because of the modification I made in my ~/.profile). Is there a way around this so that I can change my JAVA_HOME environment without having to log out and back in (AND make that environment variable change stick in all new terminal windows)?

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• call value inside a JS variable as a JS function name

  - by user1640668

  Hello I have a function to perform actions but name of the function is inside a variable... below code will get the URL's hashed part example: #JHON and remove # and store it inside URLHASH variable..example: JHON var urlhash = document.location.hash; urlhash = urlhash.replace(/^.*#/, ''); always there is a function name from that value inside variable and i want to call value inside that variable as a function name window.onload=function() { Value inside URLHASH variable should run as a name of a variable. example: jhon(); }; Is it possible ? I tried some codes but it calls variable name as a function not value inside the variable..help me..

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• How to improve variable overriding/overwriting in XSL?

  - by ChrisBenyamin

  I want to do the following: Declare a variable Go into a if-statement Overwrite the variable XSL says I can't declare a variable twice, so what can I do to improve this step? Another approach was to check if a variable is set at all. I did this, because i skipped the first step and declared the variable in the if-statement. In another if-statement I wanted to check if the variable exists at all.

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• Conflict between variable substitution and CJK characters in BASH

  - by AndreasT

  I encountered a problem with variable substitution in the BASH shell. Say you define a variable a. Then the command $> echo ${a//[0-4]/} prints its value with all the numbers ranged between 0 and 4 removed: $> a="Hello1265-3World" $> echo ${a//[0-4]/} Hello65-World This seems to work just fine, but let's take a look at the next example: $> b="?1265-3?" $> echo ${b//[0-4]/} ?1265-3? Substitution did not take place: I assume that is because b contains CJK characters. This issue extends to all cases in which square brackets are involved. Surprisingly enough, variable substitution without square brackets works fine in both cases: $> a="Hello1265-3World" $> echo ${a//2/} Hello165-3World $> b="?1265-3?" $> echo ${b//2/} ?165-3? Is it a bug or am I missing something? I use Lubuntu 12.04, terminal is lxterminal and echo $BASH_VERSION returns 4.2.24(1)-release. EDIT: Andrew Johnson in his comment stated that with gnome-terminal 4.2.37(1)-release the command works fine. I wonder whether it is a problem of lxterminal or of its specific 4.2.24(1)-release version.

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• Variable naming conventions?

  - by Ziv

  I've just started using ReSharper (for C#) and I kind of like its code smells finder, it shows me some things about my writing that I meant to fix a long time ago (mainly variable naming conventions). It caused me to reconsider some of my naming conventions for methods and instance variables. ReSharper suggests that instance variable be lower camel case and begin with an underscore. For a while I meant to make all my local variables lower camel case but is the underscore necessary? Do you find it comfortable? I don't like this convention but I also haven't tried it yet, what is you opinion of it? The second thing it prompted me to re-evaluate is my naming conventions for GUI event handlers. I usually use the VS standard of ControlName_Action and my controls usually use hungarian notation (as a suffix, to help clarify in code what is visible to the user and what isn't when dealing with similarly named variable) so I end up with OK_btn_Click(), what is your opinion of that? Should I succumb to the ReSharper convention or there are other equally valid options?

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• Need help with the naming convention for an incremental variable [closed]

  - by iStryker

  I am using a voting module, that allows you vote either up or down [or reset]. If you vote up, the value is +1. If you vote down, the value is -1. If you vote up then down, the value is -1. I want to extend this module to allow you to vote multiple times, and the votes to be incremental. Examples Up, Up = +1, +1 = +2 Up, Up, Down = +1, +1, -1 = +1 I want to create a new boolean variable. If FALSE/NULL then use the old system +1/-1. If TRUE, voting will be incremental. What should be the name of this variable be? I feel 'incremental' is not the correct name. This module is part of an open-source project and is used on 3,177+ websites, so I want to get the naming convention right. Naturally, I'll be setting an upper and lower limit the variable be. [ie 5 & 0] Side-question: Is there a mathematics term to describe something being either +1/-1?

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• Which are the fundamental stack manipulation operations?

  - by Aadit M Shah

  I'm creating a stack oriented virtual machine, and so I started learning Forth for a general understanding about how it would work. Then I shortlisted the essential stack manipulation operations I would need to implement in my virtual machine: drop ( a -- ) dup ( a -- a a ) swap ( a b -- b a ) rot ( a b c -- b c a ) I believe that the following four stack manipulation operations can be used to simulate any other stack manipulation operation. For example: nip ( a b -- b ) swap drop -rot ( a b c -- c a b ) rot rot tuck ( a b -- b a b ) dup -rot over ( a b -- a b a ) swap tuck That being said however I wanted to know whether I have listed all the fundamental stack manipulation operations necessary to manipulate the stack in any possible way. Are there any more fundamental stack manipulation operations I would need to implement, without which my virtual machine wouldn't be Turing complete?

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• Working with Temporal Data in SQL Server

  - by Dejan Sarka

  My third Pluralsight course, Working with Temporal Data in SQL Server, is published. I am really proud on the second part of the course, where I discuss optimization of temporal queries. This was a nearly impossible task for decades. First solutions appeared only lately. I present all together six solutions (and one more that is not a solution), and I invented four of them. http://pluralsight.com/training/Courses/TableOfContents/working-with-temporal-data-sql-server

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• Is there something special about the number 65535?

  - by Nick Rosencrantz

  2¹6-1 & 25 = 25 (or? obviously ?) A developer asked me today what is bitwise 65535 & 32 i.e. 2¹6-1 & 25 = ? I thought at first spontaneously 32 but it seemed to easy whereupon I thought for several minutes and then answered 32. 32 seems to have been the correct answer but how? 65535=2¹6-1=1111111111111111 (but it doesn't seem right since this binary number all ones should be -1(?)), 32 = 100000 but I could not convert that in my head whereupon I anyway answered 32 since I had to answer something. Is the answer 32 in fact trivial? Is in the same way 2¹6-1 & 25-1 =31? Why did the developer ask me about exactly 65535? Binary what I was asked to evaluate was 1111111111111111 & 100000 but I don't understand why 1111111111111111 is not -1. Shouldn't it be -1? Is 65535 a number that gives overflow and how do I know that?

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• What kind of specific projects can I do to master bitwise operations in C++? Also is there a canonical book? [closed]

  - by Ford

  I don't use C++ or bitwise operations at my current job but I'm thinking of applying to companies where it is a requirement to be fluent with them (on their tests anyway). So my question is: Can anyone suggest a project which will require gaining a fluency in bitwise operations to complete? On a side note, is there a canonical book on optimization techniques using bitwise operations since that seems to be an important use of them?

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• Python lower_case_with_underscores style convention: underscores not popular?

  - by squirrel

  PEP8 recommends using lowercase, with words separated by underscores as necessary to improve readability for variable and function names. I've seen this interpreted as lower_case_with_underscores by most people, although in practice and in Python's native methods it seems like lowercasewithoutunderscores is more popular. It seems like following PEP8 strictly would be awkward since it seems to suggest mixing both lower_case_with_underscores and lowercasewithoutunderscores, which would be inconsistent. What is your interpretation of PEP8's variable names, and what do you actually use in practice? (Personally, I like lowerCamelCase as a compromise between readability and ease of typing.)

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• Is Operator Overloading supported in C

  - by caramel23

  Today when I was reading about LCC(windows) compiler I find out it has the implemention for operator overloading . I'm puzzled because after a bit of googling , it has been confirm that operator overloading ain't support in standard C , but I read some people's comment mentioning LCC is ANSI-compliant . So my real question is , is LCC really standard C or it's just like objective-c , a C variant with object-oriented feature ?

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• Concept of bit fields

  - by user1369975

  Whenever I read a code like this: struct node { int x : 2; int p : 4; }n; with bit fields involved, I get really confused, as to how they are represented in memory, what is sizeof(n) etc., how does it differ with normal members of structures? I tried referring K&R and http://en.wikipedia.org/wiki/Bit_field but they little to remove my confusion. What concepts of bit fields am I failing to grasp?

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• PHP application variable... maybe?

  - by James

  I went to a PHP job interview, I was asked to implement a piece of code to detect visitors are bots to crawl thru the website and steal content. So I implemented a few lines of code to detect if the site is being refreshed/visited too quickly/often by using a session variable to store last visit timestamp. I got told that session varaibles can be manupilated by cookies etc, so I am wondering if there is a application variable that I can use to store the timestamp information against visitor IPs eg $_SERVER[REMOTE_ADDR]? I know that I can write the data to a file but it's not very good for a high traffic website. Regards James

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• Have loaded a php variable into flash but cant apply it in a function...

  - by Paul Elliot

  hi I have created an actionscript function which stops an animation on a specific frame which works fine. I have then loaded in a php file with a variable which will contain the number for the frame i want the animation to stop on. This has loaded in fine and i have loaded it in a function. what i cant seem to do is to get the variable into the function which tells the animation to stop playing. here is my code: //load variables varReceiver = new LoadVars(); // create an object to store the variables varReceiver.load("http://playground.nsdesign6.net/percentage/external.php"); //load variables //function1 varReceiver.onLoad = function() { //value is the var that is created. var paul = this.percentage; } //function1 //function2 this.onEnterFrame = function() { if(this._currentframe==(percentage)) { this.stop(); this.onEnterFrame = undefined; } } play(); //function2 cheers paul

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• In C++, what is the "order of precedence" for shadowed variable names?

  - by Emile Cormier

  In C++, what is the "order of precedence" for shadowed variable names? I can't seem to find a concise answer online. For example: #include <iostream> int shadowed = 1; struct Foo { Foo() : shadowed(2) {} void bar(int shadowed = 3) { std::cout << shadowed << std::endl; // What does this output? } int shadowed; }; int main() { Foo().bar(); } I can't think of any other scopes where a variable might conflict. Please let me know if I missed one.

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• default value of a variable at the time of declaration in C# and VB ??

  - by Khan

  Can anybody tell me what is the default value of a variable at the time of declaration in C# and vb??

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• Is it a good idea to define a variable in a local block for a case of a switch statement?

  - by Paperflyer

  I have a rather long switch-case statement. Some of the cases are really short and trivial. A few are longer and need some variables that are never used anywhere else, like this: switch (action) { case kSimpleAction: // Do something simple break; case kComplexAction: { int specialVariable = 5; // Do something complex with specialVariable } break; } The alternative would be to declare that variable before going into the switch like this: int specialVariable = 5; switch (action) { case kSimpleAction: // Do something simple break; case kComplexAction: // Do something complex with specialVariable break; } This can get rather confusing since it is not clear to which case the variable belongs and it uses some unnecessary memory. However, I have never seen this usage anywhere else. Do you think it is a good idea to declare variables locally in a block for a single case?

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• Is it bad practice to initialize a variable to a dummy value?

  - by froadie

  This question is a result of the answers to this question that I just asked. It was claimed that this code is "ugly" because it initializes a variable to a value that will never be read: String tempName = null; try{ tempName = buildFileName(); } catch(Exception e){ ... System.exit(1); } FILE_NAME = tempName; Is this indeed bad practice? Should one avoid initializing variables to dummy values that will never actually be used? (EDIT - And what about initializing a String variable to "" before a loop that will concatenate values to the String...? Or is this in a separate category? e.g. String whatever = ""; for(String str : someCollection){ whatever += str; } )

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• Suggested GA operators for a TSP problem?

  - by Mark

  I'm building a genetic algorithm to tackle the traveling salesman problem. Unfortunately, I hit peaks that can sustain for over a thousand generations before mutating out of them and getting better results. What crossover and mutation operators generally do well in this case?

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• How to make ARGB transparency using bitwise operators.

  - by Smejda

  I need to make transparency, having 2 pixels: pixel1: {A, R, G, B} - foreground pixel pixel2: {A, R, G, B} - background pixel A,R,G,B are Byte values each color is represented by byte value now I'm calculating transparency as: newR = pixel2_R * alpha / 255 + pixel1_R * (255 - alpha) / 255 newG = pixel2_G * alpha / 255 + pixel1_G * (255 - alpha) / 255 newB = pixel2_B * alpha / 255 + pixel1_B * (255 - alpha) / 255 but it is too slow I need to do it with bitwise operators (AND,OR,XOR, NEGATION, BIT MOVE)

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• Containers of reference_wrappers (comparison operators required?)

  - by kloffy

  If you use stl containers together with reference_wrappers of POD types, the following code works just fine: int i = 3; std::vector< boost::reference_wrapper<int> > is; is.push_back(boost::ref(i)); std::cout << (std::find(is.begin(),is.end(),i)!=is.end()) << std::endl; However, if you use non-POD types such as (contrived example): struct Integer { int value; bool operator==(const Integer& rhs) const { return value==rhs.value; } bool operator!=(const Integer& rhs) const { return !(*this == rhs); } }; It doesn't suffice to declare those comparison operators, instead you have to declare: bool operator==(const boost::reference_wrapper<Integer>& lhs, const Integer& rhs) { return boost::unwrap_ref(lhs)==rhs; } And possibly also: bool operator==(const Integer& lhs, const boost::reference_wrapper<Integer>& rhs) { return lhs==boost::unwrap_ref(rhs); } In order to get the equivalent code to work: Integer j = { 0 }; std::vector< boost::reference_wrapper<Integer> > js; js.push_back(boost::ref(j)); std::cout << (std::find(js.begin(),js.end(),j)!=js.end()) << std::endl; Now, I'm wondering if this is really the way it's meant to be done, since it seems impractical. It just seems there should be a simpler solution, e.g. templates: template<class T> bool operator==(const boost::reference_wrapper<T>& lhs, const T& rhs) { return boost::unwrap_ref(lhs)==rhs; } template<class T> bool operator==(const T& lhs, const boost::reference_wrapper<T>& rhs) { return lhs==boost::unwrap_ref(rhs); } There's probably a good reason why reference_wrapper behaves the way it does (possibly to accomodate non-POD types without comparison operators?). Maybe there already is an elegant solution and I just haven't found it.

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• PL/SQL Logical Operators evaluate whole function

  - by Chris

  I know in C like languages logical operators are evaluated one at a time so: false && really_expensive_function() is doesn't result in the function being called (I can't remember the CS name for this). Does the same happen in PL/SQL or do I need to break the IF parts out to separate blocks?

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• How to pass operators as parameters

  - by Rodion Ingles

  I have to load an array of doubles from a file, multiply each element by a value in a table (different values for different elements), do some work on it, invert the multiplication (that is, divide) and then save the data back to file. Currently I implement the multiplication and division process in two separate methods. Now there is some extra work behind the scenes but apart from the specific statements where the multiplication/division occurs, the rest of the code is identical. As you can imagine, with this approach you have to be very careful making any changes. The surrounding code is not trivial, so its either a case of manually editing each method or copying changes from one method to the other and remembering to change the * and / operators. After too many close calls I am fed up of this and would like to make a common function which implements the common logic and two wrapper functions which pass which operator to use as a parameter. My initial approach was to use function pointers: MultiplyData(double data) { TransformData(data, &(operator *)); } DivideData(double data) { TransformData(data, &(operator /)); } TransformData(double data, double (*func)(double op1, double op2)) { /* Do stuff here... */ } However, I can't pass the operators as pointers (is this because it is an operator on a native type?), so I tried to use function objects. Initially I thought that multiplies and divides functors in <functional> would be ideal: MultiplyData(double data) { std::multiplies<double> multFunct; TransformData(data, &multFunct); } DivideData(double data) { std::divides<double> divFunct; TransformData(data, &divFunct); } TransformData(double data, std::binary_function<double, double, double> *funct) { /* Do stuff here... */ } As you can see I was trying to use a base class pointer to pass the functor polymorphically. The problem is that std::binary_function does not declare an operator() member for the child classes to implement. Is there something I am missing, or is the solution to implement my own functor heirarchy (which really seems more trouble than it is worth)?

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• C/C++ Pre vs Post decrement and increment operators performance difference

  - by TimK

  In some of my programs I have noticed that in some cases there is a difference in speed when using either the pre(++i or --i) and post(i++ or i--) decrement operators. Sometimes pre is faster and other times post is faster. I can't seem to figure out why. Could someone please explain this to me?

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