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  • Java: ListA.addAll(ListB) fires NullPointerException?

    - by HH
    The err part is Capitalized in the code, it also comes in foreaching. Because of the abstract list, it cannot be initialized, declaration is in a static field. The lists have the same type. import java.util.*; public class Test { public static final List<String> highPrio = Arrays.asList("*","/"); public static List<String> ops; public static void main(String[] args) { //ERROR HERE, why do it throw nullPointer? ops.addAll(highPrio); for(String s : ops) { System.out.println(s); } } }

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  • C++: Question about freeing memory

    - by Martijn Courteaux
    On Learn C++, they wrote this to free memory: int *pnValue = new int; // dynamically allocate an integer *pnValue = 7; // assign 7 to this integer delete pnValue; pnValue = 0; My question is: "Is the last statement needed to free the memory correctly, completly?" I thought that the pointer *pnValue was still on the stack and new doesn't make any sense to the pointer. And if it is on the stack it will be cleaned up when the application leaves the scope (where the pointer is declared in), isn't it?

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  • Express one dimension of 2d array as new array

    - by user208080
    I have a 2d array a[3,3]. How can I express one dimension as a new array and pass it to some function? int[,] a = new int[3,3]; a[0,0] = 1; ... string b = concatenate(a[0]); // where concatenate is a function // take a one dimension array as param Also, can I create a 65000x65000 array with C#? I got some "out of memory" error.

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  • new Integer vs valueOf

    - by LB
    Hi, I was using Sonar to make my code cleaner, and it pointed that I'm using new Integer(1) instead of Integer.valueOf(1). Because it seems that valueOf does not instantiate a new object so is more memory-friendly. How can valueOf not instantiate a new object ? How does it work ? Is this true for all integers ? thanks.

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  • How to iterate over function arguments

    - by Jack
    I have a Python function accepting several string arguments def foo(a, b, c): and concatenating them in a string. I want to iterate over all function arguments to check they are not None. How it can be done? Is there a quick way to convert None to ""? Thanks.

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  • Several modules in a package importing one common module

    - by morpheous
    I am writing a python package. I am using the concept of plugins - where each plugin is a specialization of a Worker class. Each plugin is written as a module (script?) and spawned in a separate process. Because of the base commonality between the plugins (e.g. all extend a base class 'Worker'), The plugin module generally looks like this: import commonfuncs def do_work(data): # do customised work for the plugin print 'child1 does work with %s' % data In C/C++, we have include guards, which prevent a header from being included more than once. Do I need something like that in Python, and if yes, how may I make sure that commonfuncs is not 'included' more than once?

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  • Stop overlooking minor details

    - by Mark Lubin
    Compared to most people on this site I am admittedly a novice. I wanted to get some advice from the pros on how to avoid making stupid errors in your code. Is there anyone else who had the problem when they were first starting out of missing some detail that causes big problems? Are there any habits or behaviors that helped you over come this.

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  • Normal C++ code in Qt doesnt build and run

    - by Nick
    Hello. I am using Qt under linux, if it matters. I ran successfully under Geany (a simple c++ compiler) the following: //my first program in C++ Hello World! include using namespace std; int main () {cout << "Hello World!"; return 0;} I opened Qt source file and copied the exact same code and i can't build or run. Thank you for your responses to this simple problem.

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  • C++ STL: Trouble with string iterators

    - by Rosarch
    I'm making a simple command line Hangman game. void Hangman::printStatus() { cout << "Lives remaining: " << livesRemaining << endl; cout << getFormattedAnswer() << endl; } string Hangman::getFormattedAnswer() { return getFormattedAnswerFrom(correctAnswer.begin(), correctAnswer.end()); } string Hangman::getFormattedAnswerFrom(string::const_iterator begin, string::const_iterator end) { return begin == end? "" : displayChar(*begin) + getFormattedAnswerFrom(++begin, end); } char Hangman::displayChar(const char c) { return c; } (Eventually, I'll change this so displayChar() displays a - or a character if the user has guessed it, but for simplicity now I'm just returning everything.) When I build and run this from VS 2010, I get a popup box: Debug Assertion Failed! xstring Line: 78 Expression: string iterator not dereferenceable What am I doing wrong?

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  • If you could remove one feature of php ti help newbies what would it be?

    - by Chris
    If you could remove one feature from PHP so as to discourage, prevent or otherwise help stop newer programmers develop bad habits or practices, or, to stop them falling into traps that might hinder their development skills what would it be and why? Now, before the votes to close it's not as open-ended as you might think. I'm not asking purely what is the worst feature or what feature would you really like to remove purely arbitrarily. Yes, there may not be one correct answer but I suspect there will be many similar answers which will provide me with a good idea of things I might be doing wrong, even inadvertently.

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  • What's a good starting point, tutorial, or project, to learn database programming?

    - by DarthNoodles
    I've been a Software Developer now for over 10 years. I've mostly worked in Embedded C with some time spent on C++ (limited) and Java. I'm looking to learn some new technologies and skills. I thought that database programming may be interesting to learn. I would like to make my own pet project in order to learn these things. My platform of choice is Windows but can work in Linux also. My ideal pet project would involve a GUI and some network/internet programming also which I have some experience doing. I wouldn't mind getting into C# but don't want to bite off more than I can chew right now as my spare time is limited. If I understand correctly SQLite allows for programs to use a database without running an ODBC server. Is this correct? Is that a good place to start? What can I do to start that is not too complicated but not so simple that I won't learn the details also? Your opinions and feedback would be appreciated.

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  • Differences between DB2 and Oracle

    - by Ondrej Slinták
    We had a talk with colleagues about databases yesterday as we will have a DB2 education in few weeks. I'm wondering, what are the differences between DB2 and Oracle as two major enterprise solutions? Are there any limitations in comparison to each other? Are there any tasks more suitable for DB2 or Oracle? (I found this article, but I somehow doubt it covers everything)

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  • How to execute an exe using Javascript?

    - by Karthick
    I need to open an EXE from a folder, when the folder is present, using javascript. I have added the code, but am not able to open the EXE after checking the folder, please share your thoughts. <html> <body> <script language="JScript"> <!-- function checkfolder() { var myObject; myObject = new ActiveXObject("Scripting.FileSystemObject"); if(myObject.FolderExists("\\tmp")) { alert("tmp Folder Exists"); } else { alert("tmp Folder doesn't exist"); } } --> </script> Check for folder "tmp" <form name="myForm"> <input type="Button" value="Check Folder" onClick='checkfolder()'> </form> </body> </html>

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  • Processor, OS : 32bit, 64 bit

    - by Sandbox
    I am new to programming and come from a non-CS background (no formal degree). I mostly program winforms using C#. I am confused about 32 bit and 64 bit.... I mean, have heard about 32 bit OS, 32 bit processor and based on which a program can have maximum memory. How it affects the speed of a program. There are lot more questions which keep coming to mind. I tried to go through some Computer Organization and Architecture books. But, either I am too dumb to understand what is written in there or the writers assume that the reader has some CS background. Can someone explain me these things in a plain simple English or point me to something which does that. EDIT: I have read things like In 32-bit mode, they can access up to 4GB memory; in 64-bit mode, they can access much much more....I want to know WHY to all such things. BOUNTY: Answers below are really good....esp one by Martin. But, I am looking at a thorough explanation, but in plain simple English.

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  • F# - Function with no arguments?

    - by Rubys
    When thinking in a functional mindset, given that functions are supposed to be pure, one can conclude any function with no arguments is basically just a value. However, reallity gets in the way, and with different inputs, I might not need a certain function, and if that function is computationally expensive, I'd like to not evaluate it if it's not needed. I found a workaround, using let func _ = ... and calling it with func 1 or whatever, but that feels very non-idiomatic and confusing to the reader. This boils down to one question: In F#, Is there a proper way to declare a function with zero arguments, without having it evaluated on declaration?

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  • linked list problem (with insert)

    - by JohnWong
    The problem appears with the insert function that I wrote. 3 conditions must work, I tested b/w 1 and 2, b/w 2 and 3 and as last element, they worked. But b/w 3 and 4, it did not work. It only display up to the new added record, and did not show the fourth element. Efficiency is not my concern here (not yet). Please guide me through this debug process. Thank you very much. #include<iostream> #include<string> using namespace std; struct List // we create a structure called List { string name; string tele; List *nextAddr; }; void populate(List *); void display(List *); void insert(List *); int main() { const int MAXINPUT = 3; char ans; List * data, * current, * point; // create two pointers data = new List; current = data; for (int i = 0; i < (MAXINPUT - 1); i++) { populate(current); current->nextAddr = new List; current = current->nextAddr; } // last record we want to do it sepeartely populate(current); current->nextAddr = NULL; cout << "The current list consists of the following data records: " << endl; display(data); // now ask whether user wants to insert new record or not cout << "Do you want to add a new record (Y/N)?"; cin >> ans; if (ans == 'Y' || ans == 'y') { /* To insert b/w first and second, use point as parameter between second and third uses point->nextAddr between third and fourth uses point->nextAddr->nextAddr and insert as last element, uses current instead */ point = data; insert(()); display(data); } return 0; } void populate(List *data) { cout << "Enter a name: "; cin >> data->name; cout << "Enter a phone number: "; cin >> data->tele; return; } void display(List *content) { while (content != NULL) { cout << content->name << " " << content->tele; content = content->nextAddr; cout << endl; // we skip to next line } return; } void insert(List *last) { List * temp = last->nextAddr; //save the next address to temp last->nextAddr = new List; // now modify the address pointed to new allocation last = last->nextAddr; populate(last); last->nextAddr = temp; // now link all three together, eg 1-NEW-2 return; }

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  • Relationship problem?

    - by dilip
    I have four tables Tag=id,tag_name Image=Id,Image_name TagImage=Id,tag_id,Image_id ImageStudent=id,Image_id,student_id And I want to find a record using student id and tag name. What relationship do I use?

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  • what is the regular expression for this

    - by bn
    I want to parse this (adv) much (thanks) I want to eliminate the words and the bracket (adv) but not (thanks) the condition is: inside bracket, and word length inside bracket is 1-5 characters I am using preg_match in PHP Thank You

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