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• c# copy constructor generator

  - by Shawn Mclean

  I want to copy values from one object to another object. Something similiar to pass by value but with assignment. Eg. PushPin newValPushPin = oldPushPin; //I want to break the reference here. I was told to write a copy constructor for this. But this class has alot of properties, it will probably take an hour to write a copy constructor by hand. Is there a better way to assign an object to another object by value? If not, is there a copy constructor generator?

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• Static string variable in Objective C on iphone

  - by Prajakta

  Hi, How to create & access static string in iPhone (objective c)? I declare static NSString *str = @"OldValue" in class A. If i assign some value to this in class B as str = @"NewValue". This value persists for all methods in class B. But if I access it in class C (after assignment in B) I am getting it as OldValue. Am I missing something? Should i use extern in other classes? Thanks & Regards, Yogini

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• Where is the mistake ?

  - by mr.bio

  Hi ... i am implementing a simple linked list in c++. I have a mistake and i don't see it :( #include <stdexcept> #include <iostream> struct Node { Node(Node *next, int value): next(next), value(value) { } Node *next; int value; }; class List { Node *first; // Erstes Element , 0 falls die Liste leer ist int len; // Laenge der liste Node *nthNode(int index); // Hilfsfunktion : O( index ) public: // Default - Konstruktor ( Laenge 0): O (1) List():first(0),len(0){ } // Copy - Konstruktor : O(other.len) List(const List & other){ }; // Zuweisungs - Operator O(len +other.len) List &operator=(const List &other) { clear(); if(!other.len) return *this; Node *it = first = new Node(0,other.first->value); for (Node *n = other.first->next; n; n = n->next) { it = it->next = new Node(0, n->value); } len = other.len; return *this; } // Destruktor ( gibt den Speicher von allen Nodes frei ): O( len ) ~List(){ }; // Haengt der Liste ein Element hinten an: O( len ) void push_back(int value){ }; // Fuegt am Anfang der Liste ein Element ein : O (1) void push_front(int value){ Node* front = new Node(0,value); if(first){ first = front; front->next = 0; }else{ front->next = first; first = front; } len++; }; // gibt eine Referenz auf das index -te Element zurueck : O( index ) int &at(int index){ int count = 0 ; int ret ; Node *it = first; for (Node *n = first->next; n; n = n->next) { if(count==index) ret = n->value; count++; } return ret ; }; // Entfernt alle Elemente : O(len) void clear(){ }; // Zeigt alle Elemente an: hier : O( len * len ) void show() { std::cout << " List [" << len << " ]:{ "; for (int i = 0; i < len; ++i) { std::cout << at(i) << (i == len - 1 ? '}' : ','); } std::cout << std::endl; } }; /* * */ int main() { List l; // l. push_back(1); // l. push_back(2); l. push_front(7); l. push_front(8); l. push_front(9); l.show(); // List(l). show(); } it works ... but the output is : List [3 ]:{ 0,134520896,9484585}

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• Dereferencing pointers without pointing them at a variable

  - by Miguel

  I'm having trouble understanding how some pointers work. I always thought that when you created a pointer variable (p), you couldn't deference and assign (*p = value) unless you either malloc'd space for it (p = malloc(x)), or set it to the address of another variable (p = &a) However in this code, the first assignment works consistently, while the last one causes a segfault: typedef struct { int value; } test_struct; int main(void) { //This works int* colin; *colin = 5; //This never works test_struct* carter; carter->value = 5; } Why does the first one work when colin isn't pointing at any spare memory? And why does the 2nd never work? I'm writing this in C, but people with C++ knowledge should be able to answer this as well.

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• Python nested function scopes

  - by Thomas O

  I have code like this: def write_postcodes(self): """Write postcodes database. Write data to file pointer. Data is ordered. Initially index pages are written, grouping postcodes by the first three characters, allowing for faster searching.""" status("POSTCODE", "Preparing to sort...", 0, 1) # This function returns the key of x whilst updating the displayed # status of the sort. ctr = 0 def keyfunc(x): ctr += 1 status("POSTCODE", "Sorting postcodes", ctr, len(self.postcodes)) return x sort_res = self.postcodes[:] sort_res.sort(key=keyfunc) But ctr responds with a NameError: Traceback (most recent call last): File "PostcodeWriter.py", line 53, in <module> w.write_postcodes() File "PostcodeWriter.py", line 47, in write_postcodes sort_res.sort(key=keyfunc) File "PostcodeWriter.py", line 43, in keyfunc ctr += 1 UnboundLocalError: local variable 'ctr' referenced before assignment How can I fix this? I thought nester scopes would have allowed me to do this. I've tried with 'global', but it still doesn't work.

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• Is this an example of polymorphism?

  - by computer-science-student

  I'm working on a homework assignment (a project), for which one criterion is that I must make use of polymorphism in a way which noticeably improves the overall quality or functionality of my code. I made a Hash Table which looks like this: public class HashTable<E extends Hashable>{ ... } where Hashable is an interface I made that has a hash() function. I know that using generics this way improves the quality of my code, since now HashTable can work with pretty much any type I want (instead of just ints or Strings for example). But I'm not sure if it demonstrates polymorphism. I think it does, because E can be any type that implements Hashable. In other words HashTable is a class which can work with (practically) any type. But I'm not quite sure - is that polymorphism? Perhaps can I get some clarification as to what exactly polymorphism is? Thanks in advance!

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• static arrays defined with unspecified size, empty brackets?

  - by ahmadabdolkader

  For the C++ code fragment below: class Foo { int a[]; // no error }; int a[]; // error: storage size of 'a' isn't known void bar() { int a[]; // error: storage size of 'a' isn't known } why isn't the member variable causing an error too? and what is the meaning of this member variable? I'm using gcc version 3.4.5 (mingw-vista special) through CodeBlocks 8.02. On Visual Studio Express 2008 - Microsoft(R) C/C++ Optimizing Compiler 15.00.30729.01 for 80x86, I got the following messages: class Foo { int a[]; // warning C4200: nonstandard extension used : zero-sized array in struct/union - Cannot generate copy-ctor or copy-assignment operator when UDT contains a zero-sized array }; int a[]; void bar() { int a[]; // error C2133: 'a' : unknown size } Now, this needs some explaination too.

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• What does the symbol :=: mean

  - by Dan Maguire

  I've found the symbol :=: in some Clarion code and I can't seem to figure out exactly what it does. The code was written by a previous developer many years ago, so I can't ask him. I also have not been able to find any results for "colon equals colon" in Google. Here is an example of the code, where bufSlcdpaDtl is a file object: lCCRecord Like(bufSlcdpaDtl),Pre(lCCRecord) ! ...other stuff... lCCRecord :=: bufSlcdpaDtl I'm wondering if it's something similar to ::= in Python or possibly the assignment operator :=.

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• Conversion of pointer-to-pointer between derived and base classes?

  - by Mike Mueller

  Regarding the following C++ program: class Base { }; class Child : public Base { }; int main() { // Normal: using child as base is allowed Child *c = new Child(); Base *b = c; // Double pointers: apparently can't use Child** as Base** Child **cc = &c; Base **bb = cc; return 0; } GCC produces the following error on the last assignment statement: error: invalid conversion from ‘Child**’ to ‘Base**’ My question is in two parts: Why is there no implicit conversion from Child** to Base**? I can make this example work with a C-style cast or a reinterpret_cast. Using these casts means throwing away all type safety. Is there anything I can add to the class definitions to make these pointers cast implicitly, or at least phrase the conversion in a way that allows me to use static_cast instead?

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• VS C++ throwing divide by zero exception after a specific check

  - by Dr. Monkey

  In the following C++ code, it should be impossible for ain integer division by zero to occur: // gradedUnits and totalGrades are both of type int if (gradedUnits == 0) { return 0; } else { return totalGrades/gradedUnits; //call stack points to this line } however Visual Studio is popping up this error: Unhandled exception at 0x001712c0 in DSA_asgn1.exe: 0xC0000094: Integer division by zero. And the stack trace points to the line indicated in the code. It seems like VS might just do this with any integer division, without checking whether a divide by zero is possible. Do I need to catch this exception even though the code should never be able to throw it? If so, what's the best way to go about this? This is for an assignment that specifies VS 2005/2008 with C++. I would prefer not to make things more complicated than I need to, but at the same time I like to do things properly where possible.

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• Why aren't these shared_ptrs pointing to the same container?

  - by BeeBand

  I have a class Model: class Model { ... boost::shared_ptr<Deck> _deck; boost::shared_ptr<CardStack> _stack[22]; }; Deck inherits from CardStack. I tried to make _stack[0] point to the same thing that _deck points to by going: { _deck = boost::shared_ptr<Deck>(new Deck()); _stack[0] = _deck; } It seems that the assignment to _deck of _stack[0] results in a copy of _deck being made. How can I get them to point to the same thing?

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• Riddle: Spot the serious bug in this bubble sort implementation

  - by ripper234

  (No, this isn't a homework assignment, I just found the bug and thought it might be useful to share it here) import java.util.List; public class BubbleSorter { public <T extends Comparable<T>> void sort(List<T> list) { while (true) { boolean didWork = false; for (int i = 0; i < list.size() - 1; ++i) { if (list.get(i).compareTo(list.get(i + 1)) > 0) { swap(list, i, i + 1); didWork = true; break; } } if (!didWork) return; } } private static <T> void swap(List<T> list, int i, int j) { T tmp = list.get(i); list.set(i, list.get(j)); list.set(j, tmp); } }

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• [Java] - Problem having my main thread sleeping

  - by Chris

  I'm in a Java class and our assignment is to let us explore threads in Java. So far so good except for this one this one problem. And I believe that could be because of my lack of understanding how Java threads work at the moment. I have the main thread of execution which spawns new threads. In the main thread of execution in main() I am calling Thread.sleep(). When I do I get an Unhandled exception type InterruptedException. I am unsure of why I am getting this? I thought this was because I needed a reference to the main thread so I went ahead and made a reference to it via Thread.currentThread(). Is this not the way to have the thread sleep? What I need to do is have the main thread wait/sleep/delay till it does it required work again. Any help would be much appreciated.

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• C++ Static array vs. Dynamic array?

  - by user69514

  What is the difference between a static array and a dynamic array in C++? I have to do an assignment for my class and it says not to use static arrays, only dynamic arrays. I've looked in the book and online, but I don't seem to understand. I thought static was created at compile time and dynamic at runtime, but I might be mistaken this with memory allocation. Can you explain to me the difference between static array and dynamic array in C++? Thnaks.

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• How to Access a Private Variable?

  - by SoulBeaver

  This question isn't meant to sound as blatantly insulting as it probably is right now. This is a homework assignment, and the spec sheet is scarce and poorly designed to say the least. We have a function: double refuel( int liter, GasStation *gs ) { // TODO: Access private variable MaxFuel of gs and decrement. } Sound simple enough? It should be, but the class GasStation comes with no function that accesses the private variable MaxFuel. So how can I access it anyway using the function refuel? I'm not considering creating a function setFuel( int liter ) because the teacher always complains rather energetically if I change his specification. So... I guess I have to do some sort of hack around it, but I'm not sure how to go about this without explicitely changing the only function in GasStation and giving it a parameter so that I can call it here. Any hints perhaps?

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• compiling cocos3d 0.7.2 with Xcode5 error

  - by jimmy

  I tried to compile my cocos3d 0.7.2 project with xcode5. I am already stuck at the first error I get with the line “super.parent = aNode;” in CC3ParametricMeshNodes.m. this line is in the setParent function: -(void) setParent: (CC3Node*) aNode { super.parent = aNode; [self deriveNameFrom: aNode]; if ( !mesh ) self.box = self.parentBoundingBox; } and the error I get is: CC3ParametricMeshNodes.m:246:15: Assignment to readonly property I am sure that there will be other errors after this one is fixed. Is there any topic on common errors that occur while compiling cocos3d 0.7.2 with Xcode5? Thanks

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• How to change the value of None in Python?

  - by michael

  I'm currently reading chapter 5.8 of Dive Into Python and Mark Pilgrim says: There are no constants in Python. Everything can be changed if you try hard enough. This fits with one of the core principles of Python: bad behavior should be discouraged but not banned. If you really want to change the value of None, you can do it, but don't come running to me when your code is impossible to debug. I tried this in the interpreter None = "bad" I get a SyntaxError: assignment to None Just out of curiosity how do you change None?

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• Question regarding built-in type variable is returned from a function

  - by Chan

  Hello, If a local object is returned in a function call, it has to do at least three steps: 1. Copy constructor is called to hold a copy. 2. Destroy local object. 3. A copy is return. For example: x = y + z If x is an integer object. A copy of y + z should be returned, then a new object is created, then assignment operator of x will take this object as parameter. So my question is: Is the same process used for built-in type such as int, double...? If they're not the same, how's it done? Thanks, Chan

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• Why is Read-Modify-Write necessary for registers on embedded systems?

  - by Adam Shiemke

  I was reading http://embeddedgurus.com/embedded-bridge/2010/03/different-bit-types-in-different-registers/, which said: With read/write bits, firmware sets and clears bits when needed. It typically first reads the register, modifies the desired bit, then writes the modified value back out and I have run into that consrtuct while maintaining some production code coded by old salt embedded guys here. I don't understand why this is necessary. When I want to set/clear a bit, I always just or/nand with a bitmask. To my mind, this solves any threadsafe problems, since I assume setting (either by assignment or oring with a mask) a register only takes one cycle. On the other hand, if you first read the register, then modify, then write, an interrupt happening between the read and write may result in writing an old value to the register. So why read-modify-write? Is it still necessary?

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• How do I check the validity of the Canadian Social Insurance Number in C#?

  - by user518307

  I've been given the assignment to write an algorithm in C# that checks the validity of a Canadian Social Insurance Number (SIN). Here are the steps to validate a SIN. Given an example Number: 123 456 782 Remove the check digit (the last digit): 123456782 Extract the even digits (2,4,6,8th digith): 12345678 Double them: 2 4 6 8 | | | | v v v v 4 8 12 16 Add the digits together: 4+8+1+2+1+6 = 22 Add the Odd placed digits: 1+3+5+7 = 16 Total : 38 Validity Algorithm If the total is a multiple of 10, the check digit should be zero. Otherwise, Subtract the Total from the next highest multiple of 10 (40 in this case) The check digit for this SIN must be equal to the difference of the number and the totals from earlier (in this case, 40-38 = 2; check digit is 2, so the number is valid) I'm lost on how to actually implement this in C#, how do I do this?

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• Array value setting in javascript

  - by Dennis

  Hello. Again I'm still new to this javascript thing, so just would like to know if there is another way of setting the values of an array (just like declaring it); //correct way of declaring an array and reusing var adata = new Array('1','2','3'); //reusing of variable adata[0] = '4'; adata[1] = '5'; adata[2] = '6' ** This part is my question; I want to declare the values of the array just like declaring them to minimize the number of lines; //array declaration var data = new Array('1','2','3'); //reusing of variable data = ['4','5','6']; --- (as an example) I get an error msg "Invalid assignment left-hand side" is this possible? If so, what is the correct syntax? I hope I'm making sense. Thanking you in advance.

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• Comparing COUNT values within a query?

  - by outsyncof

  I have the following tables in a relation: person(ssn,sex) employment(ssn,workweeksperyear) assume ssn is a key. My assignment was to do this: Given as input the number of weeks per year a person has worked, determine whether there are more males than females who work more weeks than the input value. SELECT COUNT(sex) AS NumMales FROM person WHERE sex = 'Male' AND ssn IN (SELECT ssn FROM employment WHERE workweeksperyear > 48); The above query gets me the number of males for an input value and I could do the same for number of females but how do I compare the 2 results? Any help will be greatly appreciated!

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• type of an array

  - by Tim

  Hi, when I need to pass an array to a function, it seems all the following declarations of the function will work void f(int arr[]) void f(int arr[4]) // is this one correct? for this: int a[]={1,2,3,4}; f(a); But when I assign an array to another array, it fails int a[]={1,2,3,4}; int b[4] = a; // error: array must be initialized with a brace-enclosed initializer So why an array passed as an argument of a function is okay, but used on the rhs of simple assignment is wrong? Thanks!

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• Is there a redmine plugin to create multiple issues at once?

  - by Jerph

  Redmine has a nice batch edit feature, but nothing equivalent for "batch create" (please correct me if I'm wrong!) FogBugz lets you quickly create multiple tickets with the same properties (type, status, assignment, etc.) via a ajax-ified text box at the bottom of any filtered view of tickets. Tickets created this way match the values of the filter (and the filter grouping value - there's a text-box at the bottom of each group). Toodledo has simpler option: it's "Add multiple tasks" feature is a textarea where each line is turned into an item. Is there a redmine plugin out there that adds functionality like either of the above?

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• How do you assign a variable with the result of a if..else block?

  - by Pierre Olivier Martel

  I had an argument with a colleague about the best way to assign a variable in an if..else block. His orignal code was : @products = if params[:category] Category.find(params[:category]).products else Product.all end I rewrote it this way : if params[:category] @products = Category.find(params[:category]).products else @products = Product.all end This could also be rewritten with a one-liner using a ternery operator (? :) but let's pretend that product assignment was longer than a 100 character and couldn't fit in one line. Which of the two is clearer to you? The first solution takes a little less space but I thought that declaring a variable and assigning it three lines after can be more error prone. I also like to see my if and else aligned, makes it easier for my brain to parse it!

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