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  • Understanding exceptional cases

    - by Justin
    I've been studying the use of exceptions in various php projects (such as Doctrine and Zend Framework). Exceptions seem to be thrown when unordinary input/state occurs. A perfect example is Doctrine throwing an exception when you try to use a invalid query string. I think the creators of the doctrine api understood that first, you can't query data by using an invalid DQL statement, and a developer should immediately be warned that an error has occurred, rather then letting execution continue with the possibility of an error code going un-checked. I also bet that this simplifies reading the code. I can't think of a situation where you would want to use an invalid DQL statement, except unit testing. Since this is true, it's better to avoid plaguing a bunch of code with null/error checks and use exceptions. I've read in books that exceptions shouldn't be thrown when validating dating user input. I've seen examples where of where the guideline is broken. One example is the Zend framework. If supplying an invalid controller or action name, an exception is thrown. Unlike doctrine, the user has more direct control over this sort of input. I know you can configure an error controller and set up a 404 message or what have you, but I'm curious why they have used an exception in this scenario? I guess you can argue the Zend Framework does not know how to continue processing the quest. One last example Is I wrote a function to return some html based on a given resource type. This resource type is hard-coded and sent when a user interacts with a web site (such as clicking a button to display the form to input data). I don't expect users to be mucking around with the request type. Under normal operating conditions, the resource type should be valid. To clean up some logic, I was going to throw an exception if a particular form wasn't found. This is mainly to find the correct form associated with a resource type so proper validation can occur. Does this sound like a valid use case for an exception? Right now it's pretty trivial, but I do plan to implement a restful consumer and re-using a function to map resources to their validation services would be very useful. I can then catch the exception and based on the consumer, return an error message suitable for the request type...

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  • Apache authentication, security exceptions and safari

    - by Purcell
    I have apache authentication set up on a site, it works fine in firefox and chrome, you type in the username/pass once and then you can happily visit any page on the site. Unfortunately this is not the behavior in safari. Every time you go to another page, you must re-enter your credentials. Is there some way I can look at the security exceptions for safari and set it to always trust the certificate or find some other setting to not ask for authentication on each page?

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  • A Look at Exceptions in .NET Applications

    Memory dumps are a wonderful way of finding out what caused an exception in a managed .NET application, particularly if it is happening in a production application. It is when tracking exceptions in applications where you can't use Visual Studio that the techniques of using cdb and sos.dll come into their own. They may nor be skills that you need to use regularly, but at some point, they will be invaluable. Edward supplies sample memory dumps and gives you a simple introduction.

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  • Pragmas and exceptions

    - by Darryl Gove
    The compiler pragmas: #pragma no_side_effect(routinename) #pragma does_not_write_global_data(routinename) #pragma does_not_read_global_data(routinename) are used to tell the compiler more about the routine being called, and enable it to do a better job of optimising around the routine. If a routine does not read global data, then global data does not need to be stored to memory before the call to the routine. If the routine does not write global data, then global data does not need to be reloaded after the call. The no side effect directive indicates that the routine does no I/O, does not read or write global data, and the result only depends on the input. However, these pragmas should not be used on routines that throw exceptions. The following example indicates the problem: #include <iostream extern "C" { int exceptional(int); #pragma no_side_effect(exceptional) } int exceptional(int a) { if (a==7) { throw 7; } else { return a+1; } } int a; int c=0; class myclass { public: int routine(); }; int myclass::routine() { for(a=0; a<1000; a++) { c=exceptional(c); } return 0; } int main() { myclass f; try { f.routine(); } catch(...) { std::cout << "Something happened" << a << c << std::endl; } } The routine "exceptional" is declared as having no side effects, however it can throw an exception. The no side effects directive enables the compiler to avoid storing global data back to memory, and retrieving it after the function call, so the loop containing the call to exceptional is quite tight: $ CC -O -S test.cpp ... .L77000061: /* 0x0014 38 */ call exceptional ! params = %o0 ! Result = %o0 /* 0x0018 36 */ add %i1,1,%i1 /* 0x001c */ cmp %i1,999 /* 0x0020 */ ble,pt %icc,.L77000061 /* 0x0024 */ nop However, when the program is run the result is incorrect: $ CC -O t.cpp $ ./a.out Something happend00 If the code had worked correctly, the output would have been "Something happened77" - the exception occurs on the seventh iteration. Yet, the current code produces a message that uses the original values for the variables 'a' and 'c'. The problem is that the exception handler reads global data, and due to the no side effects directive the compiler has not updated the global data before the function call. So these pragmas should not be used on routines that have the potential to throw exceptions.

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  • The Back Side of Exceptions

    This article illustrates the risks of exceptions being thrown where it is generally not expected, e.g., a library function or a finally block, and shows ways to prevent some insidious errors (such as inconsistency of program data or loss of exception information).

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  • Hidden exceptions

    - by user12617285
    Occasionally you may find yourself in a Java application environment where exceptions in your code are being caught by the application framework and either silently swallowed or converted into a generic exception. Either way, the potentially useful details of your original exception are inaccessible. Wouldn't it be nice if there was a VM option that showed the stack trace for every exception thrown, whether or not it's caught? In fact, HotSpot includes such an option: -XX:+TraceExceptions. However, this option is only available in a debug build of HotSpot (search globals.hpp for TraceExceptions). And based on a quick skim of the HotSpot source code, this option only prints the exception class and message. A more useful capability would be to have the complete stack trace printed as well as the code location catching the exception. This is what the various TraceException* options in in Maxine do (and more). That said, there is a way to achieve a limited version of the same thing with a stock standard JVM. It involves the use of the -Xbootclasspath/p non-standard option. The trick is to modify the source of java.lang.Exception by inserting the following: private static final boolean logging = System.getProperty("TraceExceptions") != null; private void log() { if (logging && sun.misc.VM.isBooted()) { printStackTrace(); } } Then every constructor simply needs to be modified to call log() just before returning: public Exception(String message) { super(message); log(); } public Exception(String message, Throwable cause) { super(message, cause); log(); } // etc... You now need to compile the modified Exception.java source and prepend the resulting class to the boot class path as well as add -DTraceExceptions to your java command line. Here's a console session showing these steps: % mkdir boot % javac -d boot Exception.java % java -DTraceExceptions -Xbootclasspath/p:boot -cp com.oracle.max.vm/bin test.output.HelloWorld java.util.zip.ZipException: error in opening zip file at java.util.zip.ZipFile.open(Native Method) at java.util.zip.ZipFile.(ZipFile.java:127) at java.util.jar.JarFile.(JarFile.java:135) at java.util.jar.JarFile.(JarFile.java:72) at sun.misc.URLClassPath$JarLoader.getJarFile(URLClassPath.java:646) at sun.misc.URLClassPath$JarLoader.access$600(URLClassPath.java:540) at sun.misc.URLClassPath$JarLoader$1.run(URLClassPath.java:607) at java.security.AccessController.doPrivileged(Native Method) at sun.misc.URLClassPath$JarLoader.ensureOpen(URLClassPath.java:599) at sun.misc.URLClassPath$JarLoader.(URLClassPath.java:583) at sun.misc.URLClassPath$3.run(URLClassPath.java:333) at java.security.AccessController.doPrivileged(Native Method) at sun.misc.URLClassPath.getLoader(URLClassPath.java:322) at sun.misc.URLClassPath.getLoader(URLClassPath.java:299) at sun.misc.URLClassPath.getResource(URLClassPath.java:168) at java.net.URLClassLoader$1.run(URLClassLoader.java:194) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at sun.misc.Launcher$ExtClassLoader.findClass(Launcher.java:229) at java.lang.ClassLoader.loadClass(ClassLoader.java:306) at java.lang.ClassLoader.loadClass(ClassLoader.java:295) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:247) java.security.PrivilegedActionException at java.security.AccessController.doPrivileged(Native Method) at sun.misc.URLClassPath$JarLoader.ensureOpen(URLClassPath.java:599) at sun.misc.URLClassPath$JarLoader.(URLClassPath.java:583) at sun.misc.URLClassPath$3.run(URLClassPath.java:333) at java.security.AccessController.doPrivileged(Native Method) at sun.misc.URLClassPath.getLoader(URLClassPath.java:322) ... It's worth pointing out that this is not as useful as direct VM support for tracing exceptions. It has (at least) the following limitations: The trace is shown for every exception, whether it is thrown or not. It only applies to subclasses of java.lang.Exception as there appears to be bootstrap issues when the modification is applied to Throwable.java. It does not show you where the exception was caught. It involves overriding a class in rt.jar, something should never be done in a non-development environment.

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  • Are there legitimate reasons for returning exception objects instead of throwing them?

    - by stakx
    This question is intended to apply to any OO programming language that supports exception handling; I am using C# for illustrative purposes only. Exceptions are usually intended to be raised when an problem arises that the code cannot immediately handle, and then to be caught in a catch clause in a different location (usually an outer stack frame). Q: Are there any legitimate situations where exceptions are not thrown and caught, but simply returned from a method and then passed around as error objects? This question came up for me because .NET 4's System.IObserver<T>.OnError method suggests just that: exceptions being passed around as error objects. Let's look at another scenario, validation. Let's say I am following conventional wisdom, and that I am therefore distinguishing between an error object type IValidationError and a separate exception type ValidationException that is used to report unexpected errors: partial interface IValidationError { } abstract partial class ValidationException : System.Exception { public abstract IValidationError[] ValidationErrors { get; } } (The System.Component.DataAnnotations namespace does something quite similar.) These types could be employed as follows: partial interface IFoo { } // an immutable type partial interface IFooBuilder // mutable counterpart to prepare instances of above type { bool IsValid(out IValidationError[] validationErrors); // true if no validation error occurs IFoo Build(); // throws ValidationException if !IsValid(…) } Now I am wondering, could I not simplify the above to this: partial class ValidationError : System.Exception { } // = IValidationError + ValidationException partial interface IFoo { } // (unchanged) partial interface IFooBuilder { bool IsValid(out ValidationError[] validationErrors); IFoo Build(); // may throw ValidationError or sth. like AggregateException<ValidationError> } Q: What are the advantages and disadvantages of these two differing approaches?

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  • How to handle uncaught Exceptions in javascript without a try/catch-block?

    - by user344238
    What i try to accomplish is to register a global handler to catch all uncaught exceptions. Searching the web i only managed to find people pointing out window.onerror but this doesn't do the trick for me. Apparently window.onerror only gets called upon errors and not upon exceptions. Assume the following code: function windowError(message, url, line) { alert(message, url, line); } window.onerror=windowError; throw("uncaught"); The obviously uncaught exception won't trigger the windowError handler. (Using Firefox 3.6.3) Any suggestions?

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  • How to document thrown exceptions in c#/.net

    - by Arnold Zokas
    I am currently writing a small framework that will be used internally by other developers within the company. I want to provide good Intellisense information, but I am not sure how to document thrown exceptions. In the following example: public void MyMethod1() { MyMethod2(); // also may throw InvalidOperationException } public void MyMethod2() { System.IO.File.Open(somepath...); // this may throw FileNotFoundException // also may throw DivideByZeroException } I know the markup for documenting exceptions is: /// <exception cref="SomeException">when things go wrong.</exception> What I don't understand is how to document exceptions thrown by code called by MyMethod1()? Should I document exceptions thrown by MyMethod2() Should I document exceptions thrown by File.Open() ? What would be the best way to document possible exceptions?

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  • Exception is swallowed by finally

    - by fiction
    static int retIntExc() throws Exception{ int result = 1; try { result = 2; throw new IOException("Exception rised."); } catch (ArrayIndexOutOfBoundsException e) { System.out.println(e.getMessage()); result = 3; } finally { return result; } } A friend of mine is a .NET developer and currently migrating to Java and he ask me the following question about this source. In theory this must throw IOException("Exception rised.") and the whole method retIntExc() must throws Exception. But nothing happens, the method returns 2. I've not tested his example, but I think that this isn't the expected behavior. EDIT: Thanks for all answers. Some of you have ignored the fact that method is called retIntExc, which means that this is only some test/experimental example, showing problem in throwing/catching mechanics. I didn't need 'fix', I needed explanation why this happens.

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  • Header Guard Issues - Getting Swallowed Alive

    - by gjnave
    I'm totally at wit's end: I can't figure out how my dependency issues. I've read countless posts and blogs and reworked my code so many times that I can't even remember what almost worked and what didnt. I continually get not only redefinition errors, but class not defined errors. I rework the header guards and remove some errors simply to find others. I somehow got everything down to one error but then even that got broke while trying to fix it. Would you please help me figure out the problem? card.cpp #include <iostream> #include <cctype> #include "card.h" using namespace std; // ====DECL====== Card::Card() { abilities = 0; flavorText = 0; keywords = 0; artifact = 0; classType = new char[strlen("Card") + 1]; classType = "Card"; } Card::~Card (){ delete name; delete abilities; delete flavorText; artifact = NULL; } // ------------ Card::Card(const Card & to_copy) { name = new char[strlen(to_copy.name) +1]; // creating dynamic array strcpy(to_copy.name, name); type = to_copy.type; color = to_copy.color; manaCost = to_copy.manaCost; abilities = new char[strlen(to_copy.abilities) +1]; strcpy(abilities, to_copy.abilities); flavorText = new char[strlen(to_copy.flavorText) +1]; strcpy(flavorText, to_copy.flavorText); keywords = new char[strlen(to_copy.keywords) +1]; strcpy(keywords, to_copy.keywords); inPlay = to_copy.inPlay; tapped = to_copy.tapped; enchanted = to_copy.enchanted; cursed = to_copy.cursed; if (to_copy.type != ARTIFACT) artifact = to_copy.artifact; } // ====DECL===== int Card::equipArtifact(Artifact* to_equip){ artifact = to_equip; } Artifact * Card::unequipArtifact(Card * unequip_from){ Artifact * to_remove = artifact; artifact = NULL; return to_remove; // put card in hand or in graveyard } int Card::enchant( Card * to_enchant){ to_enchant->enchanted = true; cout << "enchanted" << endl; } int Card::disenchant( Card * to_disenchant){ to_disenchant->enchanted = false; cout << "Enchantment Removed" << endl; } // ========DECL===== Spell::Spell() { currPower = basePower; currToughness = baseToughness; classType = new char[strlen("Spell") + 1]; classType = "Spell"; } Spell::~Spell(){} // --------------- Spell::Spell(const Spell & to_copy){ currPower = to_copy.currPower; basePower = to_copy.basePower; currToughness = to_copy.currToughness; baseToughness = to_copy.baseToughness; } // ========= int Spell::attack( Spell *& blocker ){ blocker->currToughness -= currPower; currToughness -= blocker->currToughness; } //========== int Spell::counter (Spell *& to_counter){ cout << to_counter->name << " was countered by " << name << endl; } // ============ int Spell::heal (Spell *& to_heal, int amountOfHealth){ to_heal->currToughness += amountOfHealth; } // ------- Creature::Creature(){ summoningSick = true; } // =====DECL====== Land::Land(){ color = NON; classType = new char[strlen("Land") + 1]; classType = "Land"; } // ------ int Land::generateMana(int mana){ // ... // } card.h #ifndef CARD_H #define CARD_H #include <cctype> #include <iostream> #include "conception.h" class Artifact; class Spell; class Card : public Conception { public: Card(); Card(const Card &); ~Card(); protected: char* name; enum CardType { INSTANT, CREATURE, LAND, ENCHANTMENT, ARTIFACT, PLANESWALKER}; enum CardColor { WHITE, BLUE, BLACK, RED, GREEN, NON }; CardType type; CardColor color; int manaCost; char* abilities; char* flavorText; char* keywords; bool inPlay; bool tapped; bool cursed; bool enchanted; Artifact* artifact; virtual int enchant( Card * ); virtual int disenchant (Card * ); virtual int equipArtifact( Artifact* ); virtual Artifact* unequipArtifact(Card * ); }; // ------------ class Spell: public Card { public: Spell(); ~Spell(); Spell(const Spell &); protected: virtual int heal( Spell *&, int ); virtual int attack( Spell *& ); virtual int counter( Spell*& ); int currToughness; int baseToughness; int currPower; int basePower; }; class Land: public Card { public: Land(); ~Land(); protected: virtual int generateMana(int); }; class Forest: public Land { public: Forest(); ~Forest(); protected: int generateMana(); }; class Creature: public Spell { public: Creature(); ~Creature(); protected: bool summoningSick; }; class Sorcery: public Spell { public: Sorcery(); ~Sorcery(); protected: }; #endif conception.h -- this is an "uber class" from which everything derives class Conception{ public: Conception(); ~Conception(); protected: char* classType; }; conception.cpp Conception::Conception{ Conception(){ classType = new char[11]; char = "Conception"; } game.cpp -- this is an incomplete class as of this code #include <iostream> #include <cctype> #include "game.h" #include "player.h" Battlefield::Battlefield(){ card = 0; } Battlefield::~Battlefield(){ delete card; } Battlefield::Battlefield(const Battlefield & to_copy){ } // =========== /* class Game(){ public: Game(); ~Game(); protected: Player** player; // for multiple players Battlefield* root; // for battlefield getPlayerMove(); // ask player what to do addToBattlefield(); removeFromBattlefield(); sendAttack(); } */ #endif game.h #ifndef GAME_H #define GAME_H #include "list.h" class CardList(); class Battlefield : CardList{ public: Battlefield(); ~Battlefield(); protected: Card* card; // make an array }; class Game : Conception{ public: Game(); ~Game(); protected: Player** player; // for multiple players Battlefield* root; // for battlefield getPlayerMove(); // ask player what to do addToBattlefield(); removeFromBattlefield(); sendAttack(); Battlefield* field; }; list.cpp #include <iostream> #include <cctype> #include "list.h" // ========== LinkedList::LinkedList(){ root = new Node; classType = new char[strlen("LinkedList") + 1]; classType = "LinkedList"; }; LinkedList::~LinkedList(){ delete root; } LinkedList::LinkedList(const LinkedList & obj) { // code to copy } // --------- // ========= int LinkedList::delete_all(Node* root){ if (root = 0) return 0; delete_all(root->next); root = 0; } int LinkedList::add( Conception*& is){ if (root == 0){ root = new Node; root->next = 0; } else { Node * curr = root; root = new Node; root->next=curr; root->it = is; } } int LinkedList::remove(Node * root, Node * prev, Conception* is){ if (root = 0) return -1; if (root->it == is){ root->next = root->next; return 0; } remove(root->next, root, is); return 0; } Conception* LinkedList::find(Node*& root, const Conception* is, Conception* holder = NULL) { if (root==0) return NULL; if (root->it == is){ return root-> it; } holder = find(root->next, is); return holder; } Node* LinkedList::goForward(Node * root){ if (root==0) return root; if (root->next == 0) return root; else return root->next; } // ============ Node* LinkedList::goBackward(Node * root){ root = root->prev; } list.h #ifndef LIST_H #define LIST_H #include <iostream> #include "conception.h" class Node : public Conception { public: Node() : next(0), prev(0), it(0) { it = 0; classType = new char[strlen("Node") + 1]; classType = "Node"; }; ~Node(){ delete it; delete next; delete prev; } Node* next; Node* prev; Conception* it; // generic object }; // ---------------------- class LinkedList : public Conception { public: LinkedList(); ~LinkedList(); LinkedList(const LinkedList&); friend bool operator== (Conception& thing_1, Conception& thing_2 ); protected: virtual int delete_all(Node*); virtual int add( Conception*& ); // virtual Conception* find(Node *&, const Conception*, Conception* ); // virtual int remove( Node *, Node *, Conception* ); // removes question with keyword int display_all(node*& ); virtual Node* goForward(Node *); virtual Node* goBackward(Node *); Node* root; // write copy constrcutor }; // ============= class CircularLinkedList : public LinkedList { public: // CircularLinkedList(); // ~CircularLinkedList(); // CircularLinkedList(const CircularLinkedList &); }; class DoubleLinkedList : public LinkedList { public: // DoubleLinkedList(); // ~DoubleLinkedList(); // DoubleLinkedList(const DoubleLinkedList &); protected: }; // END OF LIST Hierarchy #endif player.cpp #include <iostream> #include "player.h" #include "list.h" using namespace std; Library::Library(){ root = 0; } Library::~Library(){ delete card; } // ====DECL========= Player::~Player(){ delete fname; delete lname; delete deck; } Wizard::~Wizard(){ delete mana; delete rootL; delete rootH; } // =====Player====== void Player::changeName(const char[] first, const char[] last){ char* backup1 = new char[strlen(fname) + 1]; strcpy(backup1, fname); char* backup2 = new char[strlen(lname) + 1]; strcpy(backup1, lname); if (first != NULL){ fname = new char[strlen(first) +1]; strcpy(fname, first); } if (last != NULL){ lname = new char[strlen(last) +1]; strcpy(lname, last); } return 0; } // ========== void Player::seeStats(Stats*& to_put){ to_put->wins = stats->wins; to_put->losses = stats->losses; to_put->winRatio = stats->winRatio; } // ---------- void Player::displayDeck(const LinkedList* deck){ } // ================ void CardList::findCard(Node* root, int id, NodeCard*& is){ if (root == NULL) return; if (root->it.id == id){ copyCard(root->it, is); return; } else findCard(root->next, id, is); } // -------- void CardList::deleteAll(Node* root){ if (root == NULL) return; deleteAll(root->next); root->next = NULL; } // --------- void CardList::removeCard(Node* root, int id){ if (root == NULL) return; if (root->id = id){ root->prev->next = root->next; // the prev link of root, looks back to next of prev node, and sets to where root next is pointing } return; } // --------- void CardList::addCard(Card* to_add){ if (!root){ root = new Node; root->next = NULL; root->prev = NULL; root->it = &to_add; return; } else { Node* original = root; root = new Node; root->next = original; root->prev = NULL; original->prev = root; } } // ----------- void CardList::displayAll(Node*& root){ if (root == NULL) return; cout << "Card Name: " << root->it.cardName; cout << " || Type: " << root->it.type << endl; cout << " --------------- " << endl; if (root->classType == "Spell"){ cout << "Base Power: " << root->it.basePower; cout << " || Current Power: " << root->it.currPower << endl; cout << "Base Toughness: " << root->it.baseToughness; cout << " || Current Toughness: " << root->it.currToughness << endl; } cout << "Card Type: " << root->it.currPower; cout << " || Card Color: " << root->it.color << endl; cout << "Mana Cost" << root->it.manaCost << endl; cout << "Keywords: " << root->it.keywords << endl; cout << "Flavor Text: " << root->it.flavorText << endl; cout << " ----- Class Type: " << root->it.classType << " || ID: " << root->it.id << " ----- " << endl; cout << " ******************************************" << endl; cout << endl; // ------- void CardList::copyCard(const Card& to_get, Card& put_to){ put_to.type = to_get.type; put_to.color = to_get.color; put_to.manaCost = to_get.manaCost; put_to.inPlay = to_get.inPlay; put_to.tapped = to_get.tapped; put_to.class = to_get.class; put_to.id = to_get.id; put_to.enchanted = to_get.enchanted; put_to.artifact = to_get.artifact; put_to.class = to_get.class; put.to.abilities = new char[strlen(to_get.abilities) +1]; strcpy(put_to.abilities, to_get.abilities); put.to.keywords = new char[strlen(to_get.keywords) +1]; strcpy(put_to.keywords, to_get.keywords); put.to.flavorText = new char[strlen(to_get.flavorText) +1]; strcpy(put_to.flavorText, to_get.flavorText); if (to_get.class = "Spell"){ put_to.baseToughness = to_get.baseToughness; put_to.basePower = to_get.basePower; put_to.currToughness = to_get.currToughness; put_to.currPower = to_get.currPower; } } // ---------- player.h #ifndef player.h #define player.h #include "list.h" // ============ class CardList() : public LinkedList(){ public: CardList(); ~CardList(); protected: virtual void findCard(Card&); virtual void addCard(Card* ); virtual void removeCard(Node* root, int id); virtual void deleteAll(); virtual void displayAll(); virtual void copyCard(const Conception*, Node*&); Node* root; } // --------- class Library() : public CardList(){ public: Library(); ~Library(); protected: Card* card; int numCards; findCard(Card&); // get Card and fill empty template } // ----------- class Deck() : public CardList(){ public: Deck(); ~Deck(); protected: enum deckColor { WHITE, BLUE, BLACK, RED, GREEN, MIXED }; char* deckName; } // =============== class Mana(int amount) : public Conception { public: Mana() : displayTotal(0), classType(0) { displayTotal = 0; classType = new char[strlen("Mana") + 1]; classType = "Mana"; }; protected: int accrued; void add(); void remove(); int displayTotal(); } inline Mana::add(){ accrued += 1; } inline Mana::remove(){ accrued -= 1; } inline Mana::displayTotal(){ return accrued; } // ================ class Stats() : public Conception { public: friend class Player; friend class Game; Stats() : wins(0), losses(0), winRatio(0) { wins = 0; losses = 0; if ( (wins + losses != 0) winRatio = wins / (wins + losses); else winRatio = 0; classType = new char[strlen("Stats") + 1]; classType = "Stats"; } protected: int wins; int losses; float winRatio; void int getStats(Stats*& ); } // ================== class Player() : public Conception{ public: Player() : wins(0), losses(0), winRatio(0) { fname = NULL; lname = NULL; stats = NULL; CardList = NULL; classType = new char[strlen("Player") + 1]; classType = "Player"; }; ~Player(); Player(const Player & obj); protected: // member variables char* fname; char* lname; Stats stats; // holds previous game statistics CardList* deck[]; // hold multiple decks that player might use - put ll in this private: // member functions void changeName(const char[], const char[]); void shuffleDeck(int); void seeStats(Stats*& ); void displayDeck(int); chooseDeck(); } // -------------------- class Wizard(Card) : public Player(){ public: Wizard() : { mana = NULL; rootL = NULL; rootH = NULL}; ~Wizard(); protected: playCard(const Card &); removeCard(Card &); attackWithCard(Card &); enchantWithCard(Card &); disenchantWithCard(Card &); healWithCard(Card &); equipWithCard(Card &); Mana* mana[]; Library* rootL; // Library Library* rootH; // Hand } #endif

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  • Handling EJB/JPA exceptions in a “beautiful” way

    - by Rodrigues, Raphael
    In order to handle JPA exceptions, there are some ways already detailed in lots of blogs. Here, I intend to show one of them, which I consider kind of “beauty”. My use case has a unique constraint, when the User try to create a duplicate value in database. The JPA throws a java.sql.SQLIntegrityConstraintViolationException, and I have to catch it and replace the message. In fact, ADF Business Components framework already has a beautiful solution for this very well documented here . However, for EJB/JPA there's no similar approach. In my case, what I had to do was: 1. Create a custom Error Handler Class in DataBindings file; a. Here is how you accomplish it. 2. Override the reportException method and check if the type of exception exists on property file a. If yes, I change the message and rethrows the exception b. If not, go on the execution The main goal of this approach is whether a new or unhandled Exception was raised, the job is, only create a single entry in bundle property file. Here are pictures step by step: 1. CustomExceptionHandler.java 2. Databindings.cpx 3. Bundle file 4. jspx: 5. Stacktrace: Give your opinion, what did you think about that?

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  • Scenarios for Throwing Exceptions

    - by Joe Mayo
    I recently came across a situation where someone had an opinion that differed from mine of when an exception should be thrown. This particular case was an issue opened on LINQ to Twitter for an Exception on EndSession.  The premise of the issue was that the poster didn’t feel an exception should be raised, regardless of authentication status.  As first, this sounded like a valid point.  However, I went back to review my code and decided not to make any changes. Here's my rationale: 1. The exception doesn’t occur if the user is authenticated when EndAccountSession is called. 2. The exception does occur if the user is not authenticated when EndAccountSession is called. 3. The exception represents the fact that EndAccountSession is not able to fulfill its intended purpose - to end the session.  If a session never existed, then it would not be possible to perform the requested action.  Therefore, an exception is appropriate. To help illustrate how to handle this situation, I've modified the following code in Program.cs in the LinqToTwitterDemo project to illustrate the situation: static void EndSession(ITwitterAuthorizer auth) { using (var twitterCtx = new TwitterContext(auth, "https://api.twitter.com/1/", "https://search.twitter.com/")) { try { //Log twitterCtx.Log = Console.Out; var status = twitterCtx.EndAccountSession(); Console.WriteLine("Request: {0}, Error: {1}" , status.Request , status.Error); } catch (TwitterQueryException tqe) { var webEx = tqe.InnerException as WebException; if (webEx != null) { var webResp = webEx.Response as HttpWebResponse; if (webResp != null && webResp.StatusCode == HttpStatusCode.Unauthorized) Console.WriteLine("Twitter didn't recognize you as having been logged in. Therefore, your request to end session is illogical.\n"); } var status = tqe.Response; Console.WriteLine("Request: {0}, Error: {1}" , status.Request , status.Error); } } } As expected, LINQ to Twitter wraps the exception in a TwitterQueryException as the InnerException.  The TwitterQueryException serves a very useful purpose through it's Response property.  Notice in the example above that the response has Request and Error proprieties.  These properties correspond to the information that Twitter returns as part of it's response payload.  This is often useful while debugging to help you understand why Twitter was unable to perform the  requested action.  Other times, it's cryptic, but that's another story.  At least you have some way of knowing in your code how to anticipate and handle these situations, along with having extra information to debug with. To sum things up, there are two points to make: when and why an exception should be raised and when to wrap and re-throw an exception in a custom exception type. I felt it was necessary to allow the exception to be raised because the called method was unable to perform the task it was designed for.  I also felt that it is inappropriate for a general library to do anything with exceptions because that could potentially hide a problem from the caller.  A related point is that it should be the exclusive decision of the application that uses the library on what to do with an exception.  Another aspect of this situation is that I wrapped the exception in a custom exception and re-threw.  This is a tough call because I don’t want to hide any stack trace information.  However, the need to make the exception more meaningful by including vital information returned from Twitter swayed me in the direction to design an interface that was as helpful as possible to library consumers.  As shown in the code above, you can dig into the exception and pull out a lot of good information, such as the fact that the underlying HTTP response was a 401 Unauthorized.  In all, trade-offs are seldom perfect for all cases, but combining the fact that the method was unable to perform its intended function, this is a library, and the extra information can be more helpful, it seemed to be the better design. @JoeMayo

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  • Green Exceptions?

    - by Aren B
    When unhandled exceptions are encountered in VStudio usually the debugger highlights the line YELLOW as the line that threw the exception. However sometimes I encounter exceptions where the debugger highlights them green as shown: I've always treated them as normal exceptions, but today I decided to ask since google/bing produced no results for "Visual Studio Green Exceptions"

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  • Exceptions silently caught by Windows, how to handle manually?

    - by Mark Ingram
    We're having problems with Windows silently eating exceptions and allowing the application to continue running, when the exception is thrown inside the message pump. For example, we created a test MFC MDI application, and overrode OnDraw: void CTestView::OnDraw(CDC* /*pDC*/) { *(int*)0 = 0; // Crash CTestDoc* pDoc = GetDocument(); ASSERT_VALID(pDoc); if (!pDoc) return; // TODO: add draw code for native data here } You would expect a nasty error message when running the application, but you actually get nothing at all. The program appears to be running perfectly well, but if you check the output window you will see: First-chance exception at 0x13929384 in Test.exe: 0xC0000005: Access violation writing location 0x00000000. First-chance exception at 0x77c6ee42 in Test.exe: 0xC0150010: The activation context being deactivated is not active for the current thread of execution. I know why I'm receiving the application context exception, but why is it being handled silently? It means our applications could be suffering serious problems when in use, but we'll never know about it, because our users will never report any problems.

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  • How do I make VC++'s debugger break on exceptions?

    - by Mason Wheeler
    I'm trying to debug a problem in a DLL written in C that keeps causing access violations. I'm using Visual C++ 2008, but the code is straight C. I'm used to Delphi, where if an exception occurs while running under the debugger, the program will immediately break to the debugger and it will give you a chance to examine the program state. In Visual C++, though, all I get is a message in the Output tab: First-chance exception at blah blah blah: Access violation reading location 0x04410000. No breaks, nothing. It just goes and unwinds the stack until it's back in my Delphi EXE, which recognizes something's wrong and alerts me there, but by that point I've lost several layers of call stack and I don't know what's going on. I've tried other debugging techniques, but whatever it's doing is taking place deep within a nested loop inside a C macro that's getting called more than 500 times, and that's just a bit beyond my skill (or my patience) to trace through. I figure there has to be some way to get the "first-chance" exception to actually give me a "chance" to handle it. There's probably some "break immediately on first-chance exceptions" configuration setting I don't know about, but it doesn't seem to be all that discoverable. Does anyone know where it is and how to enable it?

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  • How to differentiate between exceptions i can show the user, and ones i can't?

    - by Ian Boyd
    i have some business logic that traps some logically invalid situations, e.g. trying to reverse a transaction that was already reversed. In this case the correct action is to inform the user: Transaction already reversed or Cannot reverse a reversing transaction or You do not have permission to reverse transactions or This transaction is on a session that has already been closed or This transaction is too old to be reversed The question is, how do i communicate these exceptional cases back to the calling code, so they can show the user? Do i create a separate exception for each case: catch (ETransactionAlreadyReversedException) MessageBox.Show('Transaction already reversed') catch (EReversingAReversingTransactionException) MessageBox.Show('Cannot reverse a reversing transaction') catch (ENoPermissionToReverseTranasctionException) MessageBox.Show('You do not have permission to reverse transactions') catch (ECannotReverseTransactionOnAlredyClosedSessionException) MessageBox.Show('This transaction is on a session that has already been closed') catch (ECannotReverseTooOldTransactionException) MessageBox.Show('This transaction is too old to be reversed') Downside for this is that when there's a new logical case to show the user: Tranasctions created by NSL cannot be reversed i don't simply show the user a message, and instead it leaks out as an unhandled excpetion, when really it should be handled with another MessageBox. The alternative is to create a single exception class: `EReverseTransactionException` With the understanding that any exception of this type is a logical check, that should be handled with a message box: catch (EReverseTransactionException) But it's still understood that any other exceptions, ones that involve, for example, an memory ECC parity error, continue unhandled. In other words, i don't convert all errors that can be thrown by the ReverseTransaction() method into EReverseTransactionException, only ones that are logically invalid cause of the user.

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  • in which namespace / package to put exceptions

    - by Fabiano
    Hi What is the common or best practice to structure the location of your exception classes? Let's say you have the packages/namespaces myproject.person (models and DAOs for persons) and myproject.order (models and DAOs for orders) and the exceptions PersonException and OrderException. Should I put the exceptions in their corresponding packages or in a separate package for exceptions (e.g. myproject.exceptions)? The first approach seems more reasonable (because it's sorted by functionality). But there the question arises where you should put exceptions that are related to both? e.g. a ConstraintViolationException Thanks

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  • SWIG: Throwing exceptions from Python to C++

    - by wheaties
    We've got an interface we've defined in C++ (abstract class, all functions pure virtual) which will be extended in Python. To overcome the cross-language polymorphism issues we're planning on using SWIG directors. I've read how to catch exceptions thrown from C++ code in our Python code here, here, here, and even on SO. It's fairly straight forward and I'm not expecting issues with handling our library's own exceptions. What I'd like to know and can't seem to find in the documentation is how to have our Python implementation of the extended C++ interface throw those C++ exceptions in a way that makes them visible to the C++ code. We could make small functions within the *.i files such that each function throws our exceptions: void throw_myException(){ throw MyException; } but I'm wondering how it will interact with the Python code. Anyone have any experience with throwing C++ exceptions from Python code?

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  • Throwing exception from a property when my object state is invalid

    - by Rumi P.
    Microsoft guidelines say: "Avoid throwing exceptions from property getters", and I normally follow that. But my application uses Linq2SQL, and there is the case where my object can be in invalid state because somebody or something wrote nonsense into the database. Consider this toy example: [Table(Name="Rectangle")] public class Rectangle { [Column(Name="ID", IsPrimaryKey = true, IsDbGenerated = true)] public int ID {get; set;} [Column(Name="firstSide")] public double firstSide {get; set;} [Column(Name="secondSide")] public double secondSide {get; set;} public double sideRatio { get { return firstSide/secondSide; } } } Here, I could write code which ensures that my application never writes a Rectangle with a zero-length side into the database. But no matter how bulletproof I make my own code, somebody could open the database with a different application and create an invalid Rectangle, especially one with a 0 for secondSide. (For this example, please forget that it is possible to design the database in a way such that writing a side length of zero into the rectangle table is impossible; my domain model is very complex and there are constraints on model state which cannot be expressed in a relational database). So, the solution I am gravitating to is to change the getter to: get { if(firstSide > 0 && secondSide > 0) return firstSide/secondSide; else throw new System.InvalidOperationException("All rectangle sides should have a positive length"); } The reasoning behind not throwing exceptions from properties is that programmers should be able to use them without having to make precautions about catching and handling them them. But in this case, I think that it is OK to continue to use this property without such precautions: if the exception is thrown because my application wrote a non-zero rectangle side into the database, then this is a serious bug. It cannot and shouldn't be handled in the application, but there should be code which prevents it. It is good that the exception is visibly thrown, because that way the bug is caught. if the exception is thrown because a different application changed the data in the database, then handling it is outside of the scope of my application. So I can't do anything about it if I catch it. Is this a good enough reasoning to get over the "avoid" part of the guideline and throw the exception? Or should I turn it into a method after all? Note that in the real code, the properties which can have an invalid state feel less like the result of a calculation, so they are "natural" properties, not methods.

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  • How to deal with checked exceptions that cannot ever be thrown

    - by ammoQ
    Example: foobar = new InputStreamReader(p.getInputStream(), "ISO-8859-1"); Since the encoding is hardcoded and correct, the constructor will never throw the UnsupportedEncodingException declared in the specification (unless the java implementation is broken, in which case I'm lost anyway). Anyway, Java forces me to deal with that exception anyway. Currently, it looks like that try { foobar = new InputStreamReader(p.getInputStream(), "ISO-8859-1"); } catch(UnsupportedEncodingException e) { /* won't ever happen */ } Any ideas how to make it better?

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  • Printing Tip Handling User Initiated Dialogs Exceptions

    I see this question every so often so it makes sense to share it through a quick post. When using the print API in Silverlight 4 you can run into the dreaded exception: System.Security.SecurityException: Dialogs must be user-initiated Then you examine your code and confirm that your code where you invoke the PrintDocuments Print method are indeed being handled by a user-initiated event. If you are not invoking Print in a user-initiated event then your know your solution :) Here is some sample...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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