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  • C++ require that one template type is derived from the other

    - by Will
    In a comparison operator: template<class R1, class R2> bool operator==(Manager<R1> m1, Manager<R2> m2) { return p1.internal_field == p2.internal_field; } Is there any way I could enforce that R1 and R2 must have a supertype or subtype relation? That is, I'd like to allow either R1 to be derived from R2, or R2 to be derived from R1, but disallow the comparison if R1 and R2 are unrelated types.

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  • Design by Contract with Microsoft .Net Code Contract

    - by Fredrik N
    I have done some talks on different events and summits about Defensive Programming and Design by Contract, last time was at Cornerstone’s Developer Summit 2010. Next time will be at SweNug (Sweden .Net User Group). I decided to write a blog post about of some stuffs I was talking about. Users are a terrible thing! Protect your self from them ”Human users have a gift for doing the worst possible thing at the worst possible time.” – Michael T. Nygard, Release It! The kind of users Michael T. Nygard are talking about is the users of a system. We also have users that uses our code, the users I’m going to focus on is the users of our code. Me and you and another developers. “Any fool can write code that a computer can understand. Good programmers write code that humans can understand.” – Martin Fowler Good programmers also writes code that humans know how to use, good programmers also make sure software behave in a predictable manner despise inputs or user actions. Design by Contract   Design by Contract (DbC) is a way for us to make a contract between us (the code writer) and the users of our code. It’s about “If you give me this, I promise to give you this”. It’s not about business validations, that is something completely different that should be part of the domain model. DbC is to make sure the users of our code uses it in a correct way, and that we can rely on the contract and write code in a way where we know that the users will follow the contract. It will make it much easier for us to write code with a contract specified. Something like the following code is something we may see often: public void DoSomething(Object value) { value.DoIKnowThatICanDoThis(); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Where “value” can be uses directly or passed to other methods and later be used. What some of us can easily forget here is that the “value” can be “null”. We will probably not passing a null value, but someone else that uses our code maybe will do it. I think most of you (including me) have passed “null” into a method because you don’t know if the argument need to be specified to a valid value etc. I bet most of you also have got the “Null reference exception”. Sometimes this “Null reference exception” can be hard and take time to fix, because we need to search among our code to see where the “null” value was passed in etc. Wouldn’t it be much better if we can as early as possible specify that the value can’t not be null, so the users of our code also know it when the users starts to use our code, and before run time execution of the code? This is where DbC comes into the picture. We can use DbC to specify what we need, and by doing so we can rely on the contract when we write our code. So the code above can actually use the DoIKnowThatICanDoThis() method on the value object without being worried that the “value” can be null. The contract between the users of the code and us writing the code, says that the “value” can’t be null.   Pre- and Postconditions   When working with DbC we are specifying pre- and postconditions.  Precondition is a condition that should be met before a query or command is executed. An example of a precondition is: “The Value argument of the method can’t be null”, and we make sure the “value” isn’t null before the method is called. Postcondition is a condition that should be met when a command or query is completed, a postcondition will make sure the result is correct. An example of a postconditon is “The method will return a list with at least 1 item”. Commands an Quires When using DbC, we need to know what a Command and a Query is, because some principles that can be good to follow are based on commands and queries. A Command is something that will not return anything, like the SQL’s CREATE, UPDATE and DELETE. There are two kinds of Commands when using DbC, the Creation commands (for example a Constructor), and Others. Others can for example be a Command to add a value to a list, remove or update a value etc. //Creation commands public Stack(int size) //Other commands public void Push(object value); public void Remove(); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   A Query, is something that will return something, for example an Attribute, Property or a Function, like the SQL’s SELECT.   There are two kinds of Queries, the Basic Queries  (Quires that aren’t based on another queries), and the Derived Queries, queries that is based on another queries. Here is an example of queries of a Stack: //Basic Queries public int Count; public object this[int index] { get; } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } To understand about some principles that are good to follow when using DbC, we need to know about the Commands and different Queries. The 6 Principles When working with DbC, it’s advisable to follow some principles to make it easier to define and use contracts. The following DbC principles are: Separate commands and queries. Separate basic queries from derived queries. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries. For each command, write a postcondition that specifies the value of every basic query. For every query and command, decide on a suitable precondition. Write invariants to define unchanging properties of objects. Before I will write about each of them I want you to now that I’m going to use .Net 4.0 Code Contract. I will in the rest of the post uses a simple Stack (Yes I know, .Net already have a Stack class) to give you the basic understanding about using DbC. A Stack is a data structure where the first item in, will be the first item out. Here is a basic implementation of a Stack where not contract is specified yet: public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } //Is related to Count and this[] Query public object Top() { return this[Count]; } //Creation commands public Stack(uint size) { Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { this[++Count] = value; } public void Remove() { this[Count] = null; Count--; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The Stack is implemented in a way to demonstrate the use of Code Contract in a simple way, the implementation may not look like how you would implement it, so don’t think this is the perfect Stack implementation, only used for demonstration.   Before I will go deeper into the principles I will simply mention how we can use the .Net Code Contract. I mention before about pre- and postcondition, is about “Require” something and to “Ensure” something. When using Code Contract, we will use a static class called “Contract” and is located in he “System.Diagnostics.Contracts” namespace. The contract must be specified at the top or our member statement block. To specify a precondition with Code Contract we uses the Contract.Requires method, and to specify a postcondition, we uses the Contract.Ensure method. Here is an example where both a pre- and postcondition are used: public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The contract above requires that the Count is greater than 0, if not we can’t get the item at the Top of a Stack. We also Ensures that the results (By using the Contract.Result method, we can specify a postcondition that will check if the value returned from a method is correct) of the Top query is equal to this[Count].   1. Separate Commands and Queries   When working with DbC, it’s important to separate Command and Quires. A method should either be a command that performs an Action, or returning information to the caller, not both. By asking a question the answer shouldn’t be changed. The following is an example of a Command and a Query of a Stack: public void Push(object value) public object Top() .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   The Push is a command and will not return anything, just add a value to the Stack, the Top is a query to get the item at the top of the stack.   2. Separate basic queries from derived queries There are two different kinds of queries,  the basic queries that doesn’t rely on another queries, and derived queries that uses a basic query. The “Separate basic queries from derived queries” principle is about about that derived queries can be specified in terms of basic queries. So this principles is more about recognizing that a query is a derived query or a basic query. It will then make is much easier to follow the other principles. The following code shows a basic query and a derived query: //Basic Queries public uint Count; //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   We can see that IsEmpty will use the Count query, and that makes the IsEmpty a Derived query.   3. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries.   When the derived query is recognize we can follow the 3ed principle. For each derived query, we can create a postcondition that specifies what result our derived query will return in terms of one or more basic queries. Remember that DbC is about contracts between the users of the code and us writing the code. So we can’t use demand that the users will pass in a valid value, we must also ensure that we will give the users what the users wants, when the user is following our contract. The IsEmpty query of the Stack will use a Count query and that will make the IsEmpty a Derived query, so we should now write a postcondition that specified what results will be returned, in terms of using a basic query and in this case the Count query, //Basic Queries public uint Count; //Derived Queries public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } The Contract.Ensures is used to create a postcondition. The above code will make sure that the results of the IsEmpty (by using the Contract.Result to get the result of the IsEmpty method) is correct, that will say that the IsEmpty will be either true or false based on Count is equal to 0 or not. The postcondition are using a basic query, so the IsEmpty is now following the 3ed principle. We also have another Derived Query, the Top query, it will also need a postcondition and it uses all basic queries. The Result of the Top method must be the same value as the this[] query returns. //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count and this[] Query public object Top() { Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   4. For each command, write a postcondition that specifies the value of every basic query.   For each command we will create a postconditon that specifies the value of basic queries. If we look at the Stack implementation we will have three Commands, one Creation command, the Constructor, and two others commands, Push and Remove. Those commands need a postcondition and they should include basic query to follow the 4th principle. //Creation commands public Stack(uint size) { Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   As you can see the Create command will Ensures that Count will be 0 when the Stack is created, when a Stack is created there shouldn’t be any items in the stack. The Push command will take a value and put it into the Stack, when an item is pushed into the Stack, the Count need to be increased to know the number of items added to the Stack, and we must also make sure the item is really added to the Stack. The postconditon of the Push method will make sure the that old value of the Count (by using the Contract.OldValue we can get the value a Query has before the method is called)  plus 1 will be equal to the Count query, this is the way we can ensure that the Push will increase the Count with one. We also make sure the this[] query will now contain the item we pushed into the Stack. The Remove method must make sure the Count is decreased by one when the top item is removed from the Stack. The Commands is now following the 4th principle, where each command now have a postcondition that used the value of basic queries. Note: The principle says every basic Query, the Remove only used one Query the Count, it’s because this command can’t use the this[] query because an item is removed, so the only way to make sure an item is removed is to just use the Count query, so the Remove will still follow the principle.   5. For every query and command, decide on a suitable precondition.   We have now focused only on postcondition, now time for some preconditons. The 5th principle is about deciding a suitable preconditon for every query and command. If we starts to look at one of our basic queries (will not go through all Queries and commands here, just some of them) the this[] query, we can’t pass an index that is lower then 1 (.Net arrays and list are zero based, but not the stack in this blog post ;)) and the index can’t be lesser than the number of items in the stack. So here we will need a preconditon. public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Think about the Contract as an documentation about how to use the code in a correct way, so if the contract could be specified elsewhere (not part of the method body), we could simply write “return _array[index]” and there is no need to check if index is greater or lesser than Count, because that is specified in a “contract”. The implementation of Code Contract, requires that the contract is specified in the code. As a developer I would rather have this contract elsewhere (Like Spec#) or implemented in a way Eiffel uses it as part of the language. Now when we have looked at one Query, we can also look at one command, the Remove command (You can see the whole implementation of the Stack at the end of this blog post, where precondition is added to more queries and commands then what I’m going to show in this section). We can only Remove an item if the Count is greater than 0. So we can write a precondition that will require that Count must be greater than 0. public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   6. Write invariants to define unchanging properties of objects.   The last principle is about making sure the object are feeling great! This is done by using invariants. When using Code Contract we can specify invariants by adding a method with the attribute ContractInvariantMethod, the method must be private or public and can only contains calls to Contract.Invariant. To make sure the Stack feels great, the Stack must have 0 or more items, the Count can’t never be a negative value to make sure each command and queries can be used of the Stack. Here is our invariant for the Stack object: [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Note: The ObjectInvariant method will be called every time after a Query or Commands is called. Here is the full example using Code Contract:   public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } set { Contract.Requires(index >= 1); Contract.Requires(index <= Count); _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } //Is related to Count and this[] Query public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } //Creation commands public Stack(uint size) { Contract.Requires(size > 0); Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Requires(value != null); Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } Summary By using Design By Contract we can make sure the users are using our code in a correct way, and we must also make sure the users will get the expected results when they uses our code. This can be done by specifying contracts. To make it easy to use Design By Contract, some principles may be good to follow like the separation of commands an queries. With .Net 4.0 we can use the Code Contract feature to specify contracts.

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  • c++ queue template

    - by Dalton Conley
    ALright, pardon my messy code please. Below is my queue class. #include <iostream> using namespace std; #ifndef QUEUE #define QUEUE /*---------------------------------------------------------------------------- Student Class # Methods # Student() // default constructor Student(string, int) // constructor display() // out puts a student # Data Members # Name // string name Id // int id ----------------------------------------------------------------------------*/ class Student { public: Student() { } Student(string iname, int iid) { name = iname; id = iid; } void display(ostream &out) const { out << "Student Name: " << name << "\tStudent Id: " << id << "\tAddress: " << this << endl; } private: string name; int id; }; // define a typedef of a pointer to a student. typedef Student * StudentPointer; template <typename T> class Queue { public: /*------------------------------------------------------------------------ Queue Default Constructor Preconditions: none Postconditions: assigns default values for front and back to 0 description: constructs a default empty Queue. ------------------------------------------------------------------------*/ Queue() : myFront(0), myBack(0) {} /*------------------------------------------------------------------------ Copy Constructor Preconditions: requres a reference to a value for which you are copying Postconditions: assigns a copy to the parent Queue. description: Copys a queue and assigns it to the parent Queue. ------------------------------------------------------------------------*/ Queue(const T & q) { myFront = myBack = 0; if(!q.empty()) { // copy the first node myFront = myBack = new Node(q.front()); NodePointer qPtr = q.myFront->next; while(qPtr != NULL) { myBack->next = new Node(qPtr->data); myBack = myBack->next; qPtr = qPtr->next; } } } /*------------------------------------------------------------------------ Destructor Preconditions: none Postconditions: deallocates the dynamic memory for the Queue description: deletes the memory stored for a Queue. ------------------------------------------------------------------------*/ ~Queue() { NodePointer prev = myFront, ptr; while(prev != NULL) { ptr = prev->next; delete prev; prev = ptr; } } /*------------------------------------------------------------------------ Empty() Preconditions: none Postconditions: returns a boolean value. description: returns true/false based on if the queue is empty or full. ------------------------------------------------------------------------*/ bool empty() const { return (myFront == NULL); } /*------------------------------------------------------------------------ Enqueue Preconditions: requires a constant reference Postconditions: allocates memory and appends a value at the end of a queue description: ------------------------------------------------------------------------*/ void enqueue(const T & value) { NodePointer newNodePtr = new Node(value); if(empty()) { myFront = myBack = newNodePtr; newNodePtr->next = NULL; } else { myBack->next = newNodePtr; myBack = newNodePtr; newNodePtr->next = NULL; } } /*------------------------------------------------------------------------ Display Preconditions: requires a reference of type ostream Postconditions: returns the ostream value (for chaining) description: outputs the contents of a queue. ------------------------------------------------------------------------*/ void display(ostream & out) const { NodePointer ptr; ptr = myFront; while(ptr != NULL) { out << ptr->data << " "; ptr = ptr->next; } out << endl; } /*------------------------------------------------------------------------ Front Preconditions: none Postconditions: returns a value of type T description: returns the first value in the parent Queue. ------------------------------------------------------------------------*/ T front() const { if ( !empty() ) return (myFront->data); else { cerr << "*** Queue is empty -- returning garbage value ***\n"; T * temp = new(T); T garbage = * temp; delete temp; return garbage; } } /*------------------------------------------------------------------------ Dequeue Preconditions: none Postconditions: removes the first value in a queue ------------------------------------------------------------------------*/ void dequeue() { if ( !empty() ) { NodePointer ptr = myFront; myFront = myFront->next; delete ptr; if(myFront == NULL) myBack = NULL; } else { cerr << "*** Queue is empty -- " "can't remove a value ***\n"; exit(1); } } /*------------------------------------------------------------------------ pverloaded = operator Preconditions: requires a constant reference Postconditions: returns a const type T description: this allows assigning of queues to queues ------------------------------------------------------------------------*/ Queue<T> & operator=(const T &q) { // make sure we arent reassigning ourself // e.g. thisQueue = thisQueue. if(this != &q) { this->~Queue(); if(q.empty()) { myFront = myBack = NULL; } else { myFront = myBack = new Node(q.front()); NodePointer qPtr = q.myFront->next; while(qPtr != NULL) { myBack->next = new Node(qPtr->data); myBack = myBack->next; qPtr = qPtr->next; } } } return *this; } private: class Node { public: T data; Node * next; Node(T value, Node * first = 0) : data(value), next(first) {} }; typedef Node * NodePointer; NodePointer myFront, myBack, queueSize; }; /*------------------------------------------------------------------------ join Preconditions: requires 2 queue values Postconditions: appends queue2 to the end of queue1 description: this function joins 2 queues into 1. ------------------------------------------------------------------------*/ template <typename T> Queue<T> join(Queue<T> q1, Queue<T> q2) { Queue<T> q1Copy(q1), q2Copy(q2); Queue<T> jQueue; while(!q1Copy.empty()) { jQueue.enqueue(q1Copy.front()); q1Copy.dequeue(); } while(!q2Copy.empty()) { jQueue.enqueue(q2Copy.front()); q2Copy.dequeue(); } cout << jQueue << endl; return jQueue; } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a Queue of type T Postconditions: returns the ostream (for chaining) description: this function is overloaded for outputing a queue with << ----------------------------------------------------------------------------*/ template <typename T> ostream & operator<<(ostream &out, Queue<T> &s) { s.display(out); return out; } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a reference of type Student Postconditions: none description: this function is overloaded for outputing an object of type Student. ----------------------------------------------------------------------------*/ ostream & operator<<(ostream &out, Student &s) { s.display(out); } /*---------------------------------------------------------------------------- Overloaded << operator Preconditions: requires a constant reference and a reference of a pointer to a Student object. Postconditions: none description: this function is overloaded for outputing pointers to Students ----------------------------------------------------------------------------*/ ostream & operator<<(ostream &out, StudentPointer &s) { s->display(out); } #endif Now I'm having some issues with it. For one, when I add 0 to a queue and then I output the queue like so.. Queue<double> qdub; qdub.enqueue(0); cout << qdub << endl; That works, it will output 0. But for example, if I modify that queue in any way.. like.. assign it to a different queue.. Queue<double> qdub1; Queue<double> qdub2; qdub1.enqueue(0; qdub2 = qdub1; cout << qdub2 << endl; It will give me weird values for 0 like.. 7.86914e-316. Help on this would be much appreciated!

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  • Why is partial specialziation of a nested class template allowed, while complete isn't?

    - by drhirsch
    template<int x> struct A { template<int y> struct B {};. template<int y, int unused> struct C {}; }; template<int x> template<> struct A<x>::B<x> {}; // error: enclosing class templates are not explicitly specialized template<int x> template<int unused> struct A<x>::C<x, unused> {}; // ok So why is the explicit specialization of a inner, nested class (or function) not allowed, if the outer class isn't specialiced too? Strange enough, I can work around this behaviour if I only partially specialize the inner class with simply adding a dummy template parameter. Makes things uglier and more complex, but it works. Note: I need this feature for recursive templates of the inner class for a set of the outer class. To make things even more complicate, in reality I only need a template function instead of the inner class. But partial specialization of functions is generally disallowed somewhere else in the standard ^^

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  • Template function overloading with identical signatures, why does this work?

    - by user1843978
    Minimal program: #include <stdio.h> #include <type_traits> template<typename S, typename T> int foo(typename T::type s) { return 1; } template<typename S, typename T> int foo(S s) { return 2; } int main(int argc, char* argv[]) { int x = 3; printf("%d\n", foo<int, std::enable_if<true, int>>(x)); return 0; } output: 1 Why doesn't this give a compile error? When the template code is generated, wouldn't the functions int foo(typename T::type search) and int foo(S& search) have the same signature? If you change the template function signatures a little bit, it still works (as I would expect given the example above): template<typename S, typename T> void foo(typename T::type s) { printf("a\n"); } template<typename S, typename T> void foo(S s) { printf("b\n"); } Yet this doesn't and yet the only difference is that one has an int signature and the other is defined by the first template parameter. template<typename T> void foo(typename T::type s) { printf("a\n"); } template<typename T> void foo(int s) { printf("b\n"); } I'm using code similar to this for a project I'm working on and I'm afraid that there's a subtly to the language that I'm not understanding that will cause some undefined behavior in certain cases. I should also mention that it does compile on both Clang and in VS11 so I don't think it's just a compiler bug.

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  • EXSLT date:format-date template without document() XSLT 1.0

    - by DashaLuna
    Hello guys, I'm using date:format-date template EXSLT file I'm using XSLT 1.0 and MSXML3.0 as the processor. My date:format-date template EXSLT file's declaration is: <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:msxsl="urn:schemas-microsoft-com:xslt" xmlns:tui="http://www.travelbound.co.uk/" xmlns:date="http://exslt.org/dates-and-times" exclude-result-prefixes="msxsl tui date" version="1.0"> ... </xsl:stylesheet> I cannot use document() function due to the 3rd party restrictions. So I have changed the months and days (similarly) from XML snippet: <date:months> <date:month length="31" abbr="Jan">January</date:month> <date:month length="28" abbr="Feb">February</date:month> <date:month length="31" abbr="Mar">March</date:month> <date:month length="30" abbr="Apr">April</date:month> <date:month length="31" abbr="May">May</date:month> <date:month length="30" abbr="Jun">June</date:month> <date:month length="31" abbr="Jul">July</date:month> <date:month length="31" abbr="Aug">August</date:month> <date:month length="30" abbr="Sep">September</date:month> <date:month length="31" abbr="Oct">October</date:month> <date:month length="30" abbr="Nov">November</date:month> <date:month length="31" abbr="Dec">December</date:month> </date:months> to the variable: <xsl:variable name="months"> <month length="31" abbr="Jan">January</month> <month length="28" abbr="Feb">February</month> <month length="31" abbr="Mar">March</month> <month length="30" abbr="Apr">April</month> <month length="31" abbr="May">May</month> <month length="30" abbr="Jun">June</month> <month length="31" abbr="Jul">July</month> <month length="31" abbr="Aug">August</month> <month length="30" abbr="Sep">September</month> <month length="31" abbr="Oct">October</month> <month length="30" abbr="Nov">November</month> <month length="31" abbr="Dec">December</month> </xsl:variable> And correspondingly, I've changed the code that originally uses document() function from: [from month processing bit of EXSLT stylesheet] <xsl:variable name="month-node" select="document('')/*/date:months/date:month[number($month)]" /> to use MSXML3.0 node-set function: <xsl:variable name="month-node" select="msxsl:node-set($months)/month[number($month)]" /> So I assumed that this would work. According to the EXLT instructions "The format pattern string is interpreted as described for the JDK 1.1 SimpleDateFormat class." [I used current version]. I'm specifing the month in accordance to SimpleDateFormat class as 'dd MMMMM yyyy' so that the month will be the full month's name, for example January. But it doesn't work :( I've looked in EXSLT stylesheet and it has got the logic to do that. Also there is logic to display the name of the week for a day using 'E' pattern, which doesn't work for me. Maybe changing from using document() to variables broke it. Would really appreciate any help. Many thanks!

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  • Custom Template and Layered Navigation

    - by russjman
    I created a custom template for the category view that displays all subcategories for current category. When i set the current category as is_anchor = yes in the admin, the layered navigation filters show up in the side bar. The Sub categories is one of the filters are there as well, but when i click on one them the page still displays all subcategories. I would like to some how test for active filters in my custom template, which i assume there has to be a way to get this info from Magento. Below is my custom code. $_filters is how i am trying to access these filters, but it gives me nothing. Am i invoking this incorrectly, from the wrong place, in the wrong context? <?php $_helper = $this->helper('catalog/output'); $_filters = $this->getActiveFilters(); echo $_filters; if (!Mage::registry('current_category')) return ?> <?php $_categories=$this->getCurrentChildCategories() ?> <?php $_count = is_array($_categories)?count($_categories):$_categories->count(); ?> <?php if($_count): ?> <?php foreach ($_categories as $_category): ?> <?php if($_category->getIsActive()): ?> <?php $cur_category=Mage::getModel('catalog/category')->load($_category->getId()); $layer = Mage::getSingleton('catalog/layer'); $layer->setCurrentCategory($cur_category); $_imgHtml = ''; if ($_imgUrl = $this->getCurrentCategory()->getImageUrl()) { $_imgHtml = '<img src="'.$_imgUrl.'" alt="'.$this->htmlEscape($_category->getName()).'" title="'.$this->htmlEscape($_category->getName()).'" class="category-image" />'; $_imgHtml = $_helper->categoryAttribute($_category, $_imgHtml, 'image'); } echo $_category->getImageUrl(); ?> <div class="category-image-box"> <div class="category-description clearfix" > <div class="category-description-textbox" > <h2><span><?php echo $this->htmlEscape($_category->getName()) ?></span></h2> <p><?php echo $this->getCurrentCategory()->getDescription() ?></p> </div> <a href="<?php echo $this->getCategoryUrl($_category) ?>" class="collection-link<?php if ($this->isCategoryActive($_category)): ?> active<?php endif ?>" >See Entire Collection</a> <a href="<?php echo $this->getCategoryUrl($_category) ?>"><?php if($_imgUrl): ?><?php echo $_imgHtml ?><?php else: ?><img src="/store/skin/frontend/default/patio_theme/images/category-photo.jpg" class="category-image" alt="collection" /><?php endif; ?></a> </div> <?php echo '<pre>'.print_r($_category->getData()).'</pre>';?> </div> <?php endif; ?> <?php endforeach ?> <?php endif; ?>

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  • Recommended programming language for linux server management and web ui integration

    - by Brendan Martens
    I am interested in making an in house web ui to ease some of the management tasks I face with administrating many servers; think Canonical's Landscape. This means doing things like, applying package updates simultaneously across servers, perhaps installing a custom .deb (I use ubuntu/debian.) Reviewing server logs, executing custom scripts, viewing status information for all my servers. I hope to be able to reuse existing command line tools instead of rewriting the exact same operations in a different language myself. I really want to develop something that allows me to continue managing on the ssh level but offers the power of a web interface for easily applying the same infrastructure wide changes. They should not be mutually exclusive. What are some recommended programming languages to use for doing this kind of development and tying it into a web ui? Why do you recommend the language(s) you do? I am not an experienced programmer, but view this as an opportunity to scratch some of my own itches as well as become a better programmer. I do not care specifically if one language is harder than another, but am more interested in picking the best tools for the job from the beginning. Feel free to recommend any existing projects that already integrate management of many systems into a single cohesive web ui, except Landscape (not free,) Ebox (ebox control center not free) and webmin (I don't like it, feels clunky and does not integrate well with the "debian way" of maintaining a server, imo. Also, only manages one system.) Thanks for any ideas! Update: I am not looking to reinvent the wheel of systems management, I just want to "glue" many preexisting and excellent tools together where possible and appropriate; this is why I wonder about what languages can interact well with pre-existing command line tools, while making them manageable with a web ui.

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  • Does fast typing influence fast programming?

    - by Lukasz Lew
    Many young programmers think that their bottleneck is typing speed. After some experience one realizes that it is not the case, you have to think much more than type. At some point my room-mate forced me to turn of the light (he sleeps during the night). I had to learn to touch type and I experienced an actual improvement in programming skill. The most surprising was that the improvement not due to sheer typing speed, but to a change in mindset. I'm less afraid now to try new things and refactor them later if they work well. It's like having a new tool in the bag. Have anyone of you had similar experience? Now I trained a touch typing a little with KTouch. I find auto-generate lessons the best. I can use this program to create new lessons out of text files but it's only verbatim training, not auto-generated based on a language model. Do you know any touch typing program that allows creation of custom, but randomized lessons?

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  • Pair programming with tmux and Vagrant

    - by neezer
    Does anyone have a clear step-by-step guide for setting up a shared tmux session on a Vagrant vbox that my coworkers (on our local office lan) could SSH into? The articles I've found online only seem to cover setting this up from machine to machine (no virtualbox setups), and I'm not very good at networking, so I haven't been able to extrapolate a solution... We're all running the latest Macs in our office, btw. Here's one article I've found but haven't been able to get working with Vagrant: http://blog.voxdolo.me/remote-pairing-with-vim-and-tmux.html EDIT: To clarify, I don't really know how I should be setting up Vagrant to allow me to SSH into it from a machine outside the one hosting the VM. The article above suggests that I add the tunnels host on my physical machine running the VM (here-on referred to as the MBP), so I did that. Next is the ProxyCommand host declaration, which I have also assumed should live on the MBP. So next I try SSHing into the MBP from a guest machine (another separate physical machine on my network), and that seems to work... but that only gets me into the MBP, not the Vagrant image running on the MBP. I normally login Vagrant image on the MBP via vagrant ssh (per the docs), and I know how to forward ports on the Vagrant VM to the MBP, but it's unclear to me how I could forward ports/SSH from the MBP to the Vagrant VM, which I assume I would need to do so that my guest machine could SSH in--through the MBP--to my Vagrant image. That, in a nutshell, is what I'm trying to accomplish. I do my development work in Vagrant VMs which keeps my MBP nice and clean of any dev-related cruft and also keeps my dev environments totally isolated from one another, yet I would like to start pair-programming with my coworkers via tmux, thus the reason why I've asked this question. I would like to accomplish all of this without setting up an additional user account on the MBP, or giving my coworkers access to my local user account on the MBP to get to my Vagrant VM, if that's at all possible.

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  • No Visual studio template information found. See application log in Event viewer for more details

    - by sathya
    I tried installing the .NET Framework 4.0 and ASP.NET MVC 2 Framework through the web platform installer. It took a long time and finally i had a restart in between for .NET 4 installation and after that due to my system hang problems had to do a couple of restarts. And after that tried installing the ASP.NET MVC 2 alone and it succeeded. (During this time i had all my VS instances closed).  I am having VS 2008 SP1. And finally after opening VS 2008 and clicking on new project it said the above error no template info found. and i dint have even a single template in the new project template selection window. So these are the steps that i did for recovering the same.  Start Menu --> Microsoft Visual Studio 2008 --> Visual Studio Tools. Right-click over the Visual Studio Command Prompt shortcut and make sure you select Run as Administrator. Once the VS Command Prompt comes up, execute the command 1. "devenv /installvstemplates" 2. "devenv /resetsettings"  And that worked out. No Visual studio template information found. See application log in Event viewer for more detail

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  • Missing ideas in programming language design

    - by meyka
    I wanted to try something new and so I designed some programming languages and wrote interpreters for them: A rather low-level, not very expressive language. (I didn't want to parse complex expressions right at the beginning) It featured: Variables (yay) Subroutines, with a call stack Basic arithmetic functions, basic string manipulation, ... Code in the language looks like this: set i 0 inc i print i Very, very basic you see. A more high-level language I decided to make it structured and so it featured things like if-else, while, functions, and so on. The stuff most programming languages have. Ended up like a unworthy Python clone, I hated that. A code-golf language Which ended up similar to J, golfcode, APL, etc. Nothing special As you can see: I don't lack the skills but the ideas. I can't figure out anything new, not even bad, unneccessary things, for my languages. - Do you know of some weird things I could implement in my languages, which don't try to make programming harder (like most esoteric languages) but funnier or more different from other languages? It can't be possible that every weird thing has been tried out so far, or?

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  • How to make a good programming interview?

    - by luckyluke
    I am doing interviews with from time to time to recruit some not bad people. And I really think I AM NOT doing to correct Job. I work in a company when We have to do a lot o DB programming, .NET programming, Java programming, so we need people who are open minded and not focused on a particular tech. Afterall language is a notation, You have to understand what is going under the hood. I ask people about their project, ask them some coding questions (believe me a SQL question involving a CROSS JOIN is hard), let them write some code, ask them about oo design, ask them how they update their knowledge, and stay up to date, do they have FUN when they code (at least sometimes). Hell I even give them a coding solution for home (3 hours max) to see how they think and code. And yet my hit rate at hiring junior member (those who live over the initial 3 months) is just about 33%. So my question, how do YOU make the good interviews, because I think my hit rate is to low? Do you have any best-practices(should be at least 60-70%)? p.s. And i noticed that: the best programmers are lazy, but motivated, just being lazy is not enough:) But people who write the best code are attentive to details:)

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  • What are some programming techniques for converting SD images to HD images

    - by Dr Dork
    I'm taking programming class and instructor loves to work with images so most of our assignments involve manipulating raw RGB image data. One of our assignments is to implement a standard image converter that converts SD images to HD images and vice versa. I always take advantage of these types of assignments to go a little beyond what we were asked to do, so I added a basic anti-aliasing process that uses the average pixel color of the 3x3 surrounding pixels to improve the converted image. While it helps a bit, the resulting image still doesn't look good, which is ok because it's not expected to for the assignment. I've learned that converting an SD to HD images has shown to be much harder than down sampling to SD from HD just because SD to HD effectively involves increasing resolution when it is not there. Obviously, it is hard to create pixels from nothing, but I'd like enhance my anti-aliasing to something that provides better results when upscaling an image. Most of the techniques I find and read on the internet are far beyond my level of image processing and programming. Can anybody suggest any better methods or processes to create good HD content from SD content that may be within my programming skill level? I know that's a difficult thing to gauge since you don't know me, but perhaps knowing that I can write c++ code to read in raw RGB data and upscale/downscale it with simple average-anti-aliasing will give you an idea. Thanks in advance for all your help!

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  • best PHP programming approach?

    - by Nazmin
    Hello guys, i guess that many of us has acceptable years of experience in PHP programming, me myself got 5 years programming in PHP since in University (not very solid), i just want to gather some suggestion here, what is better approach in PHP OOP? Since there is a lot of PHP framework out there as well as javascript framework, can anyone share their experience in using one of them as well as using both of the PHP and javascript framework together especially for developing enterprise system? (my company want to start using framework, ISP company) if someone has his/her own framework or class or php file so on and so forth, mind to share? now I've only database connection class. I've never use any php framework before, just jquery as javascript framework, my company has a messed up of programming approach because they did not actually a software house, so all the files are scattered across the server, I see that there are some question before about the framework but i just want to know you all approaches on OOP and in developing massive web apps using PHP, or maybe someone kind enough to share their solid written class. Also pro's and con's of all this things. Thanks in advance.

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  • career in Mobile sw/Application Development [closed]

    - by pramod
    i m planning to do a course on Wireless & mobile computing.The syllabus are given below.Please check & let me know whether its worth to do.How is the job prospects after that.I m a fresher & from electronic Engg.The modules are- *Wireless and Mobile Computing (WiMC) – Modules* C, C++ Programming and Data Structures 100 Hours C Revision C, C++ programming tools on linux(Vi editor, gdb etc.) OOP concepts Programming constructs Functions Access Specifiers Classes and Objects Overloading Inheritance Polymorphism Templates Data Structures in C++ Arrays, stacks, Queues, Linked Lists( Singly, Doubly, Circular) Trees, Threaded trees, AVL Trees Graphs, Sorting (bubble, Quick, Heap , Merge) System Development Methodology 18 Hours Software life cycle and various life cycle models Project Management Software: A Process Various Phases in s/w Development Risk Analysis and Management Software Quality Assurance Introduction to Coding Standards Software Project Management Testing Strategies and Tactics Project Management and Introduction to Risk Management Java Programming 110 Hours Data Types, Operators and Language Constructs Classes and Objects, Inner Classes and Inheritance Inheritance Interface and Package Exceptions Threads Java.lang Java.util Java.awt Java.io Java.applet Java.swing XML, XSL, DTD Java n/w programming Introduction to servlet Mobile and Wireless Technologies 30 Hours Basics of Wireless Technologies Cellular Communication: Single cell systems, multi-cell systems, frequency reuse, analog cellular systems, digital cellular systems GSM standard: Mobile Station, BTS, BSC, MSC, SMS sever, call processing and protocols CDMA standard: spread spectrum technologies, 2.5G and 3G Systems: HSCSD, GPRS, W-CDMA/UMTS,3GPP and international roaming, Multimedia services CDMA based cellular mobile communication systems Wireless Personal Area Networks: Bluetooth, IEEE 802.11a/b/g standards Mobile Handset Device Interfacing: Data Cables, IrDA, Bluetooth, Touch- Screen Interfacing Wireless Security, Telemetry Java Wireless Programming and Applications Development(J2ME) 100 Hours J2ME Architecture The CLDC and the KVM Tools and Development Process Classification of CLDC Target Devices CLDC Collections API CLDC Streams Model MIDlets MIDlet Lifecycle MIDP Programming MIDP Event Architecture High-Level Event Handling Low-Level Event Handling The CLDC Streams Model The CLDC Networking Package The MIDP Implementation Introduction to WAP, WML Script and XHTML Introduction to Multimedia Messaging Services (MMS) Symbian Programming 60 Hours Symbian OS basics Symbian OS services Symbian OS organization GUI approaches ROM building Debugging Hardware abstraction Base porting Symbian OS reference design porting File systems Overview of Symbian OS Development – DevKits, CustKits and SDKs CodeWarrior Tool Application & UI Development Client Server Framework ECOM STDLIB in Symbian iPhone Programming 80 Hours Introducing iPhone core specifications Understanding iPhone input and output Designing web pages for the iPhone Capturing iPhone events Introducing the webkit CSS transforms transitions and animations Using iUI for web apps Using Canvas for web apps Building web apps with Dashcode Writing Dashcode programs Debugging iPhone web pages SDK programming for web developers An introduction to object-oriented programming Introducing the iPhone OS Using Xcode and Interface builder Programming with the SDK Toolkit OS Concepts & Linux Programming 60 Hours Operating System Concepts What is an OS? Processes Scheduling & Synchronization Memory management Virtual Memory and Paging Linux Architecture Programming in Linux Linux Shell Programming Writing Device Drivers Configuring and Building GNU Cross-tool chain Configuring and Compiling Linux Virtual File System Porting Linux on Target Hardware WinCE.NET and Database Technology 80 Hours Execution Process in .NET Environment Language Interoperability Assemblies Need of C# Operators Namespaces & Assemblies Arrays Preprocessors Delegates and Events Boxing and Unboxing Regular Expression Collections Multithreading Programming Memory Management Exceptions Handling Win Forms Working with database ASP .NET Server Controls and client-side scripts ASP .NET Web Server Controls Validation Controls Principles of database management Need of RDBMS etc Client/Server Computing RDBMS Technologies Codd’s Rules Data Models Normalization Techniques ER Diagrams Data Flow Diagrams Database recovery & backup SQL Android Application 80 Hours Introduction of android Why develop for android Android SDK features Creating android activities Fundamental android UI design Intents, adapters, dialogs Android Technique for saving data Data base in Androids Maps, Geocoding, Location based services Toast, using alarms, Instant messaging Using blue tooth Using Telephony Introducing sensor manager Managing network and wi-fi connection Advanced androids development Linux kernel security Implement AIDL Interface. Project 120 Hours

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  • Where should instantiated classes be stored?

    - by Eric C.
    I'm having a bit of a design dilemma here. I'm writing a library that consists of a bunch of template classes that are designed to be used as a base for creating content. For example: public class Template { public string Name {get; set;} public string Description {get; set;} public string Attribute1 {get; set;} public string Attribute2 {get; set;} public Template() { //constructor } public void DoSomething() { //does something } ... } The problem is, not only is the library providing the templates, it will also supply quite a few predefined templates which are instances of these template classes. The question is, where do I put these instances of the templates? The three solutions I've come up with so far are: 1) Provide serialized instances of the templates as files. On the one hand, this solution would keep the instances separated from the library itself, which is nice, but it would also potentially add complexity for the user. Even if we provided methods for loading/deserializing the files, they'd still have to deal with a bunch of files, and some kind of config file so the app knows where to look for those files. Plus, creating the template files would probably require a separate app, so if the user wanted to stick with the files method of storing templates, we'd have to provide some kind of app for creating the template files. Also, this requires external dependencies for testing the templates in the user's code. 2) Add readonly instances to the template class Example: public class Template { public string Name {get; set;} public string Description {get; set;} public string Attribute1 {get; set;} public string Attribute2 {get; set;} public Template PredefinedTemplate { get { Template templateInstance = new Template(); templateInstance.Name = "Some Name"; templateInstance.Description = "A description"; ... return templateInstance; } } public Template() { //constructor } public void DoSomething() { //does something } ... } This method would be convenient for users, as they would be able to access the predefined templates in code directly, and would be able to unit test code that used them. The drawback here is that the predefined templates pollute the Template type namespace with a bunch of extra stuff. I suppose I could put the predefined templates in a different namespace to get around this drawback. The only other problem with this approach is that I'd have to basically duplicate all the namespaces in the library in the predefined namespace (e.g. Templates.SubTemplates and Predefined.Templates.SubTemplates) which would be a pain, and would also make refactoring more difficult. 3) Make the templates abstract classes and make the predefined templates inherit from those classes. For example: public abstract class Template { public string Name {get; set;} public string Description {get; set;} public string Attribute1 {get; set;} public string Attribute2 {get; set;} public Template() { //constructor } public void DoSomething() { //does something } ... } and public class PredefinedTemplate : Template { public PredefinedTemplate() { this.Name = "Some Name"; this.Description = "A description"; this.Attribute1 = "Some Value"; ... } } This solution is pretty similar to #2, but it ends up creating a lot of classes that don't really do anything (none of our predefined templates are currently overriding behavior), and don't have any methods, so I'm not sure how good a practice this is. Has anyone else had any experience with something like this? Is there a best practice of some kind, or a different/better approach that I haven't thought of? I'm kind of banging my head against a wall trying to figure out the best way to go. Thanks!

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  • iPhone web app from dashcode rss feed template works deployed on simulator but not on iphone

    - by Arge Anton
    iPhone web app from dashcode rss feed template works deployed on simulator but not on iphone. The web app is deployed at; http://www.alila.se/wordpress/index.html If i run the simulator and enter that adress, it fetches the rss feed and displays it. Everything fine. When i enter the adress into my iphone, same os 3.1.2 as the simulator, i just get the header part of the page. No rss feed. The rss feed is; alila.se/wordpress/?feed=rss2 and the source can be downloaded from: alila.se/rss_feed.zip

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  • Django cannot find my templatetags, even though it's in INSTALLED_APPS and has a __init__.py

    - by Vivian Short
    I just installed django-compress (http://code.google.com/p/django-compress) into /Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/site-packages/compress. I added 'compress' to INSTALLED_APPS. In my template file, I wrote {% load compressed %}. I got the error: 'compressed' is not a valid tag library: Could not load template library from django.templatetags.compressed, No module named compressed I verified that there is an init.py in compress, as well as in compress/templatetags/. I tried putting the compress directory into PYTHONPATH. I ran python and wrote "import compress" and that worked. Your suggestions would be very appreciated! What else can I try?

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  • List display names from django models

    - by Ed
    I have an object: POP_CULTURE_TYPES = ( ('SG','Song'), ('MV', 'Movie'), ('GM', 'Game'), ('TV', 'TV'), ) class Pop_Culture(models.Model): name = models.CharField(max_length=30, unique=True) type = models.CharField(max_length=2, choices = POP_CULTURE_TYPES, blank=True, null=True) Then I have a function: def choice_list(request, modelname, field_name): mdlnm = get.model('mdb', modelname.lower()) mdlnm = mdlnm.objects.values_list(field_name, flat=True).distinct().order_by(field_name) return render_to_response("choice_list.html", { 'model' : modelname, 'field' : field_name, 'field_list' : mdlnm }) This gives me a distinct list of all the "type" entries in the database in the "field_list" variable passed in render_to_response. But I don't want a list that shows: SG MV I want a list that shows: Song Movie I can do this on an individual object basis if I was in the template object.get_type_display But how do I get a list of all of the unique "type" entries in the database as their full names for output into a template? I hope this question was clearly described. . .

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  • Good examples of MVVM Template

    - by jwarzech
    I am currently working with the Microsoft MVVM template and find the lack of detailed examples frustrating. The included ContactBook example shows very little Command handling and the only other example I've found is from an MSDN Magazine article where the concepts are similar but uses a slightly different approach and still lack in any complexity. Are there any decent MVVM examples that at least show basic CRUD operations and dialog/content switching? Everyone's suggestions were really useful and I will start compiling a list of good resources Frameworks/Templates WPF Model-View-ViewModel Toolkit MVVM Light Toolkit Prism Caliburn Cinch Useful Articles Data Validation in .NET 3.5 Using a ViewModel to Provide Meaningful Validation Error Messages Action based ViewModel and Model validation Dialogs Command Bindings in MVVM More than just MVC for WPF MVVM + Mediator Example Application Additional Libraries WPF Disciples' improved Mediator Pattern implementation(I highly recommend this for applications that have more complex navigation)

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  • Modification of a template has resulted in confusion...

    - by Dixon Crews
    Hello, I'm working on a site right now that has a short picture slideshow for the homepage. I purchased a template and I am modifying it to work for this situation. On modification, the thumbnail row under the slideshow is now separated from the slideshow and the thumbs are not centered. I can't seem to understand how to get this to get right under the slideshow and have them centered in the row. Any help for me? http://cormanroofinginc.com/ Thanks.

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  • WPF Custom Control - ItemsControl template not being applied.

    - by Patrick White
    I'm building a custom WPF control that derives from TabControl. In the ControlTemplate, I'm using a ItemsControl to display a list that is being bound from the template (an observable collection of type FileMenuItem). During program execution, I'm getting the following error in the output window: ItemTemplate and ItemTemplateSelector are ignored for items already of the ItemsControl's container type; Type='FileMenuItem' The type FileMenuItem is derived from MenuItem. I googled the error and couldn't find anything about it, has anyone run into this while developing custom controls? I can post more code if it would help. Thanks!

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