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  • LEMP Stack on Ubuntu Server 13.04 not parsing PHP Switch Statement Properly

    - by schester
    On my Ubuntu 12.04 Server LTS on nginx 1.1.19, the following PHP code works properly: switch($_SESSION['user']['permissions']) { case 9: echo "Super Admin Privileges"; break; case 0: echo "Operator Privileges"; break; case 1: echo "Line Leader Privileges"; break; case 2: echo "Supervisor Privileges"; break; case 3: echo "Engineer Privileges"; break; case 4: echo "Manager Privileges"; break; case 5: echo "Administrator Privileges"; break; default: echo "Operator Privileges"; } However, I have a backup server running Ubuntu Server 13.04 on nginx 1.4.1 which has the exact same copy of the script (synced) but instead of breaking on the break; command, it echos the whole php script. The output on the 12.04 Box is similar to this: You are logged in with Super Admin Privileges But on the 13.04 Box, the output is like this: You are logged in logged in with Super Admin Privileges"; break; case 0: echo "Operator Privileges"; break; case 1: echo "Line Leader Privileges"; break; case 2: echo "Supervisor Privileges"; break; case 3: echo "Engineer Privileges"; break; case 4: echo "Manager Privileges"; break; case 5: echo "Administrator Privileges"; break; default: echo "Operator Privileges"; } ?> I have also tried changing the script from switch statement to if statements but same results. Any idea what is wrong?

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  • the web technology stack is too deep [closed]

    - by AgostinoX
    A standard state-of-the-art project requires at least jsf + spring + faces palette + orm. That's a lot of stuff. Also frameworks like spring misses to bring to the point of starting developing. Otherwise, things like spring-roo wuoldn't even exist. The solution to this may be buy support. Have dedicated people doing integration. Switch to ruby on rails. Switch to dot.net. Since this is a problem, I'm intrested in HOW people address this (java ee) specific concern.

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  • The Simplicity of the Oracle Stack

    - by user801960
    For many retailers, technology is something they know they need to optimise business operations, but do they really understand it and how can they select the solutions they need from the many vendors on the market? Retail is a data heavy industry, with the average retailer managing thousands of SKUs and hundreds of categories through multiple channels. Add to this the exponential growth in data driven by social media and mobile activities, and the process can seem overwhelming. Handling data of this magnitude and analyzing it effectively to gain actionable insight is a huge task, and needs several IT components to work together harmoniously to make the best use of the data available and make smarter decisions. With this in mind, Oracle has produced a video to make it easier for businesses to understand its global data IT solutions and how they integrate seamlessly with Oracle’s other solutions to enable organisations to operate as effectively as possible. The video uses an orchestra as an analogy for IT solutions and clever illustration to demonstrate the value of the Oracle brand. This video can be viewed at http://medianetwork.oracle.com/video/player/1622148401001. To find out more about how Oracle’s products and services can help retailers to deliver better results, visit the Oracle Retail website.

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  • The C++ web stack, is there one?

    - by NimChimpsky
    Java would be jsps and servlets (or a framework such as Spring) running on the JVM and tomcat (or glassfish etc). C# would be asp and C# running on dot.net framework and IIS ? (I have no experience with this please correct and improve my terminology) Is there an equivalent for C++ ? I could happily call some C++ from a java servlet/controller but was wondering if there are existing frameworks and libraries out there specifically for creating business logic in C++ with a web front end.

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  • vagrant fails to bring up additional adapter for centos vm using virtual box provider

    - by Anadi Misra
    this is in continuation of the question asked here about host only adapter on dhcp I upgraded to vagrant 1.6.3 and the updated Vagrantfile to following setting for multiple adapters # add additional adapter for inter machine networking dev.vm.network :private_network, :type => "dhcp", :adapter => "2", :netmask => "255.255.255.0" it goes through creating adapters but then fails bringing up the mic on vm Anadis-MacBook-Pro:full-stack-env anadi$ vagrant up Bringing machine 'full-stack-env' up with 'virtualbox' provider... ==> full-stack-env: Clearing any previously set forwarded ports... ==> full-stack-env: Clearing any previously set network interfaces... ==> full-stack-env: Preparing network interfaces based on configuration... full-stack-env: Adapter 1: nat full-stack-env: Adapter 2: hostonly ==> full-stack-env: Forwarding ports... full-stack-env: 22 => 4223 (adapter 1) full-stack-env: 8080 => 8090 (adapter 1) ==> full-stack-env: Running 'pre-boot' VM customizations... ==> full-stack-env: Booting VM... ==> full-stack-env: Waiting for machine to boot. This may take a few minutes... full-stack-env: SSH address: 127.0.0.1:4223 full-stack-env: SSH username: vagrant full-stack-env: SSH auth method: private key full-stack-env: Warning: Connection timeout. Retrying... full-stack-env: Warning: Connection timeout. Retrying... full-stack-env: Warning: Remote connection disconnect. Retrying... ==> full-stack-env: Machine booted and ready! ==> full-stack-env: Checking for guest additions in VM... ==> full-stack-env: Setting hostname... ==> full-stack-env: Configuring and enabling network interfaces... The following SSH command responded with a non-zero exit status. Vagrant assumes that this means the command failed! ARPCHECK=no /sbin/ifup eth 2> /dev/null Stdout from the command: Device eth does not seem to be present, delaying initialization. Stderr from the command: how ever when I log in to the environment I see two network interfaces as expected Anadis-MacBook-Pro:full-stack-env anadi$ vagrant ssh Last login: Wed Jun 4 12:54:47 2014 from 10.0.2.2 [[email protected] ~]$ ifconfig eth0 Link encap:Ethernet HWaddr 08:00:27:BD:39:57 inet addr:10.0.2.15 Bcast:10.0.2.255 Mask:255.255.255.0 inet6 addr: fe80::a00:27ff:febd:3957/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:511 errors:0 dropped:0 overruns:0 frame:0 TX packets:360 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:54574 (53.2 KiB) TX bytes:46675 (45.5 KiB) eth1 Link encap:Ethernet HWaddr 08:00:27:A3:86:C9 inet addr:172.28.128.3 Bcast:172.28.128.255 Mask:255.255.255.0 inet6 addr: fe80::a00:27ff:fea3:86c9/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:5 errors:0 dropped:0 overruns:0 frame:0 TX packets:9 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:1360 (1.3 KiB) TX bytes:894 (894.0 b) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:0 (0.0 b) TX bytes:0 (0.0 b) I am bit confused here on why it is trying to add another mic (eth2)? In the VM I used for creating this vagrant box, I had added two NICs already.

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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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  • x86_64 Assembly Command Line Arguments

    - by Brandon oubiub
    I'm new to assembly, and I just got familiar with the call stack, so bare with me. To get the command line arguments in x86_64 on Mac OS X, I can do the following: _main: sub rsp, 8 ; 16 bit stack alignment mov rax, 0 mov rdi, format mov rsi, [rsp + 32] call _printf Where format is "%s". rsi gets set to argv[0]. So, from this, I drew out what (I think) the stack looks like initially: top of stack <- rsp after alignment return address <- rsp at beginning (aligned rsp + 8) [something] <- rsp + 16 argc <- rsp + 24 argv[0] <- rsp + 32 argv[1] <- rsp + 40 ... ... bottom of stack And so on. Sorry if that's hard to read. I'm wondering what [something] is. After a few tests, I find that it is usually just 0. However, occasionally, it is some (seemingly) random number. EDIT: Also, could you tell me if the rest of my stack drawing is correct?

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  • Stack overflow while working with CFBuilder plugin

    - by lynxoid
    In the past 30 minutes of working in CFBuilder (I have it as an Eclipse Plug in), I got this error 4 times: A stack overflow has occurred. You are recommended to exit the workbench. Subsequent errors may happen and may terminate the workbench without warning. See the .log file for more details. Do you want to exit workbench?. together with: Unhandled event loop exception java.lang.StackOverflowError The log file had this: !ENTRY org.eclipse.ui 4 0 2010-05-11 09:41:51.951 !MESSAGE Unhandled event loop exception !STACK 0 java.lang.StackOverflowError at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.sort(Unknown Source) at com.adobe.ide.cfml.parser.generated.CFMLParserBase.getVariableInfo(CFMLParserBase.java:1613) at com.adobe.ide.cfml.parser.generated.CFMLParserBase.getVariableInfo(CFMLParserBase.java:1603) at com.adobe.ide.editor.model.CFMLDOMUtils.getVariable(CFMLDOMUtils.java:2375) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromNode(CFMLDOMUtils.java:2484) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromFunctionCall(CFMLDOMUtils.java:2168) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromNode(CFMLDOMUtils.java:2495) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromFunctionCall(CFMLDOMUtils.java:2168) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromNode(CFMLDOMUtils.java:2495) at com.adobe.ide.editor.model.CFMLDOMUtils.getComponentNameFromFunctionCall(CFMLDOMUtils.java:2168) (and so on - repeat n times) It happens whenever I copy/paste something. Does anyone know what is going on?

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  • Download all Stack Overflow podcasts onto my iPhone

    - by Casebash
    I want to copy all of the Stack Overflow podcasts onto my iPhone. Unfortunately, iTunes will only let me get the last 10. Nik suggested a method of importing MP3s into iTunes, but it appears that this would make them appear in the music section rather than the podcast section. Is there any way to easily do this?

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  • Complete stack traces from Hyperic

    - by Mike Kushner
    I've setup Hyperic to run on our CI-machine, and every once in a while it reacts to some random stack trace and sends of an alert. So far so good, we've caught a lot of intermittent bugs that way. My only issue is that the alert only contains the first error line and not the entire stack trace, which requires me to access the machine and look at the logs manually. Is there any way to modify the alert message to contain more information, alternatively to include the log file in the alert mail?

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  • Jquery history, inspect the history stack

    - by nickmorss
    Im using this history jquery plugin http://www.mikage.to/jquery/jquery_history.html and im trying to inspect the back stack. I can call this $.historyCurrentHash to return the current hash, but im trying to figure out how to look one step back in the stack. if i try calling this $.historyBackStack, but i just get an 'undefined'. anyone got any ideas? I can see that its not a public variable, but im wondering if i need to modify the library or just call it in a different way

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  • Fill CSS box with text from MySQL till there is no overflow, scrollbar, or hidden text

    - by terrance branigan
    I want to fill a CSS box with text till there is no overflow or scrollbar. I fetch text from MySQL. The user clicks a button and the next bit of text that can fit will fill the box. The only way I've figured to do this is by parsing through the text and counting characters and newlines, etc and calculating whether it will fit in the box. Is there an easier way to do this? Thank you

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  • Stack Trace of cross-thread exceptions with Invoke

    - by the_lotus
    When an exception happens after calling Invoke, .NET shows the stack trace as if the error happens while calling Invoke. Example below: .NET will say the error happen in UpdateStuff instead of UpdateStuff - BadFunction Is there a way to catch the "real" exception and show the correct stack trace? Private Sub UpdateStuff() If (Me.InvokeRequired) Then Me.Invoke(New UpdateStuffDelegate(AddressOf UpdateStuff)) Return End If Badfunction() End Sub Private Sub BadFunction() Dim o As Object o.ToString() End Sub

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  • Anticipate factorial overflow

    - by Flavius
    Hi I'm wondering how I could anticipate that the next iteration will generate an integer overflow while calculating the factorial F. Let's say that at each iteration I have an int I and the maximum value is MAX_INT. It sounds like a homework, I know. It's not. It's just me asking myself "stupid" questions.

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  • increase stack size

    - by PMC
    Hi there, I am working with scons and am trying to compile a program that require bigger stack size but I dont know how to extend the stack size. This is on a solaris machine, and as I said before, we use scons to compile our projects. Anyone know how to do this ?

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  • Good programming website like Stack Overflow?

    - by hhafez
    What other good collaborative programming/software development/engineering websites do you know of? I'm not looking for language or platform specific websites. Nor am I looking for something similar to the format of Stack Overflow. My main criteria is that the community is knowledgeable, helpful active friendly I know the question is open ended/subjective but I'd like to know as many places where I can get the help of my peers. The accepted answer will contain links to your recommended sites have a short description be concise be highly voted by your peers

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  • Capturing the overflow:auto state of a div

    - by jerrygarciuh
    Hi folks, One of the ad agencies I code for had me set up an alternate scrolling solution because you know how designers hate things that just work but aren't beautiful. So, this is married in places to their CMS. What I have not been able to sort yet is how to hide the scrolling UI when overflow:auto is not triggered by the CMS content. Any ideas? TIA JG

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  • Stack and queue operations on the same array.

    - by Passonate Learner
    Hi. I've been thinking about a program logic, but I cannot draw a conclusion to my problem. Here, I've implemented stack and queue operations to a fixed array. int A[1000]; int size=1000; int top; int front; int rear; bool StackIsEmpty() { return (top==0); } bool StackPush( int x ) { if ( top >= size ) return false; A[top++] = x; return true; } int StackTop( ) { return A[top-1]; } bool StackPop() { if ( top <= 0 ) return false; A[--top] = 0; return true; } bool QueueIsEmpty() { return (front==rear); } bool QueuePush( int x ) { if ( rear >= size ) return false; A[rear++] = x; return true; } int QueueFront( ) { return A[front]; } bool QueuePop() { if ( front >= rear ) return false; A[front++] = 0; return true; } It is presumed(or obvious) that the bottom of the stack and the front of the queue is pointing at the same location, and vice versa(top of the stack points the same location as rear of the queue). For example, integer 1 and 2 is inside an array in order of writing. And if I call StackPop(), the integer 2 will be popped out, and if I call QueuePop(), the integer 1 will be popped out. My problem is that I don't know what happens if I do both stack and queue operations on the same array. The example above is easy to work out, because there are only two values involved. But what if there are more than 2 values involved? For example, if I call StackPush(1); QueuePush(2); QueuePush(4); StackPop(); StackPush(5); QueuePop(); what values will be returned in the order of bottom(front) from the final array? I know that if I code a program, I would receive a quick answer. But the reason I'm asking this is because I want to hear a logical explanations from a human being, not a computer.

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