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  • Write-Through Cache

    - by Mubashar Ahmad
    Dear All I am trying to do an C# implementation of Write-through Cache to minimize the read hits on db i need your suggestions, articles or sample codes to fulfill this assignment. Initially this would be use only on one server but will be updated to work in clustered environment. I only able to get a worth reading article on Oracle Site. Please share your views Regards Mubashar

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  • write system call to file desciptor ZERO

    - by shadyabhi
    int main ( ) { char C[] = "Hello World"; write(0,C,sizeof(C)); return 0; } In the above program, I am writing to File descriptor ZERO which I suppose by default is STDIN.. Then why I am I getting output at STDOUT? shadyabhi@shadyabhi-desktop:~$ ./a.out Hello Worldshadyabhi@shadyabhi-desktop:~$

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  • Read/Write Excel Files Directly To/From Memory

    - by Corey O.
    Several people have asked, in a roundabout way, but I have yet to see a workable solution. Is there any way to open an excel file from directly memory (like a byte[]) ? Likewise is there a way to write a file directly to memory? I am looking for solutions that will not involve the hard disk or juggling temporary files. Thanks in advance for any suggestions.

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  • Need to write at beginning of file with PHP

    - by Timothy
    I'm making this program and I'm trying to find out how to write data to the beginning of a file rather than the end. "a"/append only writes to the end, how can I make it write to the beginning? Because "r+" does it but overwrites the previous data. $datab = fopen('database.txt', "r+"); Here is my whole file: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <title>Facebook v0.1</title> <style type="text/css"> #bod{ margin:0 auto; width:800px; border:solid 2px black; } </style> </head> <body> <div id="bod"> <?php $fname = $_REQUEST['fname']; $lname = $_REQUEST['lname']; $comment = $_REQUEST['comment']; $datab = $_REQUEST['datab']; $gfile = $_REQUEST['gfile']; print <<<form <table border="2" style="margin:0 auto;"> <td> <form method="post" action=""> First Name : <input type ="text" name="fname" value=""> <br> Last Name : <input type ="text" name="lname" value=""> <br> Comment : <input type ="text" name="comment" value=""> <br> <input type ="submit" value="Submit"> </form> </td> </table> form; if((!empty($fname)) && (!empty($lname)) && (!empty($comment))){ $form = <<<come <table border='2' width='300px' style="margin:0 auto;"> <tr> <td> <span style="color:blue; font-weight:bold;"> $fname $lname : </span> $comment </td> </tr> </table> come; $datab = fopen('database.txt', "r+"); fputs($datab, $form); fclose($datab); }else if((empty($fname)) && (empty($lname)) && (empty($comment))){ print" please input data"; } // end table $datab = fopen('database.txt', "r"); while (!feof($datab)){ $gfile = fgets($datab); print "$gfile"; }// end of while ?> </div> </body> </html>

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  • Programs won't write to a file, and I do not know if it is reading it

    - by user320950
    This program is supposed to read files and write them. I took the file open checks out because they kept causing errors. The problem is that the files open like they are supposed to and the names are correct but nothing is on any of the text screens. Do you know what is wrong? #include<iostream> #include<fstream> #include<cstdlib> #include<iomanip> using namespace std; int main() { ifstream in_stream; // reads itemlist.txt ofstream out_stream1; // writes in items.txt ifstream in_stream2; // reads pricelist.txt ofstream out_stream3;// writes in plist.txt ifstream in_stream4;// read recipt.txt ofstream out_stream5;// write display.txt float price=' ',curr_total=0.0; int itemnum=' ', wrong=0; char next; in_stream.open("ITEMLIST.txt", ios::in); // list of avaliable items out_stream1.open("listWititems.txt", ios::out); // list of avaliable items in_stream2.open("PRICELIST.txt", ios::in); out_stream3.open("listWitdollars.txt", ios::out); in_stream4.open("display.txt", ios::in); out_stream5.open("showitems.txt", ios::out); in_stream.close(); // closing files. out_stream1.close(); in_stream2.close(); out_stream3.close(); in_stream4.close(); out_stream5.close(); system("pause"); in_stream.setf(ios::fixed); while(in_stream.eof()) { in_stream >> itemnum; cin.clear(); cin >> next; } out_stream1.setf(ios::fixed); while (out_stream1.eof()) { out_stream1 << itemnum; cin.clear(); cin >> next; } in_stream2.setf(ios::fixed); in_stream2.setf(ios::showpoint); in_stream2.precision(2); while((price== (price*1.00)) && (itemnum == (itemnum*1))) { while (in_stream2 >> itemnum >> price) // gets itemnum and price { while (in_stream2.eof()) // reads file to end of file { in_stream2 >> itemnum; in_stream2 >> price; price++; curr_total= price++; in_stream2 >> curr_total; cin.clear(); // allows more reading cin >> next; } } } out_stream3.setf(ios::fixed); out_stream3.setf(ios::showpoint); out_stream3.precision(2); while((price== (price*1.00)) && (itemnum == (itemnum*1))) { while (out_stream3 << itemnum << price) { while (out_stream3.eof()) // reads file to end of file { out_stream3 << itemnum; out_stream3 << price; price++; curr_total= price++; out_stream3 << curr_total; cin.clear(); // allows more reading cin >> next; } return itemnum, price; } } in_stream4.setf(ios::fixed); in_stream4.setf(ios::showpoint); in_stream4.precision(2); while ( in_stream4.eof()) { in_stream4 >> itemnum >> price >> curr_total; cin.clear(); cin >> next; } out_stream5.setf(ios::fixed); out_stream5.setf(ios::showpoint); out_stream5.precision(2); out_stream5 <<setw(5)<< " itemnum " <<setw(5)<<" price "<<setw(5)<<" curr_total " <<endl; // sends items and prices to receipt.txt out_stream5 << setw(5) << itemnum << setw(5) <<price << setw(5)<< curr_total; // sends items and prices to receipt.txt out_stream5 << " You have a total of " << wrong++ << " errors " << endl; }

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  • FileNotFound exception when trying to write to a file

    - by Chris Knight
    OK, I'm feeling like this should be easy but am obviously missing something fundamental to file writing in Java. I have this: File someFile = new File("someDirA/someDirB/someDirC/filename.txt"); and I just want to write to the file. However, while someDirA exists, someDirB (and therefore someDirC and filename.txt) do not exist. Doing this: BufferedWriter writer = new BufferedWriter(new FileWriter(someFile)); throws a FileNotFoundException. Well, er, no kidding. I'm trying to create it after all. Do I need to break up the file path into components, create the directories and then create the file before instantiating the FileWriter object?

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  • How to write to the OpenGL Depth Buffer

    - by Mikepote
    I'm trying to implement an old-school technique where a rendered background image AND preset depth information is used to occlude other objects in the scene. So for instance if you have a picture of a room with some wires hanging from the ceiling in the foreground, these are given a shallow depth value in the depthmap, and when rendered correctly, allows the character to walk "behind" the wires but in front of other objects in the room. So far I've tried creating a depth texture using: glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, Image.GetWidth(), Image.GetHeight(), 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, pixels); Then just binding it to a quad and rendering that over the screen, but it doesnt write the depth values from the texture. I've also tried: glDrawPixels(Image.GetWidth(), Image.GetHeight(), GL_DEPTH_COMPONENT, GL_UNSIGNED_BYTE, pixels); But this slows down my framerate to about 0.25 fps... I know that you can do this in a pixelshader by setting the gl_fragDepth to a value from the texture, but I wanted to know if I could achieve this with non-pixelshader enabled hardware?

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  • using bash: write bit representation of integer to file

    - by theseion
    Hullo First, I want to use bash for this and the script should run on as many systems as possible (I don't know if the target system will have python or whatever installed). Here's the problem: I have a file with binary data and I need to replace a few bytes in a certain position. I've come up with the following to direct bash to the offset and show me that it found the place I want: dd bs=1 if=file iseek=24 conv=block cbs=2 | hexdump Now, to use "file" as the output: echo anInteger | dd bs=1 of=hextest.txt oseek=24 conv=block cbs=2 This seems to work just fine, I can review the changes made in a hex editor. Problem is, "anInteger" will be written as the ASCII representation of that integer (which makes sense) but I need to write the binary representation. How do I tell the command to convert the input to binary (possibly from a hex)?

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  • Limit of 88 bytes on response.write?

    - by Chris
    I am trying to serve a csv file from a wcf service, as a string response. It looks like this: HttpContext.Current.Response.AddHeader("Content-disposition", "attachment; filename=ImportErrors.csv"); HttpContext.Current.Response.ContentType = "text/csv"; HttpContext.Current.Response.Write(myCsvContent); The response StatusCode is set to (int)HttpStatusCode.OK (200) It works, but I am only getting 88 bytes of my csv and the rest is cut off (not shown). Any suggestions on where to look? I don't see any custom entries in my web.config that are setting a limit.

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  • document.write Javascript error [ SOLVED]

    - by DevMobile
    Now I'm getting the following error: ';'expected document.write("<script type='text/javascript'>var twitterwind_option = {'isOnlyMe':true,'twitterwind_logo':'','twitterwind_logo_bgcolor':'FFFFFF','twitterwind_logo_color':'333303','followers_color':'000000','followers_bgcolor':'FFFFFF','twitterwind_max_length':'39','twitterwind_username':'table-row','twitterwind_username_color':'333333','twitterwind_username_bgcolor':'FFFFFF','twitterwind_twit':'block','twitterwind_twit_color':'333333','twitterwind_twit_bgcolor':'FFFFFF','twitterwind_twit_link_color':'0084B4','twitterwind_twit_scroll_color':'C0DEED','twitterwind_twit_scroll_bg_color':'FFFFFF','twitterwind_follower':'inherit','twitterwind_follower_bgcolor':'FFFFFF','twitterwind_frame_width':200,'twitterwind_frame_height':480,'twitterwind_frame_border':'false','twitterwind_frame_border_color':'C0DEED','twitterwind_base_font_size':12,'twitterwind_me_font_size':14,'twitterwind_caption_font_size':16,'twitterwind_scroll_height':336,'eusn':'rdK1y36H5sM='}';var twitterwind_url = 'http://www.tweetswind.com/en/twitterwind.php';<\/script><script type='text/javascript' src='http://www.tweetswind.com/en/js/twitterwind.js'><\/script><div style='font-size:12px; text-align:right; width:200px'><a target='_blank' href='http://www.tweetswind.com/en/en/'>TweetsWind: a Twitter widget</a></div>");src='http://www.tweetswind.com/en/js/twitterwind.js'></script><div style='font-size:12px; text-align:right; width:200px'><a target='_blank' href='http://www.tweetswind.com/en/en/'>TweetsWind: a Twitter widget</a></div>");

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  • Write set of integers to std::ofstream and be able to read them back

    - by bndu
    Hello, I need to write a bunch of unsigned integers to std::ofstream in binary mode: std::ofstream f; f.open("some path", std::ios::out | std::ios::binary); // some loop { unsigned int k = get_k(); // may product numbers from 0 to 65535 f << k; } f.close(); They are written to the output file "as is" w/o any delimiter. So when I'm trying to read them back (expecting to get what I wrote) using std::ifstream I get very strange values. What I'm doing wrong? Or I should to put ' ' (space) to the stream after any added number to separate them? Thanks.

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  • Write XML using best way(Linq To XML or other)

    - by Pankaj
    Hello All I want to write my xml with following format. How can i do it?I am using c# <map borderColor='c5e5b8' fillColor='6a9057' numberSuffix=' Mill.' includeValueInLabels='0' labelSepChar=': ' baseFontSize='9' showFCMenuItem='0' hoverColor='c2bc23' showTitle='0' type='0' showCanvasBorder='0' bgAlpha='0,0' hoveronEmpty='1' includeNameInLabels='0' showLabels='1'> <!--toolText='Alaska'imageSave='1' imageSaveURL='Path/FusionChartsSave.aspx or FusionChartsSave.php'--> <data> <entity id='AL' value='AL' link="JavaScript:FilterClientProjectList('AL');" fontBold='1' showLabel='0' /> <entity id='AK' value='AK' link="JavaScript:FilterClientProjectList('AK');" fontBold='1' hoverColor='6a9057'/> <entity id='AZ' value='AZ' link="JavaScript:FilterClientProjectList('AZ');" fontBold='1'/> </data> <styles> <definition> <style name='MyFirstFontStyle' type='font' face='Verdana' size='11' color='0372AB' bold='1' bgColor='FFFFFF' /> </definition> <application> <apply toObject='Labels' styles='' /> </application> </styles> </map> Thanks in advance..

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  • C++ Serial Port Only Responding Once Using Write()

    - by Pfeffer
    All the code below works. My device responds, C,7 is a reset. When I run this the second time it doesn't respond. If I manually turn my device off and on, then run this script again it works. But not if I press the button to run the script the second time. RS232: 57600,8,N,1 Any ideas?? Is there any more information needed to solve this? *Also when I get this working I'm going to have to use the read() function to get the devices responses. Does anyone know the correct format I need to use, based on the below code? Sorry I'm new to C++...I'm more of a PHP guy. *I also don't know if 1024 is right, but it seems to work so eh... Thanks so much! #include <termios.h> int fd; struct termios options; fd=open("/dev/tty.KeySerial1", O_RDWR | O_NOCTTY | O_NDELAY); fcntl(fd, F_SETFL, 0); tcgetattr(fd,&options); options.c_ispeed=57600; options.c_ospeed=57600; options.c_cflag |= (CLOCAL | CREAD); options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG); options.c_cflag &= ~CSTOPB; options.c_lflag &= ~ECHO; options.c_oflag &= ~ECHO; options.c_oflag &= ~OPOST; options.c_cflag |= CS8; options.c_cflag |= CRTSCTS; options.c_cc[VMIN] = 0; options.c_cc[VTIME] =10; tcflush(fd, TCIFLUSH); tcsetattr(fd,TCSANOW,&options); write(fd, "C,7\r\n", 1024); close(fd);

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  • WordPress Write Cache Problem with Multiple Sessions

    - by Volomike
    I'm working on a content dripper custom plugin in WordPress that my client asked me to build. He says he wants it to catch a page view event, and if it's the right time of day (24 hours since last post), to pull from a resource file and output another post. He needed it to also raise a flag and prevent other sessions from firing that same snippet of code. So, raise some kind of flag saying, "I'm posting that post, go away other process," and then it makes that post and releases the flag again. However, the strangest thing is occurring when placed under load with multiple sessions hitting the site with page views. It's firing instead of one post -- it's randomly doing like 1, 2, or 3 extra posts, with each one thinking that it was the right time to post because it was 24 hours past the time of the last post. Because it's somewhat random, I'm guessing that the problem is some kind of write caching where the other sessions don't see the raised flag just yet until a couple microseconds pass. The plugin was raising the "flag" by simply writing to the wp_options table with the update_option() API in WordPress. The other user sessions were supposed to read that value with get_option() and see the flag, and then not run that piece of code that creates the post because a given session was already doing it. Then, when done, I lower the flag and the other sessions continue as normal. But what it's doing is letting those other sessions in. To make this work, I was using add_action('loop_start','checkToAddContent'). The odd thing about that function though is that it's called more than once on a page, and in fact some plugins may call it. I don't know if there's a better event to hook. Even still, even if I find an event to hook that only runs once on a page view, I still have multiple sessions to contend with (different users who may view the page at the same time) and I want only one given session to trigger the content post when the post is due on the schedule. I'm wondering if there are any WordPress plugin devs out there who could suggest another event hook to latch on to, and to figure out another way to raise a flag that all sessions would see. I mean, I could use the shared memory API in PHP, but many hosting plans have that disabled. Can't use a cookie or session var because that's only one single session. About the only thing that might work across hosting plans would be to drop a file as a flag, instead. If the file is present, then one session has the flag. If the file is not present, then other sessions can attempt to get the flag. Sure, I could use the file route, but it's kind of immature in my opinion and I was wondering if there's something in WordPress I could do.

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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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  • Demo on Data Guard Protection From Lost-Write Corruption

    - by Rene Kundersma
    Today I received the news a new demo has been made available on OTN for Data Guard protection from lost-write corruption. Since this is a typical MAA solution and a very nice demo I decided to mention this great feature also in this blog even while it's a recommended best practice for some time. When lost writes occur an I/O subsystem acknowledges the completion of the block write even though the write I/O did not occur in the persistent storage. On a subsequent block read on the primary database, the I/O subsystem returns the stale version of the data block, which might be used to update other blocks of the database, thereby corrupting it.  Lost writes can occur after an OS or storage device driver failure, faulty host bus adapters, disk controller failures and volume manager errors. In the demo a data block lost write occurs when an I/O subsystem acknowledges the completion of the block write, while in fact the write did not occur in the persistent storage. When a primary database lost write corruption is detected by a Data Guard physical standby database, Redo Apply (MRP) will stop and the standby will signal an ORA-752 error to explicitly indicate a primary lost write has occurred (preventing corruption from spreading to the standby database). Links: MOS (1302539.1). "Best Practices for Corruption Detection, Prevention, and Automatic Repair - in a Data Guard Configuration" Demo MAA Best Practices Rene Kundersma

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  • iPhone: How to write plist array of dictionary object

    - by Alessandro
    Hello, I'm a young Italian developer for the iPhone. I have a plist file (named "Frase") with this structure: Root Array - Item 0 Dictionary Frase String Preferito Bool - Item 1 Dictionary Frase String Preferito Bool - Item 2 Dictionary Frase String Preferito Bool - Item 3 Dictionary Frase String Preferito Bool exc. An array that contains many elements dictionary, all the same, consisting of "Frase" (string) and "Preferito" (BOOL). The variable "indirizzo", increase or decrease the click of the button Next or Back. The application interface: http://img691.imageshack.us/img691/357/schermata20100418a20331.png When I click on AddPreferito button, the item "Preferito" must be YES. Subsequently, the array must be updated with the new dictionary.The code: (void)addpreferito:(id)sender { NSString *plistPath = [[NSBundle mainBundle] pathForResource:@"Frase" ofType:@"plist"]; MSMutableArray *frase = [[NSMutableArray alloc] initWithContentsOfFile:plistPath]; NSMutableDictionary *dictionary = [frase objectAtIndex:indirizzo]; [dictionary setValue: YES forKey:@"Preferito"]; [frase replaceObjectAtIndex:indirizzo withObject:dictionary]; [frase writeToFile:plistPath atomically:YES]; } Why not work? Thanks Thanks Thanks!

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  • Mirror SVN Repository [Write-through proxying]

    - by Munim Abdul
    Hi, I have a codebase located in Europe and access this codebase from Asia. Codebase is substantially huge, downloading the whole codebase (which is required sometimes) becomes a pain. I wanted to know whether anything like this. I want a solution that "I will have a svn server locally which will sync with the main svn and serve my team as the svn is locally hosted." Thanks in advance Munim

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  • Fedora12 Slow USB 2.0 Write Speed, ehci_hcd module is missing.

    - by MA1
    I am using Fedora 12, the problem i am facing is USB 2.0 write speed. I have a dual boot system with Window XP and Fedora 12. USB 2.0 write speed in Windows XP is much faster then what i am getting in Fedora 12. After some googling i came to know that ehci_hcd module is missing/not present in my system. ehci_hcd module is neither loaded nor it is present in the available list of modules. Can someone guide me how to fix this issue? Is ehci_hcd have something to do with USB 2.0 write speed or? Should i have to recompile the kernel and add/enable he ehci_hcd module?

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  • Cocoa: Using UNIX based commands to write a file

    - by BryCry
    I'm looking for help with a program im making. I create a *.sh file as follows: SVN_StatGenAppDelegate.h: NSWindow *window; NSTask *touch; NSArray *touchArguments; NSString *svnURLStr; NSString *SVNStatStr; NSString *destDirStr; SVN_StatGenApplDelegate.m: NSString *locationStr = [NSString stringWithFormat:@"%@/exec.sh", destDirStr]; NSLog(@"%@", locationStr); touch = [[NSTask alloc] init]; [touch setLaunchPath:@"/usr/bin/touch"]; touchArguments = [NSArray arrayWithObjects:locationStr, nil]; [touch setArguments:touchArguments]; [touch launch]; This works, i get a file called exec.sh created in the location i craete with the destDirStr. Now is my next question, i need to get that file filled with the following: svn co http://repo.com/svn/test C:\users\twan\desktop\pres\_temp cd C:\users\twan\desktop\pres\_temp svn log -v --xml > logfile.log copy C:\users\twan\desktop\statsvn.jar C:\users\twan\desktop\pres\_temp cd .. java -jar _temp\statsvn.jar C:\users\twan\desktop\pres\_temp/logfile.log C:\users\twan\desktop\pres\_temp rmdir /s /Q _temp The actual idea is that this script is written into the sh file, and all the _temp and other locations are replaced by the vars i get from textfields etc. so c:\users\twan\desktop\pres_temp would be a var called tempDirStr that i get from my inputfields. (i know these cmomands and locations are windows based, im doing this with a friend and he made a .net counterpart of the application. Can you guys help me out?:D thanks in advance!

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  • Write/read count to txt file

    - by Brian
    Hi, I need a batch file that writes the count number to a txt file. Next time the batch file is run, it should read the current count number from the txt file and add 1 to count and save this new value in the txt file. (nothing else is in the txt file) When count is 5 it should start from 1 again Example: Count.bat runs 1 time: count.txt has no count so Count.bat saves the value 1 in count.txt Count.bat is run 2 time: Count.bat reads 1 from count.txt and saves the new value 2 to count.txt When count.bat is run for the 6 time it should start over by saving the value 1 in count.txt I think this just be easy to do, but I'am not use to batch commands So hopefully someone here could help me.

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  • How to group a database write and spreadsheet write in single "transaction"

    - by WhyGeeEx
    I have a Java program that writes results to both a DB (SQL Server) and a spreadsheet (POI), and it would be best if neither is written to if there's an error with either. It would be a lot worse if the spreadsheet was produced and then an error happened while saving to the DB, so I'm doing the DB-write first. Even so, I'm wondering if someone knows of a way to guarantee they both succeed or fail as a unit. Thanks!

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  • Why Response.Write behavior varies in the given scenario?

    - by Sri Kumar
    Hello All, When i POST the page using the following code, the Response.write("Hey") doesn't write the content ("Hello") to the parent page <form method="post" name="upload" enctype="multipart/form-data" action="http://localhost:2518/Web/CrossPage.aspx?cmd=getvalue" > <input type="file" name="filename" /> <input type="submit" value="Upload Data File" name="cmdSubmit" /> </form> But When i use following code , and POST the data, the Response.write("Hey") can be obtained in the parent page HttpWebRequest requestToSender = (HttpWebRequest)WebRequest.Create("http://localhost:2518/Web/CrossPage.aspx?cmd=getvalue"); requestToSender.Method = "POST"; requestToSender.ContentType = "multipart/form-data"; HttpWebResponse responseFromSender = (HttpWebResponse)requestToSender.GetResponse(); string fromSender = string.Empty; using (StreamReader responseReader = new StreamReader(responseFromSender.GetResponseStream())) { fromSender = responseReader.ReadToEnd(); } In the CrossPage.aspx i have the following code if (!Page.IsPostBack) { NameValueCollection postPageCollection = Request.Form; foreach (string name in postPageCollection.AllKeys) { Response.Write(name + " " + postPageCollection[name]); } HttpFileCollection postCollection = Request.Files; foreach (string name in postCollection.AllKeys) { HttpPostedFile aFile = postCollection[name]; aFile.SaveAs(Server.MapPath(".") + "/" + Path.GetFileName(aFile.FileName)); } Response.Write("Hey"); } I don't have any code in the Page_Load event of parent page.? What could be the cause? I need to write the "hey" to the Parent page using the first scenario. Both the application are of different domain. Edit: "Hey" would be from the CrossPage.aspx. I need to write this back to the Parent Page

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