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• Java Web App: Passing form parameters across multiple pages

  - by digiarnie

  Hi, what is the best practice or best way of passing form parameters from page to page in a flow? If I have a flow where a user enters data in a form and hits next and repeats this process until they get to an approval page, what ways could I approach this problem to make the retention of data as simple as possible over the flow? I guess you could put all the information as you go in the session but could you get into memory issues if a lot of people are using your app and going through the flow at the same time?

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• Homemade fstat to get file size, always return 0 length.

  - by Fred

  Hello, I am trying to use my own function to get the file size from a file. I'll use this to allocate memory for a data structure to hold the information on the file. The file size function looks like this: long fileSize(FILE *fp){ long start; fflush(fp); rewind(fp); start = ftell(fp); return (fseek(fp, 0L, SEEK_END) - start); } Any ideas what I'm doing wrong here?

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• Remove from a std::set<shared_ptr<T>> by T*

  - by Autopulated

  I have a set of shared pointers: std::set<boost::shared_ptr<T>> set; And a pointer: T* p; I would like to efficiently remove the element of set equal to p, but I can't do this with any of the members of set, or any of the standard algorithms, since T* is a completely different type to boost::shared_ptr<T>. A few approaches I can think of are: somehow constructing a new shared_ptr from the pointer that won't take ownership of the pointed to memory (ideal solution, but I can't see how to do this) wrapping / re-implementing shared_ptr so that I can do the above just doing my own binary search over the set Help!

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• how to make a program like fraps.

  - by blood

  i want to make a program that will capture video. what if the best way to captrue the video, i know c++ and im learning assembly and i found in my assembly book i can get data from the video card i think? would that be the best way? i know fraps hooks into programs but i want my program to take the full screen? so i want something fast low memory useage if i can and something i can use on other computers with them having the same hardware.

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• [Ruby] How can I randomly iterate through a large Range?

  - by void

  I would like to randomly iterate through a range. Each value will be visited only once and all values will eventually be visited. For example: (0..9).sort_by{rand}.map{|x| f(x)} where f(x) is some function that operates on each value. A Fisher-Yates shuffle could be used to increase efficiency, but this code is sufficient for many purposes. My problem is that sort_by will transform the range into an array, which is not cool because I am working with astronomically large numbers. Ruby will quickly consume a large amount of RAM trying to create a monstrous array. This is also why the following code will not work: tried = {} # store previous attempts bigint = 99**99 bigint.times { x = rand(bigint) redo if tried[x] tried[x] = true f(x) # some function } This code is very naive and quickly runs out of memory as tried obtains more entries. What sort of algorithm can accomplish what I am trying to do?

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• Howto check if a object is connected to another in hibernate

  - by codevourer

  Imagine two domain object classes, A and B. A has a bidirectional one-to-many relationship to B. A is related to thousands of B. The relations must be unique, it's not possible to have a duplicate. To check if an instance of B is already connected to a given instance of A, we could perform an easy INNER JOIN but this will only ensure the already persisted relations. What about the current transient relations? class A { @OneToMany private List<B> listOfB; } If we access the listOfB and perform a check of contains() this will fetch all the connected instances of B lazy from the datasource. I only want to validate them by their primary-key. Is there an easy solution where I can do things like "Does this instance of A is connected with this instance of B?" Without loading all these data into memory and perform a based on collections?

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• Inheriting database connection in PHP OOP

  - by vrode

  My abstract class Database is made for database interaction and any child of this class (UserDatabase, ActionDatabase, EventDatabase) inherits its database connection which is defined as static. `abstract class Database { static $connection = mysql_connect( ); } class UserDatabase extends Database { ... public function __construct( ) { $connection ? "connected" : "not connected"; $this-table = "users"; mysql_query( "FROM " . $this-table . " SELECT *" ); } } ` Does that mean, that my database connection is only set up and stored in memory once and passed on to subclasses as reference without being replicated for each instance? Is this how you would implement you OOP-correct database interface?

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• Forcing a templated object to construct from a pointer

  - by SalamiArmi

  I have a fictional class: template<typename T> class demonstration { public: demonstration(){} ... T *m_data; } At some point in the program's execution, I want to set m_data to a big block of allocated memory and construct an object T there. At the moment, I've been using this code: void construct() { *m_data = T(); } Which I've now realised is probably not the best idea... wont work under certain cirumstances, if T has a private assignment operator for example. Is there a normal/better way to do what I'm attempting here?

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• Freeing JavaScript object

  - by pion

  I am looking at the example from http://www.javascriptkit.com/javatutors/oopjs.shtml var person = new Object() person.name = "Tim Scarfe" person.height = "6Ft" But there is no mention how to "free" it in order to avoid memory leak. Will the following code free it? person = null; How do you free a JavaScript Object using "new Object()? How do you free a JavaScript Array allocated using "new Array(10)"? How do you free a JavaScript JSON allocated using "var json = {"width": 480, "height": 640}"? Thanks in advance for your help.

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• Double indirection and structures passed into a function

  - by ZPS

  I am curious why this code works: typedef struct test_struct { int id; } test_struct; void test_func(test_struct ** my_struct) { test_struct my_test_struct; my_test_struct.id=267; *my_struct = &my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); } This works, but pointing to the memory address of a functions local variable is a big no-no, right? But if i used a structure pointer and malloc, that would be the correct way, right? void test_func(test_struct ** my_struct) { test_struct *my_test_struct; my_test_struct = malloc(sizeof(test_struct)); my_test_struct->id=267; *my_struct = my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); }

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• how to read httpWebRequest's request stream in c#, i got error" the stream is not readable" ?

  - by sam

  hi i want to read request stream from a custom httpWebRequest class that inherits from httpWebRequest and i have tried to read the request stream in different stages but sitll not sure how to archieve that in the class,thanks very much for any help. This custom httpWebRequest is used to serilize soap message and i want to know what request has been sent in string format. I also implemented custom HttpRequestCreator,HttpWebResponse but till cant find a place/stage i can read the request stream. If i output everything in a memory stream then copy the content to request stream, anyone knows which stage i can do it in the constructor, BeginGetRequestStream,EndGetRequestStream or GetRequestStream?

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• How do I choose a database?

  - by liamzebedee

  I need a comparison table of some sort for database varieties (MySQL, SQLite etc.). I can't find one. My use case is, I am implementing storage of objects in a distributed hash table. I need a database solution that is: Fast for sorting Simplistic (no users, preferably no additional structures like multiple tables etc.) Concurrent (if possible) Multi-platform File based (not stored in memory primarily) Centralized I will be programming in Go. As I understand, I believe I need what is called a Document Orientated Database, because I am storing objects, identified by keys. EDIT: While I am implementing a DHT, I will also be storing metadata about the objects, such as access counts etc. It would also be preferable to have TLL (time to live)

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• How do I write raw binary data in Python?

  - by Chris B.

  I've got a Python program that stores and writes data to a file. The data is raw binary data, stored internally as str. I'm writing it out through a utf-8 codec. However, I get UnicodeDecodeError: 'charmap' codec can't decode byte 0x8d in position 25: character maps to <undefined> in the cp1252.py file. This looks to me like Python is trying to interpret the data using the default code page. But it doesn't have a default code page. That's why I'm using str, not unicode. I guess my questions are: How do I represent raw binary data in memory, in Python? When I'm writing raw binary data out through a codec, how do I encode/unencode it?

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• Implications of Fulltext Search over many columns

  - by Alex

  Hello, I have a really wide table which includes separate columns for billing address, shipping address, primary address, names, aliases etc. (I can't normalize this table further, and that's not the question here anyways). I'm implementing SQL Server fulltext search, and I'm wondering whether I should limit the search ability to just the primary fields (primary address and names for example), or if I can extend the search ability across all columns without occurring too much of a performance or memory penalty. I've done some basic testing with 10,000 sample rows and it's quite fast but I don't have much experience with fulltext indexing, especially its dictionary internals, so I don't know if the index is going to grow over time, or if there is anything else to consider. Thoughts?

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• Retrieving data from an encrypted text file?

  - by user

  Let's say I have a text file contains my data. data : ab bc de - encrypted data on text file : ba cb ed I want to find bc from text file, so I have to decrypt the text file with this code : SL:=TStringList.create; SL.LoadFromFile(textfile) SLtemp:=TStringList.create; for I := 0 to SL.Count - 1 do SLtemp.Add(ReverseString(SL[i])); //decrypt SL.Free; for I := 0 to SLtemp.Count - 1 do if SLtemp[i] = 'bc' then begin showmessage('found'); break; end; SLtemp.Free; I think my way is wasting resources. I have to load whole file to memory and decrypt them. I need some suggestions here to find quickly a specific line from an encrypted text. Thanks.

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• How are a session identifiers generated?

  - by Asaf R

  Most web applications depend on some kind of session with the user (for instance, to retain login status). The session id is kept as a cookie in the user's browser and sent with every request. To make it hard to guess the next user's session these session-ids need to be sparse and somewhat random. The also have to be unique. The question is - how to efficiently generate session ids that are sparse and unique? This question has a good answer for unique random numbers, but it seems not scalable for a large range of numbers, simply because the array will end up taking a lot of memory.

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• Detect movie being played (Windows)

  - by modosansreves

  Watching a movie is quite a different user activity. User doesn't touch neither mouse nor keyboard. Yet he 'actively' uses the computer. Thus, screensaver shouldn't run, indexing should be performed with care etc. On the other side, playing video requires either using direct write to video memory, or DirectShow, or some other API. This may be the key to the answer. What is the Dead Simple Way to determine that a video is being played?

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• In C, as free() knows an array size, why isn't there a function that gets the array size? [closed]

  - by user354959

  Possible Duplicate: If free() knows the length of my array, why can’t I ask for it in my own code? Searching around (including here at stackoverflow), I got that malloc() allocates an array and also creates a header to control the array info. In this header, there's also the array size. free() use such information to know how to deallocate that array. So, if the array size info is "there" (somewhere in the memory), why there isn't a function that returns an array size, looking for this at the array header? Or am I missing something?

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• Is it possible to give a python dict an initial capacity (and is it usefull)

  - by Peter Smit

  I am filling a python dict with around 10,000,000 items. My understanding of dict (or hashtables) is that when too much elements get in them, the need to resize, an operation that cost quite some time. Is there a way to say to a python dict that you will be storing at least n items in it, so that it can allocate memory from the start? Or will this optimization not do any good to my running speed? (And no, I have not checked that the slowness of my small script is because of this, I actually wouldn't now how to do that. This is however something I would do in Java, set the initial capacity of the HashSet right)

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• What segments does C compiled program use?

  - by b-gen-jack-o-neill

  Hi, I read on OSDev wiki, that protected mode of x86 architecture allow you to create separate segments for code and data, while you cannot write into code section. That Windows (yes, this is the platform) loads new code into code segment, and data are created on data segment. But, if this is the case, how does program know it must switch segments to the data segment? Becouse if I understand it right, all adress instructions point to the segment you run the code from, unless you switch the descriptor. But I also read, that so colled flat memory model allows you to run code and data within one segment. But I read this only in connection to assembler. So, please, what is the case with C compiled code on Windows? Thanks.

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• Is there any significant benefit to reading string directly from control instead of moving it into a

  - by Kevin

  sqlInsertFrame.Parameters.AddWithValue("@UserName", txtUserName.txt); Given the code above...if I don't have any need to move the textbox data into a string variable, is it best to read the data directly from the control? In terms of performance, it would seem smartest to not create any unnecessary variables which use up memory if its not needed. Or is this a situation where its technically true but doesn't yield any real world results due to the size of the data in question. Forgive me, I know this is a very basic question.

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• Easiest way to combine a dataset and other data in a single file?

  - by Tim Gradwell

  I have a dataset in C# which I can serialise using dataset.WriteXml(filename); but I want the file to contain other data as well (essentially some meta data about the dataset). I could add another table to the dataset which contained the metadata, but I'd prefer to keep it separate, if at all possible. Essentially I think I want to create a 'combination of files' file, that looks something like this: size_of_file1 file1 size_of_file2 file2 ... etc Then, I'd like to load the file into memory, and split the file into separate streams, so that I can feed the dataset into dataset.ReadXml(stream); and the metadata into something else. Sound possible? Can anyone tell me how I can do it? Thanks Tim

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• storing an integer constant other than zero in a pointer variable

  - by benjamin button

  int main() { int *d=0; printf("%d\n",*d); return 0; } this works fine. >cc legal.c > ./a.out 0 if i change the statement int *d=0; to int *d=1; i see the error. cc: "legal.c", line 6: error 1522: Cannot initialize a pointer with an integer constant other than zero. so its obvious that it will allow only zero.i want to know what happens inside the memory when we do this int *d=0 which is making it valid syntax. I am just asking this out of curiosity!

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• how can i set mTextView to show on button click

  - by Ajay Pandey

  i have a UITextView object which i have created in interface builder with it's hidden property unmarked.Now i want this textView to be invisible when my application launches and first view appears.Further i want it to be displayed when a particular method is called.Now this is what i have written in view did load [mTextView setHidden:YES]; self.mTextView=[[UITextView alloc] init]; it hides the textView ats the first view appears but when my desired method is called and i write [mTextView setHidden:NO]; it does not show it again.. Is it like we cant change the appearance of a textView once it is assigned because after assigning memory as self.mTextView=[[UITextView alloc] init]; and then writing [mTextView setHidden:YES]; it does not hide textView in viwDidLoad either.....

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• Is it faster to use a complicated boolean to limit a ResultSet at the MySQL end or at the Java end?

  - by javanix

  Lets say I have a really big table filled with lots of data (say, enough not to fit comfortably in memory), and I want to analyze a subset of the rows. Is it generally faster to do: SELECT (column1, column2, ... , columnN) FROM table WHERE (some complicated boolean clause); and then use the ResultSet, or is it faster to do: SELECT (column1, column2, ... , columnN) FROM table; and then iterate over the ResultSet, accepting different rows based on a java version of your boolean condition? I think it comes down to whether the Java iterator/boolean evaluator is faster than the MySQL boolean evaluator.

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