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• Preparing for the next C++ standard

  - by Neil Butterworth

  The spate of questions regarding BOOST_FOREACH prompts me to ask users of the Boost library what (if anything) they are doing to prepare their code for portability to the proposed new C++ standard (aka C++0x). For example, do you write code like this if you use shared_ptr: #ifdef CPPOX #include <memory> #else #include "boost/shared_ptr.hpp" #endif There is also the namespace issue - in the future, shared_ptr will be part of the std, namespace - how do you deal with that? I'm interested in these questions because I've decided to bite the bullet and start learning boost seriously, and I'd like to use best practices in my code. Not exactly a flood of answers - does this mean it's a non-issue? Anyway, thanks to those that replied; I'm accepting jalfs answer because I like being advised to do nothing!

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• Released object crashes app

  - by John Smith

  I am using objective-C++ (+Boost) for iPhone development. I am in a rather tight loop and need to allocate and release a certain object. The code is something like this. for (int i=0;i<100;i++) { opt = [[FObj alloc] init]; //do stuff with opt [opt release]; } The FObj object is something like @interface FObj MyCPPObj * cppobj; @end In the implementation of FObj there is a dealloc method: -(void) dealloc { delete cppobj; //previously allocated with 'new' [super dealloc]; } I am afraid that if i don't release then the 'MyCPPObj's will just pile up. But releasing makes the app crash after the first loop. What am I doing wrong? Or perhaps should I make cppobj and boost::shared_ptr? (do boost shared pointers automatically release their objects when an objective-C++ object is deleted?)

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• AJAX Autocomplete appears at a random vertical position, not touching the textbox

  - by Tim

  Hi, I am using the AJAX Autocomplete extender for ASP.NET 2. Everything works fine...I am calling a webservice which gets me the values to fill the drop down with after 3 letters are typed into certain es. I have set the maxheight attribute and am using a scrollbar in case there are more entries than would fit that height. However, I notice that in some cases, the drop down appears at a random position on the screen, i.e. rather than connected to the relevant textbox, sometimes it appears with its entries above the textbox, not touching it at all. Sometimes it would have just one entry and it would appear in the middle of the screen vertically above the textbox it is associated to. Is there a reason why this is happening?

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• Random Record from Recordset

  - by Tony Hanks

  I have the fillowing Query: SELECT a.*, ps4_media.filename, ps4_galleries.name as galleryname, ps4_media_iptc.description, ps4_media_iptc.title, ps4_media_iptc.headline, ps4_media.date_added, ps4_galleries.created, ps4_folders.name as foldername, ps4_galleries.gallery_count FROM ps4_media_galleries a INNER JOIN (SELECT ps4_media_galleries.gallery_id, min(ps4_media_galleries.gmedia_id) AS minID FROM ps4_media_galleries GROUP BY ps4_media_galleries.gallery_id) b ON a.gallery_id = b.gallery_id AND a.gmedia_id = b.minID INNER JOIN ps4_media ON ps4_media.media_id = a.gmedia_id INNER JOIN ps4_folders ON ps4_folders.folder_id = ps4_media.folder_id INNER JOIN ps4_galleries ON ps4_galleries.gallery_id = a.gallery_id INNER JOIN ps4_media_iptc ON ps4_media_iptc.media_id = a.gmedia_id ORDER BY ps4_galleries.created DESC How do I get ps4_media.filename to be random, everything else is fine just want the thumbnail which ps4_media.filename is to be and of the records in the found set.

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• PHP - displaying 1 random record for each week

  - by mike

  I want to display 1 random record from a database based on the week. I need to determine if it's a new, and if it is a new week, then select the record and display the new record. I'm thinking I can just use a single day of the week to generate the new record, either way will work. I'm really having a hard time conceptualizing how I'll store the record id and not select a new one when someone visits again the same day or refreshes the page. Any ideas? Let me know if I wasn't clear enough.

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• Random password variable disappears

  - by snaken

  Hi, I'm using the following to generate a random password in a shell script: DBPASS=</dev/urandom tr -dc A-Za-z0-9| (head -c $1 > /dev/null 2>&1 || head -c 8) When i run this in a file on its own like this: #!/bin/sh DBPASS=</dev/urandom tr -dc A-Za-z0-9| (head -c $1 > /dev/null 2>&1 || head -c 8) echo $DBPASS A password is echoed. When i incorporate it into a larger script though the variable never seems to get created for some reason, so for example this doesn't work: DBPASS=</dev/urandom tr -dc A-Za-z0-9| (head -c $1 > /dev/null 2>&1 || head -c 8) sed -i s/oldpass/$DBPASS/ mysql_connect.php If i manually set the variable though everything is fine.. can anyone see why?

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• Get result type of function

  - by Robert

  I want to specialize a template function declared as: template<typename Type> Type read(std::istream& is); I then have a lot of static implementations static int read_integer(std::istream& is); a.s.o. Now I'd like to do a macro so that specialization of read is as simple as: SPECIALIZE_READ(read_integer) So I figured I'd go the boost::function_traits way and declare SPECIALIZE_READ as: #define SPECIALIZE_READ(read_function) \ template<> boost::function_traits<read_function>::result_type read(std::istream& is) { \ return read_function(is); \ } but VC++ (2008) compiler complains with: 'boost::function_traits' : 'read_integer' is not a valid template type argument for parameter 'Function' Ideas ?

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• Is generating real random numbers this easy in C#?

  - by JL

  I found this code using Google. private int RandomNumber(int min, int max) { Random random = new Random(); return random.Next(min, max); } Is this really all there is to generating REAL random numbers in C#? I intend to generate on a small scale between values 1-10. Thanks

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• Order by Rand - How can I do in CouchDB?

  - by Lucas Renan

  I need a random query, but I don't know what's the best way to do this in the view.

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• Generating unique N-valued key

  - by Bar

  Hi, StackOverflow! I want to generate unique random, N-valued key. This key can contain numbers and latin characters, i.e. A-Za-z0-9. The only solution I am thinking about is something like this (pseudocode): key = ""; smb = "ABC…abc…0123456789"; // allowed symbols for (i = 0; i < N; i++) { key += smb[rnd(0, smb.length() - 1)]; // select symbol at random position } Is there any better solution? What can you suggest? TIA, Michael.

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• Order By Rand by Time (HQL)

  - by Felipe

  Hi all, I'm developing a web application using asp.net Mvc 2 and NHibernate, and I'm paging data (products in a category) in my page, but this data are random, so, I'm using a HQL statement link this: string hql = "from Product p where p.Category.Id=:IdCategory order by rand()"; It's working fine, but when I page, sometimes the same product appears in the first, second, etc... pages because it's order by rand(). Is there any way to make a random order by fixed by period (time internal) ? Or any solution ? thanks Cheers

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• C# how to quickly create dummy image directly in code

  - by PaN1C_Showt1Me

  How to quickly create some random image with the icon size? I don't want to use neither Image.FromFile, nor Image.FromStream

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• Linq to NHibernate, Order by Rand() ?

  - by Felipe

  Hi everybody, I'm using Linq To Nhibernate, and with a HQL statement I can do something like this: string hql = "from Entity e order by rand()"; Andi t will be ordered so random, and I'd link to know How can I do the same statement with Linq to Nhibernate ? I try this: var result = from e in Session.Linq<Entity> orderby new Random().Next(0,100) select e; but it throws a exception and doesn't work... is there any other way or solution? Thanks Cheers

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• How to increment counters based on a printed array

  - by Sam Liew

  I managed to developed a simple board of 5x5 using random numbers and array. Big achievement for someone like me! :) Now I have to increment the counters depending on the frequency of the numbers. If the value within 0-49 is printed..then nCounter++ If the value within 50-75 is printed..then pCounter++ something like that. The problem is that I don't know how to increase the counters based on the printed board. Here is the code: #include <stdio.h> #include <stdlib.h> #include <time.h> int main() { //Initialize Variables int randomNumber; int rows; int columns; int hdCounter =0; int hCounter = 0; int cCounter = 0; int pCounter = 0; int nCounter = 0; //Declare board size int board[5][5]; //size of board is 5 x 5 //Create the random number generator seed srand(time(NULL)); //Assign the random numbers from 1 - 25 into variable randomNumber //Create the rows for the board for ( rows = 1; rows <= 5 ; rows++ ) { //Create the colimns for the board for ( columns = 1; columns <= 5 ; columns++ ) { //Assign variable randomNumber into variable board randomNumber = rand() %100 + 1; board[rows][columns] = randomNumber; //print the board printf("%d\t", board[rows][columns]); //calculate the frequency of numbers on the printed board if (randomNumber >= 85 && randomNumber <= 100 ) hdCounter++; else if ( randomNumber >= 75 ) hCounter++; else if ( randomNumber >= 65 ) cCounter++; else if ( randomNumber >= 50 ) pCounter++; else if ( randomNumber >= 1 ) nCounter++; else continue; } //Newline after the end of 5th column. printf("\n\n"); } printf( "N \t P \t C \t H \t HD\n\n" ); printf("%d \t %d \t %d \t %d \t %d \t", nCounter, pCounter, cCounter, hCounter, hdCounter); }//end main I tried replacing randomNumber in the if-statement with board[rows][columns] but I seem to get the same undesired results.

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• how to quickly create dummy image directly in .NET code

  - by PaN1C_Showt1Me

  How to quickly create some random image with the icon size? I don't want to use neither Image.FromFile, nor Image.FromStream

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• How to get unique numbers using randomint python?

  - by user2519572

  I am creating a 'Euromillions Lottery generator' just for fun and I keep getting the same numbers printing out. How can I make it so that I get random numbers and never get the same number popping up: from random import randint numbers = randint(1,50) stars = randint(1,11) print "Your lucky numbers are: ", numbers, numbers, numbers, numbers, numbers print "Your lucky stars are: " , stars, stars The output is just: >>> Your lucky numbers are: 41 41 41 41 41 >>> Your lucky stars are: 8 8 >>> Good bye! How can I fix this? Regards

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• Characteristics of an Initialization Vector

  - by Jamie Chapman

  I'm by no means a cryptography expert, I have been reading a few questions around Stack Overflow and on Wikipedia but nothing is really 'clear cut' in terms of defining an IV and it's usage. Points I have discovered: An IV is pre-pended to a plaintext message in order to strengthen the encryption The IV is truely random Each message has it's own unique IV Timestamps and cryptographic hashes are sometimes used instead of random values, but these are considered to be insecure as timestamps can be predicted One of the weaknesses of WEP (in 802.11) is the fact that the IV will reset after a specific amount of encryptions, thus repeating the IV I'm sure there are many other points to be made, what have I missed? (or misread!)

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• Choose item from a list with bias?

  - by ooboo

  Given a list of items x1 ... xn and associated probabilties p1 ... pn that sum up to 1 there's a well known procedure to select a random item with its associated proabability by sorting the list according to weight, choosing a random value between 1 and 0, and adding up to a culmination sum until it exceeds the value selected and return the item at this point. So if we have x1 - 0.5, x2 - 0.3, x3 - 0.2, if the randomly chosen value is less than 0.5 x1 will be chosen, if between 0.5 and 0.8, x2, and else x3. This requires sorting so it needs O(nlogn) time. Is there anything more efficient than that?

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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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• Mean of Sampleset and powered Sampleset

  - by Milla Well

  I am working on an ICA implementation wich is based on the assumption, that all source signals are independent. So I checked on the basic concepts of Dependence vs. Correlation and tried to show this example on sample data from numpy import * from numpy.random import * k = 1000 s = 10000 mn = 0 mnPow = 0 for i in arange(1,k): a = randn(s) a = a-mean(a) mn = mn + mean(a) mnPow = mnPow + mean(a**3) print "Mean X: ", mn/k print "Mean X^3: ", mnPow/k But I couldn't produce the last step of this example E(X^3) = 0: >> Mean X: -1.11174580826e-18 >> Mean X^3: -0.00125229267144 First value I would consider to be zero, but second value is too large, isn't it? Since I subtract the mean of a, I expected the mean of a^3 to be zero as well. Does the problem lie in the random number generator, the precision of the numerical values in my misunderstanding of the concepts of mean and expected value?

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• How to get some randomized concats based on 2 columns from 1 table?

  - by Nils Riedemann

  Hey folks, i have a large user Database (13k+), and for some reason i need to create random names. The users table has "first_name" and "last_name". Now i want to have 10 concats of full_name and last_name of two completely random rows. Is that even possible with SQL? My other idea was just to create a full_names and last_names table … but that would'nt be as much challenging. Oh, and it should not take up too much performance :) (so order by rand() is not an option ;))

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• How many double numbers are there between 0.0 and 1.0?

  - by polygenelubricants

  This is something that's been on my mind for years, but I never took the time to ask before. Many (pseudo) random number generators generate a random number between 0.0 and 1.0. Mathematically there are infinite numbers in this range, but double is a floating point number, and therefore has a finite precision. So the questions are: Just how many double numbers are there between 0.0 and 1.0? Are there just as many numbers between 1 and 2? Between 100 and 101? Between 10^100 and 10^100+1? Note: if it makes a difference, I'm interested in Java's definition of double in particular.

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• C++ function for picking from a list where each element has a distinct probability

  - by Stuart

  I have an array of structs and one of the fields in the struct is a float. I want to pick one of the structs where the probability of picking it is relative to the value of the float. ie struct s{ float probability; ... } sArray s[50]; What is the fastest way to decide which s to pick? Is there a function for this? If I knew the sum of all the probability fields (Note it will not be 1), then could I iterate through each s and compare probability/total_probability with a random number, changing the random number for each s? ie if( (float) (rand() / RAND_MAX) < probability)...

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• python -> combinations of numbers and letters

  - by tekknolagi

  #!/usr/bin/python import random lower_a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] upper_a = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'] num = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'] all = [] all = " ".join("".join(lower_a) + "".join(upper_a) + "".join(num)) all = all.split() x = 1 c = 1 while x < 10: y = [] for i in range(c): a = random.choice(all) y.append(a) print "".join(y) x += 1 c += 1 what i have now outputs something like the following: 5 hE HAy 1kgy Pt6JM 2pFuCb Jv5osaX 5q8PwWAO SvHWRKfI5 how can i make it systematically go through every combination of letters (upper and lowercase) for a given length, then add 1 to that length and repeat the process?

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• remove the spaces...

  - by tekknolagi

  !/usr/bin/python import random lower_a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] upper_a = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'] num = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9'] all = [] all = " ".join("".join(lower_a) + "".join(upper_a) + "".join(num)) all = all.split() x = 0 while x < 10: for i in range(7): a = random.choice(all) print a, print x += 1 what i want to do is remove the spaces from the output what it gives now is Z 3 a A I K R G B i N 9 c E v g E r A N 8 e B 6 d v H O c a V 8 c x y b g 2 W a T T f 8 H T r 6 E p D K l 5 p u x q 8 P Z 9 T n I W X n B Q

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