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  • Simple java syncrhonization question

    - by Misha Koshelev
    Dear All: Was wondering, which is correct: Option One class A { public void methodOne() { synchronized(this) { modifyvalue notifyAll() } } public void methodTwo() { while (valuenotmodified) { synchronized(this) { wait() } } } Option Two class A { public void methodOne() { modifyvalue synchronized(this) { notifyAll() } } public void methodTwo() { while (valuenotmodified) { synchronized(this) { wait() } } } and why? Thank you Misha

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  • Simple dynamic memory allocation bug.

    - by M4design
    I'm sure you (pros) can identify the bug's' in my code, I also would appreciate any other comments on my code. BTW, the code crashes after I run it. #include <stdlib.h> #include <stdio.h> #include <stdbool.h> typedef struct { int x; int y; } Location; typedef struct { bool walkable; unsigned char walked; // number of times walked upon } Cell; typedef struct { char name[40]; // Name of maze Cell **grid; // 2D array of cells int rows; // Number of rows int cols; // Number of columns Location entrance; } Maze; Maze *maz_new() { int i = 0; Maze *mazPtr = (Maze *)malloc(sizeof (Maze)); if(!mazPtr) { puts("The memory couldn't be initilised, Press ENTER to exit"); getchar(); exit(-1); } else { // allocating memory for the grid mazPtr->grid = (Cell **) malloc((sizeof (Cell)) * (mazPtr->rows)); for(i = 0; i < mazPtr->rows; i++) mazPtr->grid[i] = (Cell *) malloc((sizeof (Cell)) * (mazPtr->cols)); } return mazPtr; } void maz_delete(Maze *maz) { int i = 0; if (maz != NULL) { for(i = 0; i < maz->rows; i++) free(maz->grid[i]); free(maz->grid); } } int main() { Maze *ptr = maz_new(); maz_delete(ptr); getchar(); return 0; } Thanks in advance.

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  • Need simple advice for graph solving problem

    - by sap
    Hi there, a collegue of mine proposed to me an exercise from an online judge website, which is basically a graph solving problem of an evacuation plan on a small town. i dont need the answer (nor do i want it) i just need an advice on which is the best approach to solving it since im kinda new to these kind of problems. the problem consists of town buildings with workers and fallout shelters in case of a nuclear attack. i have to build an algorithm that will assign the workers of each building to one or more fallout shelters but in a way that some shelters wont became too overcrowded while others remain almost empty (else i would just make the workers go to the nearest one). the problem is this: http://acm.timus.ru/problem.aspx?space=1&num=1237 in case its offline heres the google cached version of it: http://webcache.googleusercontent.com/search?q=cache:t2EPCzezs7AJ:acm.timus.ru/problem.aspx%3Fspace%3D1%26num%3D1237+vladimir+kotov+evacuation+problem&cd=1&hl=pt-PT&ct=clnk&gl=pt what i've done so far is for each building get the nearest shelter and move the number of workers from that build equal to the shelter capacity. then move to the next building. but sometimes the number of workers is greater than the shelter capacity, in that case after i iterate through every building, ill just iterate then again apllying the same algorithm until every building has 0 workers in it, problem is this is hardly the best way to solve it. any tip is welcome, please dont feel like im asking for the answer, i just want an advice in the right direction of solving it. thanks in advance.

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  • GORM column names for simple one to many mapping

    - by Toby Hobson
    I have this setup class User { Date lastLogin // logins is a history of logins static hasMany = [logins : Date] def setLastLogin(Date date) { if (date) { lastLogin = date addToLogins(date) } } } GORM is generating a table MEMBER_LOGINS which currently looks like this: USER_ID, LOGINS Instead I would like USER_ID, DATE I tried adding a mapping in User static mapping = { logins column: 'date'; } But that just changed the foreign key so i now have DATE, LOGINS How can I change the LOGINS column? Thanks!

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  • Simple vector program error

    - by Codeguru
    Hi iam new to c++ and iam trying out this vector program and i am getting the following error: error: conversion from test*' to non-scalar typetest' requested| Here is the code include include include include using namespace std; class test{ string s; vector <string> v; public: void read(){ ifstream in ("c://test.txt"); while(getline(in,s)) { v.push_back(s); } for(int i=0;i<v.size();i++) { cout<<v[i]<<"\n"; } } }; int main() { cout<<"Opening the file to read and displaying on the screen"< }

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  • how do simple SQLAlchemy relationships work?

    - by Carson Myers
    I'm no database expert -- I just know the basics, really. I've picked up SQLAlchemy for a small project, and I'm using the declarative base configuration rather than the "normal" way. This way seems a lot simpler. However, while setting up my database schema, I realized I don't understand some database relationship concepts. If I had a many-to-one relationship before, for example, articles by authors (where each article could be written by only a single author), I would put an author_id field in my articles column. But SQLAlchemy has this ForeignKey object, and a relationship function with a backref kwarg, and I have no idea what any of it MEANS. I'm scared to find out what a many-to-many relationship with an intermediate table looks like (when I need additional data about each relationship). Can someone demystify this for me? Right now I'm setting up to allow openID auth for my application. So I've got this: from __init__ import Base from sqlalchemy.schema import Column from sqlalchemy.types import Integer, String class Users(Base): __tablename__ = 'users' id = Column(Integer, primary_key=True) username = Column(String, unique=True) email = Column(String) password = Column(String) salt = Column(String) class OpenID(Base): __tablename__ = 'openid' url = Column(String, primary_key=True) user_id = #? I think the ? should be replaced by Column(Integer, ForeignKey('users.id')), but I'm not sure -- and do I need to put openids = relationship("OpenID", backref="users") in the Users class? Why? What does it do? What is a backref?

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  • Problem accessing variable in a nested form partial

    - by brad
    I have a nested form in a rails view that is called like this <% f.fields_for :invoice_item_numbers do |item_no_form| %> <%= render 'invoice_item_number', :f => item_no_form %> <% end %> and the partial (_invoice_item_number.html.erb) looks like this <div class='invoice_item_numbers'> <% if f.object.new_record? %> <li><%= f.label :item_number %><%= f.text_field :item_number %> <%= link_to_function "remove", "$(this).parent().remove()", :class => 'remove_link' %></li> <% else %> <li class="inline"><%= f.label :item_number %><%= f.text_field :item_number %> </li><li class="inline"><%= f.label :description %><%= invoice_item_number.description %></li><li><%= f.label :amount %><%= f.text_field :amount %> <%= f.check_box '_destroy', :class => 'remove_checkbox' %> <%= f.label '_destroy', 'remove', :class => 'remove_label' %></li> <% end %> </div> This fails with the error message undefined method `description' for nil:NilClass Why does invoice_item_number return a nil object in this partial? It is obviously being defined somehow because if I change it to something else (e.g. item_number.description then the error message becomes undefined local variable or methoditem_number' for #instead. The invoice_item_number object that is being displayed by this partial is being used perfectly well by the form helpers as<%= f.text_field :item_number %and<% f.text_field :amount %both work perfectly well. I have tried a number of solutions such as using@invoice_item_number` and explicitly defining an object in the render method but these have not worked. Presumably there is a very simple answer to this.

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  • I need a simple command line program to transform XML using XSLT

    - by fuzzy lollipop
    I am on OSX Snow Leopard (10.6.2) I can install anything I need to. I would preferably like a Python or Java solution. I have searched on Google and found lots of information on writing my own program to do this, but this is a just a quick and dirty experiment so I don't want to invest a lot of time on writing a bunch of code to do this, I am sure someone else has done this already.

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  • Passing variables from a thread to another form using C#

    - by kirstom14
    Hi, I am trying to pass 2 variables from a thread, in the MainForm, to another form, but when doing so an error occurs. private void TrackingThread( ) { float targetX = 0; float targetY = 0; while ( true ) { camera1Acquired.WaitOne( ); camera2Acquired.WaitOne( ); lock ( this ) { // stop the thread if it was signaled if ( ( x1 == -1 ) && ( y1 == -1 ) && ( x2 == -1 ) && ( y2 == -1 ) ) { break; } // get middle point targetX = ( x1 + x2 ) / 2; targetY = ( y1 + y2 ) / 2; } if (directionForm != null) { directionForm.RunMotors(targetX, targetY); } } } In the form, directionForm, I am simply displaying the variables targetX and targetY. The code for the directionForm.RunMotors() is the following: public void RunMotors(float x, float y) { label1.Text = "X-ordinate " + x.ToString(); label2.Text = "Y-ordinate " + y.ToString(); } The error happen when I am trying to display the two variables: "InvalidOperationException was unhandled Cross-threading operation not valid: Control label1 accessed from a thread other than . the thread it was created on" What shall I do??? Thanks in advance

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  • CarrierWave and nested forms saving empty image object if photo :title is included in form

    - by Wasabi Developer
    I'm after some advice in regards to handling nested form data and I would be ever so grateful for any insights. The trouble is I'm not 100% sure why I require the following code in my model accepts_nested_attributes_for :holiday_image, allow_destroy: true, :reject_if => lambda { |a| a[:title].blank? } If I don't understand why I require to tact on on my accepts_nested_attributes_for association: :reject_if => lambda { |a| a[:title].blank? } If I remove this :reject_if lambda, it will save a blank holiday photo object in the database. I presume because it takes the :title field from the form as an empty string? I guess my question is, am I doing this right or is there a better way of this this within nested forms if I want to extend my HolidayImage model to include more strings like description, notes? Sorry If I can't be more succinct. My simple holiday app. # holiday.rb class Holiday < ActiveRecord::Base has_many :holiday_image accepts_nested_attributes_for :holiday_image, allow_destroy: true, :reject_if => lambda { |a| a[:title].blank? } attr_accessible :name, :content, :holiday_image_attributes end I'm using CarrierWave for image uploads. # holiday_image.rb class HolidayImage < ActiveRecord::Base belongs_to :holiday attr_accessible :holiday_id, :image, :title mount_uploader :image, ImageUploader end Inside my _form partial there is a field_for block <h3>Photo gallery</h3> <%= f.fields_for :holiday_image do |holiday_image| %> <% if holiday_image.object.new_record? %> <%= holiday_image.label :title, "Image Title" %> <%= holiday_image.text_field :title %> <%= holiday_image.file_field :image %> <% else %> Title: <%= holiday_image.object.title %> <%= image_tag(holiday_image.object.image.url(:thumb)) %> Tick to delete: <%= holiday_image.check_box :_destroy %> <% end %> Thanks again for your patience.

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  • PHP: Simple, Validate if string is hex?

    - by oni-kun
    I have no clue how to validate this string. I am simply supplying an IV for an encryption, but can find no "is_hex()" or similar function, I can't wrap my head around it! I read on a comment in the php documentation (user contrib. notes) this: if($iv == dechex(hexdec($iv))) { //True } else { //False } But that doesn't seem to work at all.. It only says false. If it helps my input of my IV would be this: 92bff433cc639a6d

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  • Running a simple VBA script to test a connection

    - by brohjoe
    I'm trying to test the connection of a GoDaddy SQL Server database. I'm getting an 'invalid connection string attribute.' What's wrong with this script? Dim cnn As ADODB.Connection Dim canConnect As Boolean Public Sub TestConnection() Set cnn = New ADODB.Connection cnn.Open "Provider=sqloledb;Data Source=GoDaddyServer.com;Initial Catalog=dBase1;UserID=userID; Password='password';" If cnn.State = adStateOpen Then canConnect = True cnn.Close End If MsgBox canConnect End Sub

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  • simple python file writing question

    - by aharon
    I'm learning Python, and have run into a bit of a problem. On my OSX install of Python 3.1, this happens in the console: >>> filename = "test" >>> reader = open(filename, 'r') >>> writer = open(filename, 'w') >>> reader.read() '' >>> writer.write("hello world\n") 12 >>> reader.read() '' And calling more test in BASH confirms that there is nothing in test. What's going on? Thanks.

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  • Simple Tableless Positioning issue: Trying to float Div right on same line

    - by MrEnder
    Ok I just started a template for a website http://clickforclicks.com/design1/ I'm trying to make it tableless. Notice I have a red div along the side. I tried to get one on the otherside aswell that looked the same. But when I do it. It goes to a new line =[ How might I get this effect without using Javascript or Absolute positioning that wont look proper on all resolution sizes.

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  • SQL Simple ORDER BY

    - by AeroDroid
    I'm new to SQL and I don't think this question should be hard to answer. I have a high-score table for a game that contains the columns name, score, and rank. I want to know how I can order the table by descending order each time a new score is added so the table can always stay ordered by score. I know this is the wrong way of doing this, but I hope this makes my point kind of clearer. UPDATE `HSTable`.`Highscores` ORDER BY `Highscores`.`score` DESC; What is the correct way of approaching this? One more thing, is there a way I can set it so that the ranking value always stays where it's suppose to be from the SQL, for example, 1st place is always at the top regardless the score? Thanks!

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  • Simple File-based Record Storage with Fast Text Searching for Compact Framework and Silverlight

    - by Eric Farr
    I have a single table with lots of records ( 100k) that I need to be able to index and search on several text fields. The easiest searches will have the first part of the string specified (eg, LIKE 'ABC%' in SQL). The tougher searches will need to search for any substring within the text fields (eg, LIKE '%ABC%' in SQL). I need to run on the Compact Framework. SQL Compact is a memory hog and overkill for my one table. Besides, I'd like to be able to run on Silverlight 4 eventually. The file and indexes can be generated on the full .NET Framework and I only need read capability on the Compact Framework. My records are not especially large and can be expressed in fix length format. I'm looking for some existing code or libraries to avoid having to write a file-based BTree implementation from scratch.

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  • Simple Hexadecimal color question

    - by M28
    I have a number between 0.0 and 1.0, I would like to convert it to a grayscale color. White = 0 Black = 1 You can show me how in any understandable language (I prefer actionscript 3) Please, don't just give a name of a function that a language have to do this, I want to know how it does.

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  • C# app running as either Windows Form or as Console Application

    - by Aeolien
    I am looking to have one of my Windows Forms applications be run programmatically—from the command line. In preparation, I have separated the logic in its own class from the Form. Now I am stuck trying to get the application to switch back and forth based on the presence of command line arguments. Here is the code for the main class: static class Program { /// <summary> /// The main entry point for the application. /// </summary> [STAThread] static void Main() { string[] args = Environment.GetCommandLineArgs(); if (args.Length > 1) // gets passed its path, by default { CommandLineWork(args); return; } Application.EnableVisualStyles(); Application.SetCompatibleTextRenderingDefault(false); Application.Run(new Form1()); } private static void CommandLineWork(string[] args) { Console.WriteLine("It works!"); Console.ReadLine(); } where Form1 is my form and the It works! string is just a placeholder for the actual logic. Right now, when running this from within Visual Studio (with command line arguments), the phrase It works! is printed to the Output. However, when running the /bin/Debug/Program.exe file (or /Release for that matter) the application crashes. Am I going about this the right way? Would it make more sense (i.e. take less developer time) to have my logic class be a DLL that gets loaded by two separate applications? Or is there something entirely different that I'm not aware of? Thanks in advance!

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  • Powershell and some simple string manipulation

    - by Pat
    need some help with building a powershell script to help with some basic string manipulation. I know just enough powershell to get in trouble, but can't figure out the syntax or coding to make this work. I have a text file that looks like this - Here is your list of servers: server1 server2.domain.local server3 Total number of servers: 3 I need to take that text file and drop the first and last lines (Always first and last.) Then I need to take every other line and basically turn it into a CSV file. The final output should be a text file that looks like this - server1,server2.domain.local,server3 Any suggestions on where to start? Thanks!

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