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  • C++ Memory Allocation & Linked List Implementation

    - by pws5068
    I'm writing software to simulate the "first-fit" memory allocation schema. Basically, I allocate a large X megabyte chunk of memory and subdivide it into blocks when chunks are requested according to the schema. I'm using a linked list called "node" as a header for each block of memory (so that we can find the next block without tediously looping through every address value. head_ptr = (char*) malloc(total_size + sizeof(node)); if(head_ptr == NULL) return -1; // Malloc Error .. :-( node* head_node = new node; // Build block header head_node->next = NULL; head_node->previous = NULL; // Header points to next block (which doesn't exist yet) memset(head_ptr,head_node, sizeof(node)); ` But this last line returns: error: invalid conversion from 'node*' to 'int' I understand why this is invalid.. but how can I place my node into the pointer location of my newly allocated memory?

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  • Is this a safe/valid hash method implementation?

    - by Sean
    I have a set of classes to represent some objects loaded from a database. There are a couple variations of these objects, so I have a common base class and two subclasses to represent the differences. One of the key fields they have in common is an id field. Unfortunately, the id of an object is not unique across all variations, but within a single variation. What I mean is, a single object of type A could have an id between, say, 0 and 1,000,000. An object of type B could have an id between, 25,000 and 1,025,000. This means there's some overlap of id numbers. The objects are just variations of the same kind of thing, though, so I want to think of them as such in my code. (They were assigned ids from different sets for legacy reasons.) So I have classes like this: @class BaseClass @class TypeAClass : BaseClass @class TypeBClass : BaseClass BaseClass has a method (NSNumber *)objectId. However instances of TypeA and TypeB could have overlapping ids as discussed above, so when it comes to equality and putting these into sets, I cannot just use the id alone to check it. The unique key of these instances is, essentially, (class + objectId). So I figured that I could do this by making the following hash function on the BaseClass: -(NSUInteger)hash { return (NSUInteger)[self class] ^ [self.objectId hash]; } I also implemented isEqual like so: - (BOOL)isEqual:(id)object { return (self == object) || ([object class] == [self class] && [self.objectId isEqual:[object objectId]]); } This seems to be working, but I guess I'm just asking here to make sure I'm not overlooking something - especially with the generation of the hash by using the class pointer in that way. Is this safe or is there a better way to do this?

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  • In the following implementation of static_strlen, why are the & and parentheses around str necessary

    - by Ben
    If I change the type to const char str[Len], I get the following error: error: no matching function for call to ‘static_strlen(const char [5])’ Am I correct that static_strlen expects an array of const char references? My understanding is that arrays are passed as pointers anyway, so what need is there for the elements to be references? Or is that interpretation completely off-the-mark? #include <iostream> template <size_t Len> size_t static_strlen(const char (&str)[Len]) { return Len - 1; } int main() { std::cout << static_strlen("oyez") << std::endl; return 0; }

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  • Pubsub implementation with jaxl library

    - by Pankaj Khurana
    Hi, I am using jaxl library for bot development on my debian server with openfire. Now i want to apply pubsub functionality to it. My scenario is : user subscribes to an event & when an event occurs message is sent to all the subscribers. I am confused how to implement pubsub through im. Please help Thanks

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  • anyone know of a custom membership provider implementation that check password strength against in-b

    - by ronaldwidha
    I've got an Asp.net MVC app and before being able to go live, the IT have requested for us to comply with their password policy. The flexibility of AspnetSqlMembershipProvider doesn’t quite satisfy the requirement. The password strength and length rules are as follows: one lowercase one Uppercase one number and or special character 8 characters in length so far, aspnetsqlmembershipprovider is good... Not allowed to use: Dictionary words Names, real or fictional Plain language phrases Dates Telephone numbers Car registration numbers User IDs Postal codes Organization name Only the first 4 criteria are satisfied by the aspnetsqlmembershipprovider. Do you know of any third party products that offers this functionality (preferably in the form of a custom membership provider)?

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  • TabBar implementation issue in iphone

    - by iPhoneDev
    Hi, My project is navigation based template and it was running fine until I made changes in some child view. I need to add 4 Tab in some child view. So what I did is create a TabBarController programmatically on ViewDidLoad as: // (void)viewDidLoad { [super viewDidLoad]; helpView = [[HelpView alloc] initWithNibName:@"HelpView" bundle:nil]; settingView = [[SettingView alloc] initWithNibName:@"SettingView" bundle:nil]; tabBarController = [[UITabBarController alloc] init]; tabBarController.viewControllers = [NSArray arrayWithObjects:helpView,settingView,nil]; [self.view addSubview:[tabBarController view]]; } I am able to add two view in tab bar but not Tab Title. Please let me know what I am missing to display Title on tab button. ( Is a NavigationBased project) Thanks

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  • DRYing out implementation of ICloneable in several classes

    - by Sarah Vessels
    I have several different classes that I want to be cloneable: GenericRow, GenericRows, ParticularRow, and ParticularRows. There is the following class hierarchy: GenericRow is the parent of ParticularRow, and GenericRows is the parent of ParticularRows. Each class implements ICloneable because I want to be able to create deep copies of instances of each. I find myself writing the exact same code for Clone() in each class: object ICloneable.Clone() { object clone; using (var stream = new MemoryStream()) { var formatter = new BinaryFormatter(); // Serialize this object formatter.Serialize(stream, this); stream.Position = 0; // Deserialize to another object clone = formatter.Deserialize(stream); } return clone; } I then provide a convenience wrapper method, for example in GenericRows: public GenericRows Clone() { return (GenericRows)((ICloneable)this).Clone(); } I am fine with the convenience wrapper methods looking about the same in each class because it's very little code and it does differ from class to class by return type, cast, etc. However, ICloneable.Clone() is identical in all four classes. Can I abstract this somehow so it is only defined in one place? My concern was that if I made some utility class/object extension method, it would not correctly make a deep copy of the particular instance I want copied. Is this a good idea anyway?

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  • C# Property Access vs Interface Implementation

    - by ehdv
    I'm writing a class to represent a Pivot Collection, the root object recognized by Pivot. A Collection has several attributes, a list of facet categories (each represented by a FacetCategory object) and a list of items (each represented by a PivotItem object). Therefore, an extremely simplified Collection reads: public class Collection { private List<FacetCategory> categories; private List<PivotItem> items; // other attributes } What I'm unsure of is how to properly grant access to those two lists. Because declaration order of both facet categories and items is visible to the user, I can't use sets, but the class also shouldn't allow duplicate categories or items. Furthermore, I'd like to make the Collection object as easy to use as possible. So my choices are: Have Collection implement IList<PivotItem> and have accessor methods for FacetCategory: In this case, one would add an item to Collection foo by writing foo.Add(bar). This works, but since a Collection is equally both kinds of list making it only pass as a list for one type (category or item) seems like a subpar solution. Create nested wrapper classes for List (CategoryList and ItemList). This has the advantage of making a consistent interface but the downside is that these properties would no longer be able to serve as lists (because I need to override the non-virtual Add method I have to implement IList rather than subclass List. Implicit casting wouldn't work because that would return the Add method to its normal behavior. Also, for reasons I can't figure out, IList is missing an AddRange method... public class Collection { private class CategoryList: IList<FacetCategory> { // ... } private readonly CategoryList categories = new CategoryList(); private readonly ItemList items = new ItemList(); public CategoryList FacetCategories { get { return categories; } set { categories.Clear(); categories.AddRange(value); } } public ItemList Items { get { return items; } set { items.Clear(); items.AddRange(value); } } } Finally, the third option is to combine options one and two, so that Collection implements IList<PivotItem> and has a property FacetCategories. Question: Which of these three is most appropriate, and why?

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  • Pointer-based binary heap implementation

    - by Derek Chiang
    Is it even possible to implement a binary heap using pointers rather than an array? I have searched around the internet (including SO) and no answer can be found. The main problem here is that, how do you keep track of the last pointer? When you insert X into the heap, you place X at the last pointer and then bubble it up. Now, where does the last pointer point to? And also, what happens when you want to remove the root? You exchange the root with the last element, and then bubble the new root down. Now, how do you know what's the new "last element" that you need when you remove root again?

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  • Program hangs when calling parseFrom for java implementation of protobuf

    - by cornerback84
    I have a message (say its called OuterMessage) message OuterMessage { optional int64 id = 1; optional InnerMessage inner = 2; } and an inner message message InnerMessage { optional string type = 1; optioanl int64 id = 2; } Now when I call parseFrom on OuterMessage like OuterMessage.parseFrom(buffer) the method never returns and nor does it throw any exception. But if I do InnerMessage.parseFrom(buffer) it returns an empty InnerMessage instance. I am serializing the message using protobuf-net. Any idea what might be causing the issue?

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  • I have a generic implementation of PHP mcrypt module and its not decrypting

    - by Ken Mitchner
    class Crypt_Data { protected $_mcrypt=null; protected $_iv=null; protected $_key=null; public function __construct() { $this->_mcrypt = mcrypt_module_open('rijndael_256', '', 'cbc', ''); $key_size = mcrypt_enc_get_key_size($this->_mcrypt); for($i=0;$i<$key_size;$i++) $test_key .= "0"; $this->_iv = $test_key; $this->_key = $test_key; mcrypt_generic_init($this->_mcrypt,$this->_key,$this->_iv); } public function dataEncrypt($data) { return base64_encode(mcrypt_generic($this->_mcrypt, $data)); } public function dataDecrypt($data) { return mdecrypt_generic($this->_mcrypt, base64_decode($data)); } } $crypt = new Crypt_Data(); $string = "encrypt me"; $encrypted = $crypt->dataEncrypt($string); echo $encrypted."<BR>"; $decrypted = $crypt->dataDecrypt($encrypted); echo $decrypted."<BR>"; output: JJKfKxZckkqwfZ5QWeyVR+3PkMQAsP0Gr1hWaygV20I= qÌÌi_ÖZí(®`iÜ¥wÝÿ ô0€Í6Ÿhf[%ër No idea why this isn't working, everything seems to be fine on my end.. i tried decrypting it with mcrypt_cbc(); and it decrypted it properly.. so it has something to do with my mdecrypt_generic.. any ideas?

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  • Best pageable table implementation in GWT

    - by Steve Buikhuizen
    I need to add a paging, sortable table to my GWT application. I see lots of these out there so I'm looking for your experience to save me time by choosing the best one. So far I'm looking at... http://code.google.com/p/gwt-advanced-table/ http://code.google.com/p/google-web-toolkit-incubator/wiki/PagingScrollTableOld I like the second one best. Any stories to tell?

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  • ViewPager and Fragment Pager adapter implementation

    - by Rohit Deshmukh
    So I am trying to implement sliding views/fragments using viewpager and fragment pager adapter. convert_home is my main xml file that has android.support.v4.view.PagerTitleStrip and temperature.xml and velocity.xml are my two other views. I have no clue where I am going wrong. package app.converto; import android.os.Bundle; import android.support.v4.app.Fragment; import android.support.v4.app.FragmentActivity; import android.support.v4.app.FragmentManager; import android.support.v4.app.FragmentPagerAdapter; import android.support.v4.view.ViewPager; import android.view.LayoutInflater; import android.view.Menu; import android.view.View; import android.view.ViewGroup; import android.widget.TextView; public class ConverTo extends FragmentActivity { SectionsPagerAdapter mSectionsPagerAdapter; ViewPager mViewPager; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); mViewPager.setAdapter(mSectionsPagerAdapter); setContentView(R.layout.converto_home); mViewPager = (ViewPager) findViewById(R.id.pager); } @Override public boolean onCreateOptionsMenu(Menu menu) { getMenuInflater().inflate(R.menu.converto_home, menu); return true; } public class SectionsPagerAdapter extends FragmentPagerAdapter { public SectionsPagerAdapter(FragmentManager fm) { super(fm); } @Override public Fragment getItem(int i) { switch(i){ case 0: Fragment1 fragment = new Fragment1(); return fragment; case 1: Fragment2 fragment2 = new Fragment2(); return fragment2; } defaultFragment fragment3 = new defaultFragment(); return fragment3; } @Override public int getCount() { return 2; } // // @Override // public CharSequence getPageTitle(int position) { // switch (position) { // case 0: return getString(R.string.velocity); // case 1: return getString(R.string.temperature); // case 2: return getString(R.string.distance); // } // return null; // } } public static class Fragment1 extends Fragment{ public Fragment1(){ } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { //return inflater.inflate(R.layout.temperature, container, false); View view = inflater.inflate(R.layout.temperature, container, false); TextView textView = (TextView) view.findViewById(R.id.sample); textView.setText(getArguments().getString("title")); return view; } } public static class Fragment2 extends Fragment{ public Fragment2(){ } @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { //return inflater.inflate(R.layout.velocity, container, false); View view = inflater.inflate(R.layout.temperature, container, false); TextView textView = (TextView) view.findViewById(R.id.sample); textView.setText(getArguments().getString("title")); return view; } } public static class defaultFragment extends Fragment{ public defaultFragment(){ }//end constructor @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { // return inflater.inflate(R.layout.temperature, container, false); View view = inflater.inflate(R.layout.temperature, container, false); TextView textView = (TextView) view.findViewById(R.id.sample); textView.setText(getArguments().getString("title")); return view; }//end oncreate }//end default fragment }

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  • C++ option/long option implementation

    - by K Hein
    I am working on a parser for meta programming language using C++ on Linux platform. Right now, I need to implement option/long option for the parser to provide some additional features. Basically, if the user pass in some additional option, the parser needs to store statistics while parsing the text files. I can think of two ways to implement it. One way is to user global to store options entered by users. Another way is to create a singleton class to store options. So I would like to know if there is any other way to implement it. What is the best/most recommended way of implementing it? Thanks in advance. Regards, K.Hein

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  • Event feed implementation - will it scale?

    - by SlappyTheFish
    Situation: I am currently designing a feed system for a social website whereby each user has a feed of their friends' activities. I have two possible methods how to generate the feeds and I would like to ask which is best in terms of ability to scale. Events from all users are collected in one central database table, event_log. Users are paired as friends in the table friends. The RDBMS we are using is MySQL. Standard method: When a user requests their feed page, the system generates the feed by inner joining event_log with friends. The result is then cached and set to timeout after 5 minutes. Scaling is achieved by varying this timeout. Hypothesised method: A task runs in the background and for each new, unprocessed item in event_log, it creates entries in the database table user_feed pairing that event with all of the users who are friends with the user who initiated the event. One table row pairs one event with one user. The problems with the standard method are well known – what if a lot of people's caches expire at the same time? The solution also does not scale well – the brief is for feeds to update as close to real-time as possible The hypothesised solution in my eyes seems much better; all processing is done offline so no user waits for a page to generate and there are no joins so database tables can be sharded across physical machines. However, if a user has 100,000 friends and creates 20 events in one session, then that results in inserting 2,000,000 rows into the database. Question: The question boils down to two points: Is this worst-case scenario mentioned above problematic, i.e. does table size have an impact on MySQL performance and are there any issues with this mass inserting of data for each event? Is there anything else I have missed?

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  • doubt in sizeof implementation

    - by aks
    Below is the program to find the size of a structure without using sizeof operator: struct MyStruct { int i; int j; }; int main() { struct MyStruct *p=0; int size = ((char*)(p+1))-((char*)p); printf("\nSIZE : [%d]\nSIZE : [%d]\n", size); return 0; } My doubt is: Why is typecasting to char * required? If I don't use the char* pointer, the output is 1 - WHY?

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  • MySQL Hashing Function Implementation

    - by Jonas Stevens
    I know that php has md5(), sha1(), and the hash() functions, but I want to create a hash using the MySQL PASSWORD() function. So far, the only way I can think of is to just query the server, but I want a function (preferably in php or Perl) that will do the same thing without querying MySQL at all. For example: MySQL hash - 464bb2cb3cf18b66 MySQL5 hash - *01D01F5CA7CA8BA771E03F4AC55EC73C11EFA229 Thanks!

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  • internal implementation of database Queries

    - by harigm
    In my experience I have used many queries like select, order by, where clause etc.. in mysql, sql-server, oracle etc For a moment i have thought, 1)how is this internally written to implement the above queries 2) which language do they use? 3) is that programming language? if yes which language? 4)what kind of environment required to implement this kind of complex database

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  • What's the recommended implementation for hashing OLE Variants?

    - by Barry Kelly
    OLE Variants, as used by older versions of Visual Basic and pervasively in COM Automation, can store lots of different types: basic types like integers and floats, more complicated types like strings and arrays, and all the way up to IDispatch implementations and pointers in the form of ByRef variants. Variants are also weakly typed: they convert the value to another type without warning depending on which operator you apply and what the current types are of the values passed to the operator. For example, comparing two variants, one containing the integer 1 and another containing the string "1", for equality will return True. So assuming that I'm working with variants at the underlying data level (e.g. VARIANT in C++ or TVarData in Delphi - i.e. the big union of different possible values), how should I hash variants consistently so that they obey the right rules? Rules: Variants that hash unequally should compare as unequal, both in sorting and direct equality Variants that compare as equal for both sorting and direct equality should hash as equal It's OK if I have to use different sorting and direct comparison rules in order to make the hashing fit. The way I'm currently working is I'm normalizing the variants to strings (if they fit), and treating them as strings, otherwise I'm working with the variant data as if it was an opaque blob, and hashing and comparing its raw bytes. That has some limitations, of course: numbers 1..10 sort as [1, 10, 2, ... 9] etc. This is mildly annoying, but it is consistent and it is very little work. However, I do wonder if there is an accepted practice for this problem.

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  • Is this implementation truely tail-recursive?

    - by CFP
    Hello everyone! I've come up with the following code to compute in a tail-recursive way the result of an expression such as 3 4 * 1 + cos 8 * (aka 8*cos(1+(3*4))) The code is in OCaml. I'm using a list refto emulate a stack. type token = Num of float | Fun of (float->float) | Op of (float->float->float);; let pop l = let top = (List.hd !l) in l := List.tl (!l); top;; let push x l = l := (x::!l);; let empty l = (l = []);; let pile = ref [];; let eval data = let stack = ref data in let rec _eval cont = match (pop stack) with | Num(n) -> cont n; | Fun(f) -> _eval (fun x -> cont (f x)); | Op(op) -> _eval (fun x -> cont (op x (_eval (fun y->y)))); in _eval (fun x->x) ;; eval [Fun(fun x -> x**2.); Op(fun x y -> x+.y); Num(1.); Num(3.)];; I've used continuations to ensure tail-recursion, but since my stack implements some sort of a tree, and therefore provides quite a bad interface to what should be handled as a disjoint union type, the call to my function to evaluate the left branch with an identity continuation somehow irks a little. Yet it's working perfectly, but I have the feeling than in calling the _eval (fun y->y) bit, there must be something wrong happening, since it doesn't seem that this call can replace the previous one in the stack structure... Am I misunderstanding something here? I mean, I understand that with only the first call to _eval there wouldn't be any problem optimizing the calls, but here it seems to me that evaluation the _eval (fun y->y) will require to be stacked up, and therefore will fill the stack, possibly leading to an overflow... Thanks!

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  • Drag and drop an image from desktop to a web text editor (implementation in javascript)

    - by fatmatto
    I tried to write reasonably short title but i failed i guess.. Hi everybody here's what i'm trying to do: I want to implement a web text editor able to recognize when the user drag a image file over it's editing surface and it automa(gically) starts the upload and insert the image near the cursor position. In other words i don't want the user to do the usual "insert-image-browse-ok". Atm i am not very good at javascript ... i know JQuery but i have not a clear idea about how to implement this... i don't know if there's an event handler able to help me in this situation... if not then there should be i think or web apps would miss some kind of interactivity. I've heard miracles about HTML5 could it help me? I've seen such things in Google Wave but that surface doesn't seem to be a form field... google lab's black magic i guess.... Thank you in advance.

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