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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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• Confused about "override" vs. "new" in C#

  - by iTayb

  I'm having the following classes: class Base { public virtual void Print() { Console.WriteLine("Base"); } } class Der1 : Base { public new virtual void Print() { Console.WriteLine("Der1"); } } class Der2 : Der1 { public override void Print() { Console.WriteLine("Der2"); } } This is my main method: Base b = new Der2(); Der1 d1 = new Der2(); Der2 d2 = new Der2(); b.Print(); d1.Print(); d2.Print(); The output is Base, Der2, Der2. As far as I know, Override won't let previous method to run, even if the pointer is pointing to them. So the first line should output Der2 as well. However Base came out. How is it possible? How the override didn't work there?

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• Using multiple databases within one application

  - by Alex

  I have a web application made for several groups of people not connected with each other. Instead of using one database for all of them, I'm thinking about making separate databases. This will improve the speed of the queries and make me free from checking to what group the user belongs. But since I'm working with LINQ to SQL, my classes are explicitly connected with the databases, so I will have to make separate DataContexts for all of the databases. So how can I solve this problem? Or should I just not bother and use one database only?

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• Array of char *

  - by user353060

  Hello, I am having problems with array pointers. I've looked through Google and my attempts are futile so far. What I would like to do is, I have a char name[256]. I will be 10 of those. Hence, I would need to keep track of each of them by pointers. Trying to create a pointer to them. int main() { char superman[256] = "superman"; char batman[256] = "batman"; char catman[256] = "catman"; char *names[10]; names[0] = superman; names[1] = batman; system("pause"); return 0; } How do I actually traverse an array of pointers?

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• Objective C LValue required as unary '&' operand

  - by Bob

  Hello! In my code, I get this error when I try to get a pointer to my class property. (I wrote a small *.OBJ file translator in Python, discarding the normals) CODE: //line: line of text const char *str = [line UTF8String]; Point3D *p1, *p2, *p3; p1 = [Point3D makeX:0 Y:0 Z:0]; p2 = [Point3D makeX:0 Y:0 Z:0]; p3 = [Point3D makeX:0 Y:0 Z:0]; sscanf(str, "t %f,%f,%f %f,%f,%f %f,%f,%f",(&[p1 x]),&([p1 y]),&([p1 z]),&([p2 x]),&([p2 y]),&([p2 z]),&([p3 x]),&([p3 y]),&([p3 z])); Triangle3D *tri = [Triangle3D make:p1 p2:p2 p3:p3];

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• How to convert from integer to unsigned char in C, given integers larger than 256?

  - by Alf_InPogform

  As part of my CS course I've been given some functions to use. One of these functions takes a pointer to unsigned chars to write some data to a file (I have to use this function, so I can't just make my own purpose built function that works differently BTW). I need to write an array of integers whose values can be up to 4095 using this function (that only takes unsigned chars). However am I right in thinking that an unsigned char can only have a max value of 256 because it is 1 byte long? I therefore need to use 4 unsigned chars for every integer? But casting doesn't seem to work with larger values for the integer. Does anyone have any idea how best to convert an array of integers to unsigned chars?

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• Measure CPU performance via JS

  - by Nicholas Kyriakides

  A webapp has as a central component a relatively heavy algorithm that handles geometric operations. There are 2 solutions to make the whole thing accessible from both high-end machines and relatively slower mobile devices. I will use RPC's if i detect that the user machine is ''slow'' or else if i detect that the user machine can handle it OK, then i provide to the webapp the script to handle it client side. Now what would be a reliable way to detect the speed of the user machine? I was thinking of providing a sample script as a test when the page loads and detect the time it took to execute that. Any ideas?

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• How to stream a WAV file?

  - by jonasb

  I'm writing an app where I record audio and upload the audio file over the web. In order to speed up the upload I want to start uploading before I've finished recording. The file I'm creating is a WAV file. My plan was to use multiple data chunks. So instead of the normal encoding (RIFF, fmt , data) I’m using (RIFF, fmt , data, data, ..., data). The first issue is that the RIFF header wants the total length of the whole file, but that is of course not known when streaming the audio (I’m now using an arbitrary number). The other problem is that I'm not sure if it's valid since Audacity doesn't recognise the file, and Windows Media Player opens the file but plays only a very small part. I've been reading WAV specs but haven’t found an answer. Any suggestions?

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• Is it possible to generate plain-old XML using Haml?

  - by lsdr

  I've been working on a piece of software where I need to generate a custom XML file to send back to a client application. The current solutions on Ruby/Rails world for generating XML files are slow, at best. Using builder or event Nokogiri, while have a nice syntax and are maintainable solutions, they consume too much time and processing. I definetly could go to ERB, which provides a good speed at the expense of building the whole XML by hand. HAML is a great tool, have a nice and straight-forward syntax and is fairly fast. But I'm struggling to build pure XML files using it. Which makes me wonder, is it possible at all? Does any one have some pointers to some code or docs showing how to do this, build a full, valid XML from HAML?

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• Is there a leak in this copy code?

  - by Don Wilson

  Is there a leak in this code? // Move the group Group *movedGroup = [[Group alloc] init]; movedGroup = [[[[GroupList sharedGroupList] groups] objectAtIndex:fromIndex] copy]; [[GroupList sharedGroupList] deleteGroup:fromIndex]; [[GroupList sharedGroupList] insertGroup:movedGroup atIndex:toIndex]; // Update the loadedGroupIndex pointer if (loadedGroupIndex < fromIndex & loadedGroupIndex >= toIndex) { loadedGroupIndex = loadedGroupIndex + 1; } else if (loadedGroupIndex > fromIndex & loadedGroupIndex < toIndex) { loadedGroupIndex = loadedGroupIndex - 1; } else if (loadedGroupIndex == fromIndex) { loadedGroupIndex = toIndex; } [movedGroup release]

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• Reading in 4 bytes at a time

  - by alphomega

  I have a big file full of integers that I'm loading in. I've just started using C++, and I'm trying out the filestream stuff. From everything I've read, it appears I can only read in bytes, So I've had to set up a char array, and then cast it as a int pointer. Is there a way I can read in 4 bytes at a time, and eliminate the need for the char array? const int HRSIZE = 129951336; //The size of the table char bhr[HRSIZE]; //The table int *dwhr; int main() { ifstream fstr; /* load the handranks.dat file */ std::cout << "Loading table.dat...\n"; fstr.open("table.dat"); fstr.read(bhr, HRSIZE); fstr.close(); dwhr = (int *) bhr; }

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• Drupal: Programmatically saving imagefield images

  - by Ace

  Hey there! I'm trying to write a sync function that saves some data to nodes, which works fine, until I try to save the thumbnail image associated with the node. I've managed to download the file and put it in my sites/default/files folder, but what's the best way to tell Drupal, "put this file in that CCK imagefield"? EDIT To clarify a bit.. I sync the thumbnails separately (since one image can be used by several nodes)... I would like the initial thumbnail sync to save the files in the correct folder (not a temp one) and just point the imagefield to this file... That's what annoys me with field_file_save_file(), it saves a new file instead of just making a pointer.. Any advice?

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• If free() knows the length of my array, why can't I ask for it in my own code?

  - by Chris Cooper

  I know that it's a common convention to pass the length of dynamically allocated arrays to functions that manipulate them: void initializeAndFree(int* anArray, int length); int main(){ int arrayLength = 0; scanf("%d", &arrayLength); int* myArray = (int*)malloc(sizeof(int)*arrayLength); initializeAndFree(myArray, arrayLength); } void initializeAndFree(int* anArray, int length){ int i = 0; for (i = 0; i < length; i++) { anArray[i] = 0; } free(anArray); } but if there's no way for me to get the length of the allocated memory from a pointer, how does free() "automagically" know what to deallocate? Why can't I get in on the magic, as a C programmer? Where does free() get its free (har-har) knowledge from?

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• jQuery click event not working when mouse moves from one div to another with button held down

  - by Acorn

  I've made a page that uses jQuery to allow you to place <div>s on the page based on your mouse coordinates when you click. The page And here's the javascript: $('document').ready(function() { $("#canvas").click(function(e){ var x = e.pageX - this.offsetLeft; var y = e.pageY - this.offsetTop; $(document.createElement('div')).css({'left':x + 'px', 'top':y + 'px'}).addClass('tile').appendTo('#canvas'); }); }); I've found that if you mousedown in the div#canvas and mouseup with your pointer over a placed <div> (or vice versa) then a new <div> doesn't get placed. Why is this?

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• Why are the interpreters of all popular scripting languages written in C (if not in C at least not i

  - by wndsr

  I recently asked a question on switching from C++ to C for writing an interpreter for speed and I got a comment from someone asking why on earth I would switch to C for that. So I found out that I actually don't know why - except that C++ object oriented system has a much higher abstraction and therefore is slower. Why are the interpreters of all popular scripting languages written in C and not in C++? If you want to tell me about some other language where the interpreter for it isn't in C, please replace all occurences of popular scripting languages in this question with Ruby, Python, Perl and PHP.

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• str_replace() with two-dimensional array

  - by Qiao

  You can use arrays with str_replace(): $array_from = array ('from1', 'from2'); $array_to = array ('to1', 'to2'); $text = str_replace ($array_from, $array_to, $text); But what if you have two-dimensional array? $array_from_to = array ( 'from1' => 'to1'; 'from2' => 'to2'; ); How can you use it with str_replace()? Speed matters - array is big enough.

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• How do I connect two apps

  - by sevaxx

  I am considering building an app in C++ that will be parsing text from the web and create some statistical results. These results I want to be fed in an external app in real time. The external app (to whose code I have no access, but can ask for a - paid - custom made addition) will then need some code to read and use these results. I am wondering what would be the best way to interconnect the two apps, in terms of speed and ease of implementation. I am considering : disk I/O (slow) a Windows service a DLL a web service a web page Perhaps I am missing a better solution ? Thank you.

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• Handle/Grip bar convention

  - by tomdemuyt

  Greetings, Because textarea elements do not resize with jquery.touch ( http://plugins.jquery.com/project/touch ), I've put an textarea in a table where the first row allows the user to drag the table around and resize it with the textarea growing/shrinking/moving along. It works well, except that users dont seem to 'get' that they can use the bar to resize/move. I was trying to find some 'grip bar' graphics but google isnt helping me. What is the best way to show users that an element can be moved/resized ? Pointer to graphics ( generators ) would be great. Or, does any one know how to make textarea's movable/resizable ? T.

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• Indexing datetime in MySQL

  - by User1

  What is the best way to index a datetime in MySQL? Which method is faster: Store the datetime as a double (via unix timestamp) Store the datetime as a datetime The application generating the timestamp data can output either format. Unfortunately, datetime will be a key for this particular data structure so speed will matter. Also, is it possible to make an index on an expression? For example, index on UNIX_TIMESTAMP(mydate) where mydate is a field in a table and UNIX_TIMESTAMP is a mysql function. I know that Postgres can do it. I'm thinking there must be a way in mysql as well.

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• migrating C++ code from structures to classes

  - by eSKay

  I am migrating some C++ code from structures to classes. I was using structures mainly for bit-field optimizations which I do not need any more (I am more worried about speed than saving space now). What are the general guidelines for doing this migration? I am still in the planning stage as this is a very big move affecting a major part of the code. I want to plan everything first before doing it. What are all the essential things I should keep in mind?

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• Resources for learning how to better read code

  - by rsteckly

  Hi, I recently inherited a large codebase and am having to read it. The thing is, I've usually been the dev starting a project. As a result, I don't have a lot of experience reading code. My reaction to having to read a lot of code is, well, umm to rewrite it. But I need to bring myself up to speed quickly and build on top of an existing system. Do other people have techniques they've learned to absorb a code base? At this point, I'm just reading through the code. I've tried generating UML diagrams using UModel. They're so big they won't print cleanly and when I zoom in, I really do lose the perspective of seeing all the relationships. How have other people dealt with this problem?

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• jquery mouseleave issue when moving too slow

  - by David

  Hello. I am using the jQuery mouseenter and mouseleave events to slide a div down and up. Everything works well except for the mouseleave which doesn't appear to fire ONLY if the mouse of moved off of the div quite slowly. If i move the mouse at a relatively normal or fast speed then it works as expected. Can anyone explain this or provide any info on how to get around this? Code: $(document).ready(function() { $('header').mouseenter(function() { $(this).stop().animate({'top' : '25px'}, 500, function() { $(this).delay(600).animate({'top' : '-50px'}, 500); }); }). mouseleave(function(e) { var position = $(this).position(); if (e.pageY > position.top + $(this).height()) { $(this).stop().delay(600).animate({'top' : '-75px'}, 500) ; } }); });

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• jQuery .submit() woes with IE8

  - by Jitesh

  I am trying to submit a delete link click via a http post to my asp.net mvc controller. While my code below works for chrome it does not work in IE8. Any pointer will be very useful. Setup:- Browser: IE8 jQuery: 1.4.1 MVC: 2.0 The delete link is:- <a title="Delete contact" href="/Contacts/Delete/<%= Model.Contact.Id %>" class="delete" rel="Are you sure you want to delete <%= Html.Encode(Model.Contact.Name) %>?">Delete</a> and the jqeury handler for the click of delete is $("a.delete").click(function() { if (confirm($(this).attr("rel"))) { var form = "<form method='POST' action='" + $(this).attr("href") + '" style='display:none;'></form>"; $(form).submit(); } return false; });

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• A programming language for teaching data structures and algorithms with? [closed]

  - by Andreas Grech

  Possible Duplicate: Choice of programming language for learning data structures and algorithms Teachers have different opinions on what programming language they would choose to teach data structures and algorithms with. Some would prefer a lower level language such as C because it allows the student to learn more about what goes on beyond the abstractions in terms of memory allocation and deallocation and pointers and pointer arithmetic. On the other hand, others would say that they would prefer a higher level language like Java because it allows the student to learn more about the concepts of the structures and the algorithm design rather than 'waste time' and fiddle around with memory segmentation faults and all the blunders that come with languages where memory management is manual. What is your take on this issue? And also, please post any references you may know of that also discuss this argument.

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• Marshalling a C structure to C#

  - by Hilbert

  Hi, I don't know how to marshall this structure in Mono. typedef struct rib_struct { rib_used_t used; rib_status_t status; rib_role_t role; uint8_t conf; rib_dc_t *pending; pthread_mutex_t mutex; pthread_cond_t cond; rib_f_t *props; } rib_t; And for example, rib_dc_t is like: typedef struct rib_dc_struct { uint16_t id; uint8_t min_id; uint8_t conf; struct rib_dc_struct *next; } rib_dc_t; I don't know how to marshall the pthread structures. And the pointers... should I use IntPtr or a managed structures? How to mashall the pointer in the last struct to the struct itself? Thanks in adanvaced

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