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• What grid distributed computing frameworks are currently favoured for trading systems

  - by Rich

  There seems to a quite a few grid computing frameworks out there, but which ones are actually being used to any great extent by the investment banks for purposes of low latency distributing calculation? I'd be interested to hear answers covering both windows,Linux and cross platform. Also, what RPC mechanisms seem to be favoured most? I've heard that for reason of low latency and speed, the calculations themselves are quite often written in C++/C as calculations running on VMs are several orders of magnitude slower than native code. Does this seem to be a common scenario in practice? e.g distributed .NET grid framework running calculations written in native c++/c?

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• Import Data from text file into sql DB using CSLA

  - by New Developer

  I am trying to import data from ~ Delimited Text file into SQL Server using CSLA. My text file has 92,000 records in it. Here are the issues i am having with the import When i create a BusinnessListBase .new and add all my records to it, it gives me a "Out of meory exception". So to fix it i create a new bussinessbase object and save it. this works fine and is much faster too. It takes 15 minutes I have to run my program again and check for any changes and hence update them, this is where it takes too much time. Is there any alternative way to speed up my import?

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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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• typedef declaration syntax

  - by mt_serg

  Some days ago I looked at boost sources and found interesting typedef. There is a code from "boost\detail\none_t.hpp": namespace boost { namespace detail { struct none_helper{}; typedef int none_helper::*none_t ; } // namespace detail } // namespace boost I didn't see syntax like that earlier and can't explain the sense of that. This typedef introduces name "none_t" as pointer to int in boost::detail namespace. What the syntax is? And what difference between "typedef int none_helper::*none_t" and for example "typedef int *none_t" ?

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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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• File in binary form

  - by Abhi

  Dear All I want to write data into the file in binary form. I was trying using the mentioned below FILE *fp = fopen("binaryoutput.rgb888", "ab+"); for(int m=0; m<height; m++) { for (int n=0; n< width; n++) { temp = (pOutputImg+m*3+n*3); // here temp is a pointer to a unsigned char fprintf(fp,"%u",*temp); } } fclose(fp); I am able to get data which is strored at pOutputImg but not in binary form. Can anyone guide me the correct step.. Thanks in advance

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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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• 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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• Cannot implicitly convert type 'char*' to 'bool'

  - by neeraj

  i was trying to passing pointer value in the function , i really got stuck here I am a beginner , not getting what value should be put this is programme from the reference of the book "Cracking the coding interview " By Gayle Laakmann McDowell, class Program { unsafe void reverse(char *str) { char* end = str; char tmp; if (str) //Cannot implicitly convert type 'char*' to 'bool' { while(*end) //Cannot implicitly convert type 'char*' to 'bool' { ++end; } --end; while(str<end) { tmp = *str; *str+= *end; *end-= tmp; } } } public static void Main(string[] args) { } }

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• Which is quicker? Memcache or file query? (using maxmind geoip.dat file)

  - by tomcritchlow

  Hi, I'm using Python on Appengine and am looking up the geolocation of an IP address like this: import pygeoip gi = pygeoip.GeoIP('GeoIP.dat') Location = gi.country_code_by_addr(self.request.remote_addr) (pygeoip can be found here: http://code.google.com/p/pygeoip/) I want to geolocate each page of my app for a user so currently I lookup the IP address once then store it in memcache. My question - which is quicker? Looking up the IP address each time from the .dat file or fetching it from memcache? Are there any other pros/cons I need to be aware of? For general queries like this, is there a good guide to teach me how to optimise my code and run speed tests myself? I'm new to python and coding in general so apologies if this is a basic concept. Thanks! Tom

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• Objective-C: Initializing char with char at index of string.

  - by Mr. McPepperNuts

  unichar myChar = [myString characterAtIndex:0]; [myNSMutableArray addObject:myChar]; I am trying to insert the first char of a string into an array, to create an array of chars. the first line does not give me an error. The second line however, provides the following error: warning: passing argument 1 of 'addObject:' makes pointer from integer without a cast This also crashes the application with a "bad address" error. I thought this error was due to a problem with memory allocation. Can someone shed some light on this.

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• Are raw C++ pointers first class objects?

  - by Shailesh Kumar

  According to Wikipedia: An object is first-class when it: can be stored in variables and data structures can be passed as a parameter to a subroutine can be returned as the result of a subroutine can be constructed at runtime has intrinsic identity (independent of any given name) Somebody had once told me that raw pointers are not first class objects while smart pointers like std::auto_ptr are. But to me, a raw pointer (to an object or to a function) in C++ does seem to me to satisfy the conditions stated above to qualify as a first class object. Am I missing something?

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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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• Apache server-side files caching via .htaccess?

  - by purpler

  Hi, I'm starting new website and gonna include several JS libs and would like to know how .htaccess file template should look like with caching of media and JS files on? Whats better for compression, GZip or Deflate? Is it better/faster solution to serve those JS libs of the Google CDN perhaps then locally? I'm asking CDN question since some of scripts served off GoogleCDN are potentially going to update and eventually break the website layout so i thought it would be better for me to host them locally and cache via webserver if its going to work with same/near-same speed.

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• OpenGL texture not showing up on some computers, problem with auxDIBImageLoad?

  - by CptanPanic

  I have a simple openGL GUI that has uses a bmp as a texture. The problem is on some computers the texture doesn't show up. But on ones with newer OpenGL drivers it works. How can I make it more compatible. I think the problem may be with auxDIBImageLoad. When I inspect the result, I see the x,y correct, but the data pointer points to memory bank with all zeros. What could be wrong?

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• What is an efficient way to erase substrings?

  - by Legend

  I have a long string and a set of <end-index, string> list like the following: long_sentence = "This is a long long long long sentence" indices = [[6, "is"], [8, "is a"], [18, "long"], [23, "long"]] An element 6, "is" indicates that 6 is the end index of the word "is" in the string. I want to get the following string in the end: >> print long_sentence This .... long ......... long sentence" I tried an approach like this: temp = long_sentence for i in indices: temp = temp[:int(i[0]) - len(i[1])] + '.'*(len(i[1])+1) + temp[i[0]+1:] While this seems to be working, it is taking exceptionally long time (more than 6 hours on 5000 strings inside a 300 MB file). Is there a way to speed this up?

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• Extract anything that looks like links from large amount of data in python

  - by Riz

  Hi, I have around 5 GB of html data which I want to process to find links to a set of websites and perform some additional filtering. Right now I use simple regexp for each site and iterate over them, searching for matches. In my case links can be outside of "a" tags and be not well formed in many ways(like "\n" in the middle of link) so I try to grab as much "links" as I can and check them later in other scripts(so no BeatifulSoup\lxml\etc). The problem is that my script is pretty slow, so I am thinking about any ways to speed it up. I am writing a set of test to check different approaches, but hope to get some advices :) Right now I am thinking about getting all links without filtering first(maybe using C module or standalone app, which doesn't use regexp but simple search to get start and end of every link) and then using regexp to match ones I need.

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• High level programming logic, design, pattern

  - by Muhammad Shahzad

  I have been doing programming from last 7 years, getting better and better, but still i think that am lacking something. I have been doing work in JOOMLA, MAGENTO, WP, Custom PHP, Opencart, laravel, codeignitor. Sometimes i need to design logic for a huge database application, in the applications we need nesting loops and queries, although i follow OOPS standards, ORM etc, still i feel i need more robust coding designs. I need to know how can i improve these things, so that code remain neat, efficient and faster. Also how big webapps like facebook twitter tests there code speed? How high level programmers choose design patterns. If you can help me find something useful with examples?

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• C optimization breaks algorithm

  - by Halpo

  I am programming an algorithm that contains 4 nested for loops. The problem is at at each level a pointer is updated. The innermost loop only uses 1 of the pointers. The algorithm does a complicated count. When I include a debugging statement that logs the combination of the indexes and the results of the count I get the correct answer. When the debugging statement is omitted, the count is incorrect. The program is compiled with the -O3 option on gcc. Why would this happen?

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• Why doesn't Perl threading work when I call readdir beforehand?

  - by Kevin

  Whenever I call readdir before I create a thread, I get an error that looks like this: perl(2820,0x7fff70c33ca0) malloc: * error for object 0x10082e600: pointer being freed was not allocated * set a breakpoint in malloc_error_break to debug Abort trap What's strange is that it happens when I call readdir before I create a thread (i.e. readdir is not called in any concurrent code). I don't even use the results from readdir, just making the call to it seems to screw things up. When I get rid of it, things seem to work fine. Some example code is below: opendir(DIR, $someDir); my @allFiles = readdir(DIR); close(DIR); my $thread = threads-create(\&sub1); $thread-join(); sub sub1 { print "in thread\n" }

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• c++/cli pass (managed) delegate to unmanaged code

  - by Ron Klein

  How do I pass a function pointer from managed C++ (C++/CLI) to an unmanaged method? I read a few articles, like this one from MSDN, but it describes two different assemblies, while I want only one. Here is my code: 1) Header (MyInterop.ManagedCppLib.h): #pragma once using namespace System; namespace MyInterop { namespace ManagedCppLib { public ref class MyManagedClass { public: void DoSomething(); }; }} 2) CPP Code (MyInterop.ManagedCppLib.cpp) #include "stdafx.h" #include "MyInterop.ManagedCppLib.h" #pragma unmanaged void UnmanagedMethod(int a, int b, void (*sum)(const int)) { int result = a + b; sum(result); } #pragma managed void MyInterop::ManagedCppLib::MyManagedClass::DoSomething() { System::Console::WriteLine("hello from managed C++"); UnmanagedMethod(3, 7, /* ANY IDEA??? */); } I tried creating my managed delegate and then I tried to use Marshal::GetFunctionPointerForDelegate method, but I couldn't compile.

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• Grid view update event form javascript

  - by pranay

  I have grid control select <%--Select--% </ItemTemplate> </asp:TemplateField> </columns> <pagersettings mode="NumericFirstLast" position="Top" pagebuttoncount="5" /> <pagerstyle backcolor="Pink" /> </cc:AppEngineGridView> my code on row create protected override void OnRowCreated(GridViewRowEventArgs e) { try { if (e.Row.RowType == DataControlRowType.DataRow) { e.Row.ID = this.ID + "_" + e.Row.RowIndex; e.Row.Attributes.Add("onmouseover", "this.style.cursor='pointer';this.style.font.weight='bolder';"); e.Row.Attributes.Add("onclick", "DoNav('" + ((LinkButton)e.Row.FindControl("lbtn1")).ClientID + "');"); } } protected void grduser_RowUpdating(object sender, GridViewUpdateEventArgs e) { grdview_RowClickCommand(sender, e); } Javascript : function DoNav(id) { $("#"+id).click(); } Now my question is when i click on the row it do post back but it didnt call rowupdate event How can do this i.e using javascript to call row update command of the grid.

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• Resources for memory management in embedded application

  - by Elazar Leibovich

  How should I manage memory in my mission critical embedded application? I found some articles with google, but couldn't pinpoint a really useful practical guide. The DO-178b forbids dynamic memory allocations, but how will you manage the memory than? preallocate everything in advance and send a pointer to each function that needs allocation? Allocate it on the stack? Use a global static allocator (but then it's very similar to dynamic allocation)? Answers can be of the form of regular answer, reference to a resource, or reference to good opensource embedded system for example. clarification: The issue here is not whether or not memory management is availible for the embedded system. But what is a good design for an embedded system, to maximize reliability.

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• Scalable (half-million files) version control system

  - by hashable

  We use SVN for our source-code revision control and are experimenting using it for non-source-code files. We are working with a large set (300-500k) of short (1-4kB) text files that will be updated on a regular basis and need to version control it. We tried using SVN in flat-file mode and it is struggling to handle the first commit (500k files checked in) taking about 36 hours. On a daily basis, we need the system to be able to handle 10k modified files per commit transaction in a short time (<5 min). My questions: Is SVN the right solution for my purpose. The initial speed seems too slow for practical use. If Yes, is there a particular svn server implementation that is fast? (We are currently using the gnu/linux default svn server and command line client.) If No, what are the best f/oss/commercial alternatives Thanks

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• How to change input button image using CSS?

  - by Baltimark

  So, I can create an input button with an image using <INPUT type="image" src="/images/Btn.PNG" value=""> But, I can't get the same behavior using CSS. for instance, i've tried <INPUT type="image" class="myButton" value=""> where "myButton" is defined in the css file as .myButton{ background:url(/images/Btn.PNG) no-repeat; cursor:pointer; width: 200px; height: 100px; border: none; } If that's all I wanted to do, I could use the original style, but I want to change the button's appearance on hover (using a myButton:hover class). I know the links are good because I've been able to load them for a background image for other parts of the page (just as a check). I found examples on the web of how to do it using javascript, but I'm looking for a css solution. I'm using Firefox 3.0.3 if that makes a difference. Thanks

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