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  • Automatically update php loop with data pulled from database

    - by John Svensson
    SQL STRUCTURE CREATE TABLE IF NOT EXISTS `map` ( `id` int(11) NOT NULL AUTO_INCREMENT, `x` int(11) NOT NULL, `y` int(11) NOT NULL, `type` varchar(50) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=3 ; http://localhost/map.php?x=0&y=0 When I update the x and y via POST or GET, I would like to pull the new data from the database without refreshing the site, how would I manage that? Could someone give me some examples, because I am really stuck here. <?php mysql_connect('localhost', 'root', ''); mysql_select_db('hol'); $startX = $_GET['x']; $startY = $_GET['y']; $fieldHeight = 6; $fieldWidth = 6; $sql = "SELECT id, x, y, type FROM map WHERE x BETWEEN ".$startX." AND ".($startX+$fieldWidth). " AND y BETWEEN ".$startY." AND ".($startY+$fieldHeight); $result = mysql_query($sql); $positions = array(); while ($row = mysql_fetch_assoc($result)) { $positions[$row['x']][$row['y']] = $row; } echo "<table>"; for($y=$startY; $y<$startY+$fieldHeight; $y++) { echo "<tr>"; for($x=$startX; $x<$startX+$fieldWidth; $x++) { echo "<td>"; if(isset($positions[$x][$y])) { echo $positions[$x][$y]['type']; } else { echo "(".$x.",".$y.")"; } echo "</td>"; } echo "</tr>"; } echo "</table>"; ?>

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  • How does Haskell do pattern matching without us defining an Eq on our data types?

    - by devoured elysium
    I have defined a binary tree: data Tree = Null | Node Tree Int Tree and have implemented a function that'll yield the sum of the values of all its nodes: sumOfValues :: Tree -> Int sumOfValues Null = 0 sumOfValues (Node Null v Null) = v sumOfValues (Node Null v t2) = v + (sumOfValues t2) sumOfValues (Node t1 v Null) = v + (sumOfValues t1) sumOfValues (Node t1 v t2) = v + (sumOfValues t1) + (sumOfValues t2) It works as expected. I had the idea of also trying to implement it using guards: sumOfValues2 :: Tree -> Int sumOfValues2 Null = 0 sumOfValues2 (Node t1 v t2) | t1 == Null && t2 == Null = v | t1 == Null = v + (sumOfValues2 t2) | t2 == Null = v + (sumOfValues2 t1) | otherwise = v + (sumOfValues2 t1) + (sumOfValues2 t2) but this one doesn't work because I haven't implemented Eq, I believe: No instance for (Eq Tree) arising from a use of `==' at zzz3.hs:13:3-12 Possible fix: add an instance declaration for (Eq Tree) In the first argument of `(&&)', namely `t1 == Null' In the expression: t1 == Null && t2 == Null In a stmt of a pattern guard for the definition of `sumOfValues2': t1 == Null && t2 == Null The question that has to be made, then, is how can Haskell make pattern matching without knowing when a passed argument matches, without resorting to Eq?

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  • Looping through a method without for/foreach/while

    - by RichK
    Is there a way of calling a method/lines of code multiple times not using a for/foreach/while loop? For example, if I were to use to for loop: int numberOfIterations = 6; for(int i = 0; i < numberOfIterations; i++) { DoSomething(); SomeProperty = true; } The lines of code I'm calling don't use 'i' and in my opinion the whole loop declaration hides what I'm trying to do. This is the same for a foreach. I was wondering if there's a looping statement I can use that looks something like: do(6) { DoSomething(); SomeProperty = true; } It's really clear that I just want to execute that code 6 times and there's no noise involving index instantiating and adding 1 to some arbitrary variable. As a learning exercise I have written a static class and method: Do.Multiple(int iterations, Action action) Which works but scores very highly on the pretentious scale and I'm sure my peers wouldn't approve. I'm probably just being picky and a for loop is certainly the most recognisable, but as a learning point I was just wondering if there (cleaner) alternatives. Thanks. (I've had a look at this thread, but it's not quite the same) http://stackoverflow.com/questions/2248985/using-ienumerable-without-foreach-loop

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  • SQL: find entries in 1:n relation that don't comply with condition spanning multiple rows

    - by milianw
    I'm trying to optimize SQL queries in Akonadi and came across the following problem that is apparently not easy to solve with SQL, at least for me: Assume the following table structure (should work in SQLite, PostgreSQL, MySQL): CREATE TABLE a ( a_id INT PRIMARY KEY ); INSERT INTO a (a_id) VALUES (1), (2), (3), (4); CREATE TABLE b ( b_id INT PRIMARY KEY, a_id INT, name VARCHAR(255) NOT NULL ); INSERT INTO b (b_id, a_id, name) VALUES (1, 1, 'foo'), (2, 1, 'bar'), (3, 1, 'asdf'), (4, 2, 'foo'), (5, 2, 'bar'), (6, 3, 'foo'); Now my problem is to find entries in a that are missing name entries in table b. E.g. I need to make sure each entry in a has at least the name entries "foo" and "bar" in table b. Hence the query should return something similar to: a_id = 3 is missing name "bar" a_id = 4 is missing name "foo" and "bar" Since both tables are potentially huge in Akonadi, performance is of utmost importance. One solution in MySQL would be: SELECT a.a_id, CONCAT('|', GROUP_CONCAT(name ORDER BY NAME ASC SEPARATOR '|'), '|') as names FROM a LEFT JOIN b USING( a_id ) GROUP BY a.a_id HAVING names IS NULL OR names NOT LIKE '%|bar|foo|%'; I have yet to measure the performance tomorrow, but severly doubt it's any fast for tens of thousand of entries in a and thrice as many in b. Furthermore we want to support SQLite and PostgreSQL where to my knowledge the GROUP_CONCAT function is not available. Thanks, good night.

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  • cuda 5.0 namespaces for contant memory variable usage

    - by Psypher
    In my program I want to use a structure containing constant variables and keep it on device all long as the program executes to completion. I have several header files containing the declaration of 'global' functions and their respective '.cu' files for their definitions. I kept this scheme because it helps me contain similar code in one place. e.g. all the 'device' functions required to complete 'KERNEL_1' are separated from those 'device' functions required to complete 'KERNEL_2' along with kernels definitions. I had no problems with this scheme during compilation and linking. Until I encountered constant variables. I want to use the same constant variable through all kernels and device functions but it doesn't seem to work. ########################################################################## CODE EXAMPLE ########################################################################### filename: 'common.h' -------------------------------------------------------------------------- typedef struct { double height; double weight; int age; } __CONSTANTS; __constant__ __CONSTANTS d_const; --------------------------------------------------------------------------- filename: main.cu --------------------------------------------------------------------------- #include "common.h" #include "gpukernels.h" int main(int argc, char **argv) { __CONSTANTS T; T.height = 1.79; T.weight = 73.2; T.age = 26; cudaMemcpyToSymbol(d_consts, &T, sizeof(__CONSTANTS)); test_kernel <<< 1, 16 >>>(); cudaDeviceSynchronize(); } --------------------------------------------------------------------------- filename: gpukernels.h --------------------------------------------------------------------------- __global__ void test_kernel(); --------------------------------------------------------------------------- filename: gpukernels.cu --------------------------------------------------------------------------- #include <stdio.h> #include "gpukernels.h" #include "common.h" __global__ void test_kernel() { printf("Id: %d, height: %f, weight: %f\n", threadIdx.x, d_const.height, d_const.weight); } When I execute this code, the kernel executes, displays the thread ids, but the constant values are displayed as zeros. How can I fix this?

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  • GridView edit problem If primary key is editable (design problem)

    - by Nassign
    I would like to ask about the design of table based on it's editability in a Grid View. Let me explain. For example, I have a table named ProductCustomerRel. Method 1 CustomerCode varchar PK ProductCode varchar PK StoreCode varchar PK Quantity int Note text So the combination of the CustomerCode, StoreCode and ProductCode must be unique. The record is displayed on a gridview. The requirement is that you can edit the customer, product and storecode but when the data is saved, the PK constraint must still persist. The problem here is it would be natural for a grid to be able to edit the 3 primary key, you can only achieve the update operation of the grid view by first deleting the row and then inserting the row with the updated data. An alternative to this is to just update the table and add a SeqNo, and just enforce the unique constraint of the 3 columns when inserting and updating in the grid view. Method 2 SeqNo int PK CustomerCode varchar ProductCode varchar StoreCode varchar Quantity int Note text My question is which of the two method is better? or is there another way to do this?

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  • How to have synchronous writing to a file (Threads) ?

    - by bobby
    Hi all. I created and started some Threads that each one writes something to a common text file. but the following error appears to me: "The process cannot access the file 'C:\hello.txt' because it is being used by another process." void AccessFile() { int num = 5; Thread[] trds = new Thread[5]; for (int i = 0; i < num; i++) { trds[i] = new Thread(new ParameterizedThreadStart(WriteToFile)); } for (int i = 0; i < num; i++) { trds[i].Start(String.Format("{0}: Hello from thread id:#{1}", i, trds[i].ManagedThreadId)); } } void WriteToFile(object message) { string FileName = "C:\\hello.txt"; string mess = (string)message; System.IO.StreamWriter sw = null; FileStream objStream = null; sw = File.AppendText(FileName); if (sw == null) { objStream = new FileStream(FileName, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.ReadWrite); sw = new StreamWriter(objStream); } sw.WriteLine(mess); sw.Close(); sw.Dispose(); } the AccessFile() method is the starting point. could any one tell me what should i do?

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  • Using abstract base to implement private parts of a template class?

    - by StackedCrooked
    When using templates to implement mix-ins (as an alternative to multiple inheritance) there is the problem that all code must be in the header file. I'm thinking of using an abstract base class to get around that problem. Here's a code sample: class Widget { public: virtual ~Widget() {} }; // Abstract base class allows to put code in .cpp file. class AbstractDrawable { public: virtual ~AbstractDrawable() = 0; virtual void draw(); virtual int getMinimumSize() const; }; // Drawable mix-in template<class T> class Drawable : public T, public AbstractDrawable { public: virtual ~Drawable() {} virtual void draw() { AbstractDrawable::draw(); } virtual int getMinimumSize() const { return AbstractDrawable::getMinimumSize(); } }; class Image : public Drawable< Widget > { }; int main() { Image i; i.draw(); return 0; } Has anyone walked that road before? Are there any pitfalls that I should be aware of?

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  • MSSQL Server using multiple ID Numbers

    - by vincer
    I have an web application that creates printable forms, these forms have a unique number on them, the problem is I have 2 forms that separate numbers need to be created for them. ie) Form1- Numbered 2000000-2999999 Form2- Numbered 3000000-3999999 dbo.test2 - is my form information table Tsel - is my autoinc table for the 3000000 series numbers Tadv - is my autoinc table for the 2000000 series numbers What I have done is create 2 tables with just autoinc row (one for 2000000 series numbers and one for 3000000 series numbers), I then created a trigger to add a record to the coresponding table, read back the autoinc number and add it to my table that stores the form information including the just created autoinc number for the right series of forms. Although it does work, I'm concerned that the numbers will get messed up under load. I'm not sure the @@IDENTITY will always return the right value when many people are using the system. (I cannot have duplicates and I need to use the numbering form show above. Thanks for any help See code below. ** TRIGGER ** CREATE TRIGGER MAKEANID2 ON dbo.test2 AFTER INSERT AS SET NOCOUNT ON declare @someid int declare @someid2 int declare @startfrom int declare @test1 varchar(10) select @someid=@@IDENTITY select @test1 = (Select name1 from test2 where sysid = @someid ) if @test1 = 'select' begin insert into Tsel Default values select @someid2 = @@IDENTITY end if @test1 = 'adv' begin insert into Tadv Default values select @someid2 = @@IDENTITY end update test2 set name2=(@someid2) where sysid = @someid SET NOCOUNT OFF

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  • Beginner error in CUDA

    - by Dimitri
    Hi folks, first all i want to wish you a merry christmas. I am writing a small program in CUDA and i have the following errors : contraste.cu(167): error: calling a host function from a __device__/__global__ function is not allowed I don't understand why. Can you please help me and show me my errors. It seems that my program is correct. Here is a the bunch of code causing the problems : __global__ void kernel_contraste(float power, unsigned char tab_in[], unsigned char tab_out[], int nbl, int nbc) { int x = threadIdx.x; printf("I am the thread %d\n", x); } Part of my main program : unsigned char *dimg, *dimg_res; ..... cudaMalloc((void **)dimg, h * w * sizeof(char)); cudaMemcpy(dimg, r.data, h*w*sizeof(char), cudaMemcpyHostToDevice); cudaMalloc((void **)dimg_res, h*w*sizeof(char)); dim3 nbThreadparBloc(256); dim3 numblocs(1); kernel_contraste<<<numblocs, nbThreadparBloc >>>(puissance, dimg, dimg_res, h, w); cudaThreadSynchronize(); ..... cudaFree(dimg); cudaFree(dimg_res); The line 167 is the line where i call the printf in function kernel_contraste. For information, this program takes an image as an input( a sun Rasterfile ) and a power then it calculates the contraste of that image. Thanks !!

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  • How to customize file dialog in wpf

    - by ManjuAnoop
    In Windows7 I am using a customized Open File Dialog( WPF application). My Open File dialog is derived from Microsoft.Win32.CommonDialog. The dialog have old look, how to change this to new look (windows7 file dialog look(Explorer style)). Code portion: private const int OFN_ENABLESIZING = 0x00800000; private const int OFN_EXPLORER = 0x00080000; private const int OFN_ENABLEHOOK = 0x00000020; protected override bool RunDialog(IntPtr hwndOwner) { OPENFILENAME_I.WndProc proc = new OPENFILENAME_I.WndProc(this.HookProc); OPENFILENAME_I ofn = new OPENFILENAME_I(); this._charBuffer = CharBuffer.CreateBuffer(0x2000); if (this._fileNames != null) { this._charBuffer.PutString(this._fileNames[0]); } ofn.lStructSize = Marshal.SizeOf(typeof(OPENFILENAME_I)); ofn.hwndOwner = hwndOwner; ofn.hInstance = IntPtr.Zero; ofn.lpstrFilter = MakeFilterString(this._filter, this.DereferenceLinks); ofn.nFilterIndex = this._filterIndex; ofn.lpstrFile = this._charBuffer.AllocCoTaskMem(); ofn.nMaxFile = this._charBuffer.Length; ofn.lpstrInitialDir = this._initialDirectory; ofn.lpstrTitle = this._title; ofn.Flags = OFN_EXPLORER | OFN_ENABLESIZING | OFN_ENABLEHOOK; ofn.lpfnHook = proc; ofn.FlagsEx = 0x1000000 ; NativeMethods.GetOpenFileName(ofn); // } [SecurityCritical, SuppressUnmanagedCodeSecurity, DllImport("comdlg32.dll", CharSet = CharSet.Unicode, SetLastError = true)] internal static extern bool GetOpenFileName([In, Out] OPENFILENAME_I ofn);

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  • Why is joining two vectors simply not working?

    - by Jim
    I have two vectors of MyObj structs. MyObj is defined as follows: struct MyObj { float x, y; unsigned int data[8]; unsigned int tmp[1]; MyObj(const MyObj &m) { x = m.x; y = m.y; tmp[0] = 0; for (int i = 0; i < 8; ++i) { data[i] = m.data[i]; } } }; I then have two vectors... vector<MyObj> v1; vector<MyObj> v2; // both get data eventually. v1.insert(v1.end(), v2.begin(), v2.end()); v2 has 3535004 elements in my experiment. v1 is similarly sized. I've also tried building a new vector and just using .push_back to build it from both vectors. Essentially, when I try to merge the two vectors I just get an error from visual studio saying "Debug error! R6010, abort() has been called". Very non-useful... So my question is: what could be causing this error, and how can I solve it? Thank you

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  • How is an array stored in memory?

    - by George
    In an interest to delve deeper into how memory is allocated and stored, I have written an application that can scan memory address space, find a value, and write out a new value. I developed a sample application with the end goal to be able to programatically locate my array, and overwrite it with a new sequence of numbers. In this situation, I created a single dimensional array, with 5 elements, e.g. int[] array = new int[] {8,7,6,5,4}; I ran my application and searched for a sequence of the five numbers above. I was looking for any value that fell between 4 and 8, for a total of 5 numbers in a row. Unforuntately, my the sequential numbers in my array matched hundreds of results, as the numbers 4 through 8, in no particular sequence happened to be next to each other, in memory, in many situations. Is there any way to distinguish that a set of numbers within memory, represents an array, not simply integers that are next to each other? Is there any way of knowing that if I find a certain value, that the matching values proceeding it are that of an array? I would assume that when I declare int[] array, its pointing at the first address of my array, which would provide some kind of meta-data to what existed in the array, e.g. 0x123456789 meta-data, 5 - 32 bit integers 0x123456789 + 32 "8" 0x123456789 + 64 "7" 0x123456789 + 96 "6" 0x123456789 + 128 "5" 0x123456789 + 160 "4" Am I way off base?

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  • OpenCV compare two images and get different pixels

    - by Richard Knop
    For some reason the code bellow is not working. I have two 640*480 images which are very similar but not the same (at least few hundred/thousand pixels should be different). This is how I am comparing them and counting different pixels: unsigned char* row; unsigned char* row2; int count = 0; // this happens in a loop // fIplImageHeader is current image // lastFIplImageHeader is image from previous iteration if ( NULL != lastFIplImageHeader->imageData ) { for( int y = 0; y < fIplImageHeader->height; y++ ) { row = &CV_IMAGE_ELEM( fIplImageHeader, unsigned char, y, 0 ); row2 = &CV_IMAGE_ELEM( lastFIplImageHeader, unsigned char, y, 0 ); for( int x = 0; x < fIplImageHeader->width*fIplImageHeader->nChannels; x += fIplImageHeader->nChannels ) { if (row[x] == row2[x]) // the pixel in the first channel (usually G) { count++; } if (row[x+1] == row2[x+1]) // ... second channel (usually B) { count++; } if (row[x+2] == row2[x+2]) // ... third channel (usually R) { count++; } } } } Now at the end I get number 3626 which would seem alright. But, I tried opening one of the images in MS Paint and drawing thick red lines all over it which should increase the number of different pixels substantially. I got the same number again: 3626. Obviously I am doing something wrong here. I am comparing these images in a loop. This line is before the loop: IplImage* lastFIplImageHeader = cvCreateImageHeader(cvSize(640, 480), 8, 3); Then inside the loop I load images like this: IplImage* fIplImageHeader = cvLoadImage( filePath.c_str() ); // here I compare the pixels (the first code snippet) lastFIplImageHeader->imageData = fIplImageHeader->imageData; So lastFIplImageHeader is storing the image from the previous iteration and fIplImageHeader is storing the current image.

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  • How do I specify the foreign key on a many-to-one relationship when is not a property on the object

    - by jjujuma
    I'm trying to map a many-to-one relationship from MarketMenuBranch to Market. My classes look like: public class Market implements Serializable { private int id; private String name; private List<MarketMenuBranch> marketMenuBranches; // accessors / mutators etc... public class MarketMenuBranch implements Serializable { private MarketMenuBranchId id; private String name; // accessors / mutators etc... public class MarketMenuBranchId implements Serializable { private int marketId; private int sequence; // accessors / mutators etc... But I don't know what I can put for the property name (where I have ???? below). I really want to put id.marketId but that seems to be wrong. <class name="MarketMenuBranch" table="MARKET_MENU_BRANCH"> <composite-id name="id" class="MarketMenuBranchId"> <key-property name="marketId"/> <key-property name="sequence"/> </composite-id> <property name="name"/> <many-to-one name="????????"/> </class> How can I do this?

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  • Want to convert whole PHP script in RUBY ON RAILS

    - by user303058
    // set image quality (from 0 to 100, not applicable to gif) $imgquality = 100; // get data from $_POST or $_GET ? $data = &$_POST; // get image dimensions $width = (int) $data['width']; $height = (int) $data['height']; // create image object $img = imagecreatetruecolor($width, $height); // populate image with pixels for ($y = 0; $y < $height; $y++) { // innitialize $x = 0; // get row data $row = explode(',', $data['r'.$y]); // place row pixels $cnt = sizeof($row); for ($r = 0; $r < $cnt; $r++) { // get pixel(s) data $pixel = explode(':', $row[$r]); // get color $pixel[0] = str_pad($pixel[0], 6, '0', STR_PAD_LEFT); $cr = hexdec(substr($pixel[0], 0, 2)); $cg = hexdec(substr($pixel[0], 2, 2)); $cb = hexdec(substr($pixel[0], 4, 2)); // allocate color $color = imagecolorallocate($img, $cr, $cg, $cb); // place repeating pixels $repeat = isset($pixel[1]) ? (int) $pixel[1] : 1; for ($c = 0; $c < $repeat; $c++) { // place pixel imagesetpixel($img, $x, $y, $color); // iterate column $x++; } } } // set proper content type header('Content-type: image/'.$imgtype); header('Content-Disposition: attachment; filename="chart.'.$imgtype.'"'); // stream image $function = 'image'.$imgtype; if ($imgtype == 'gif') { $function($img); } else { $function($img, null, $imgquality); } // destroy imagedestroy($img); ?

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  • why no implicit conversion from pointer to reference to const pointer.

    - by user316606
    I'll illustrate my question with code: #include <iostream> void PrintInt(const unsigned char*& ptr) { int data = 0; ::memcpy(&data, ptr, sizeof(data)); // advance the pointer reference. ptr += sizeof(data); std::cout << std::hex << data << " " << std::endl; } int main(int, char**) { unsigned char buffer[] = { 0x11, 0x11, 0x11, 0x11, 0x22, 0x22, 0x22, 0x22, }; /* const */ unsigned char* ptr = buffer; PrintInt(ptr); // error C2664: ... PrintInt(ptr); // error C2664: ... return 0; } When I run this code (in VS2008) I get this: error C2664: 'PrintInt' : cannot convert parameter 1 from 'unsigned char *' to 'const unsigned char *&'. If I uncomment the "const" comment it works fine. However shouldn't pointer implicitly convert into const pointer and then reference be taken? Am I wrong in expecting this to work? Thanks!

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  • JSON can't read, key reading fail maybe

    - by Abdullah Al Mubarok
    I wonder why I can't read the JSON Object like this : { "1":{"bulan":"Januari","tahun":"2012","tagihan":"205000","status":"Lunas"}, "2":{"bulan":"Februari","tahun":"2012","tagihan":"180000","status":"Lunas"}, "3":{"bulan":"Maret","tahun":"2012","tagihan":"120000","status":"Lunas"}, "4":{"bulan":"April","tahun":"2012","tagihan":"230000","status":"Lunas"}, "5":{"bulan":"Mei","tahun":"2012","tagihan":"160000","status":"Lunas"}, "6":{"bulan":"Juni","tahun":"2012","tagihan":"150000","status":"Belum Lunas"}, "panjang":6 } with my android code like this : try { int length = jobj.getInt("panjang"); for(int n = 0; n < length; n++){ String m = Integer.toString(n) JSONObject row = jobj.getJSONObject(m); String bulan = row.getString("bulan"); String tahun = row.getString("tahun"); String tagihan = row.getString("tagihan"); String status = row.getString("status"); HashMap<String, String> map = new HashMap<String, String>(); map.put("bulan", bulan); map.put("tahun", tahun); map.put("tagihan", tagihan); map.put("status", status); list.add(map); } } catch (JSONException e) { e.printStackTrace(); } It always return nothing, but it works fine if I change the key m to specific key like if String m = "1"; and I can't use JSONObject row = jobj.getJSONObject(n); because getJSONObject() just accept string, not int. is there something wrong with my code?

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  • Foreach loop and tasks.

    - by Scott Chamberlain
    I know from the codeing guidlines that I have read you should not do for (int i = 0; i < 5; i++) { Task.Factory.StartNew(() => Console.WriteLine(i)); } Console.ReadLine(); as it will write 5 5's, I understand that and I think i understand why it is happening. I know the solution is just to do for (int i = 0; i < 5; i++) { int localI = i; Task.Factory.StartNew(() => Console.WriteLine(localI)); } Console.ReadLine(); However is something like this ok to do? foreach (MyClass myClass in myClassList) { Task.Factory.StartNew(() => myClass.DoAction()); } Console.ReadLine(); Or do I need to do the same thing I did in the for loop. foreach (MyClass myClass in myClassList) { MyClass localMyClass = myClass; Task.Factory.StartNew(() => localMyClass.DoAction()); } Console.ReadLine();

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  • Generating new tasks in a foreach loop

    - by Scott Chamberlain
    I know from the codeing guidlines that I have read you should not do for (int i = 0; i < 5; i++) { Task.Factory.StartNew(() => Console.WriteLine(i)); } Console.ReadLine(); as it will write 5 5's, I understand that and I think i understand why it is happening. I know the solution is just to do for (int i = 0; i < 5; i++) { int localI = i; Task.Factory.StartNew(() => Console.WriteLine(localI)); } Console.ReadLine(); However is something like this ok to do? Task currentTask = myFirstTask; currentTask.Start(); foreach (Task task in _TaskList) { currentTask.ContinueWith((antecendent) => { if(antecendent.IsCompleated) { task.Start(); } else //do error handling; }); currentTask = task; } } or do i need to do this? Task currentTask = myFirstTask; foreach (Task task in _TaskList) { Task localTask = task; currentTask.ContinueWith((antecendent) => { if(antecendent.IsCompleated) { localTask.Start(); } else //do error handling; }); currentTask = task; }

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  • Overhead of calling tiny functions from a tight inner loop? [C++]

    - by John
    Say you see a loop like this one: for(int i=0; i<thing.getParent().getObjectModel().getElements(SOME_TYPE).count(); ++i) { thing.getData().insert( thing.GetData().Count(), thing.getParent().getObjectModel().getElements(SOME_TYPE)[i].getName() ); } if this was Java I'd probably not think twice. But in performance-critical sections of C++, it makes me want to tinker with it... however I don't know if the compiler is smart enough to make it futile. This is a made up example but all it's doing is inserting strings into a container. Please don't assume any of these are STL types, think in general terms about the following: Is having a messy condition in the for loop going to get evaluated each time, or only once? If those get methods are simply returning references to member variables on the objects, will they be inlined away? Would you expect custom [] operators to get optimized at all? In other words is it worth the time (in performance only, not readability) to convert it to something like: ElementContainer &source = thing.getParent().getObjectModel().getElements(SOME_TYPE); int num = source.count(); Store &destination = thing.getData(); for(int i=0;i<num;++i) { destination.insert(thing.GetData().Count(), source[i].getName(); } Remember, this is a tight loop, called millions of times a second. What I wonder is if all this will shave a couple of cycles per loop or something more substantial? Yes I know the quote about "premature optimisation". And I know that profiling is important. But this is a more general question about modern compilers, Visual Studio in particular.

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  • parsing ssid with iwconfig in c

    - by user1781595
    I am about building a bar for DWM (ubuntu linux), showing wifi details such as the ssid. Thats my code: #include <stdio.h> #include <stdlib.h> int main( int argc, char *argv[] ) { FILE *fp; int status; char path[1035]; /* Open the command for reading. */ fp = popen("iwconfig", "r"); if (fp == NULL) { printf("Failed to run command\n" ); exit; } char s[500]; /* Read the output a line at a time - output it. */ while (fgets(path, sizeof(path)-1, fp) != NULL) { sprintf(s,"%s%s",s, path); } //printf("%s",s); /* close */ pclose(fp); char delimiter[1] = "s"; char *ptr; ptr = strtok(s, delimiter); printf("SSID: %s\n", ptr); return 0; } i am getting overflowerrors and dont know what to do. I dont think, thats a good way to get the ssid either... :/ Suggestions?

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  • explain notifier.c from the Linux kernel

    - by apollon
    I'm seeking to fully understand the following code snippet from kernel/notifier.c. I have read and built simple link lists and think I get the construct from K&R's C programming. The second line below which begins with the 'int' appears to be two items together which is unclear. The first is the (*notifier_call) which I believe has independent but related significance with the second containing a 'notifier block' term. Can you explain how it works in detail? I understand that there is a function pointer and multiple subscribers possible. But I lack the way to tie these facts together, and could use a primer or key so I exactly understand how the code works. The third line looks to contain the linking structure, or recursive nature. Forgive my terms, and correct them as fit as I am a new student of computer science terminology. struct notifier_block { int (*notifier_call)(struct notifier_block *, unsigned long, void *); struct notifier_block *next; int priority; };

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  • Passing Data to Multi Threads

    - by alaamh
    I study this code from some book: #include <pthread.h> #include <stdio.h> /* Parameters to print_function. */ struct char_print_parms { /* The character to print. */ char character; /* The number of times to print it. */ int count; }; /* Prints a number of characters to stderr, as given by PARAMETERS, which is a pointer to a struct char_print_parms. */ void* char_print(void* parameters) { /* Cast the cookie pointer to the right type. */ struct char_print_parms* p = (struct char_print_parms*) parameters; int i; for (i = 0; i < p->count; ++i) fputc(p->character, stderr); return NULL; } /* The main program. */ int main() { pthread_t thread1_id; pthread_t thread2_id; struct char_print_parms thread1_args; struct char_print_parms thread2_args; /* Create a new thread to print 30,000 ’x’s. */ thread1_args.character = 'x'; thread1_args.count = 30000; pthread_create(&thread1_id, NULL, &char_print, &thread1_args); /* Create a new thread to print 20,000 o’s. */ thread2_args.character = 'o'; thread2_args.count = 20000; pthread_create(&thread2_id, NULL, &char_print, &thread2_args); usleep(20); return 0; } after running this code, I see different result each time. and some time corrupted result. what is wrong and what the correct way to do that?

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  • Pointers into elements in a container

    - by Pillsy
    Say I have an object: struct Foo { int bar_; Foo(int bar) bar_(bar) {} }; and I have an STL container that contains Foos, perhaps a vector, and I take // Elsewhere... vector<Foo> vec; vec.push_back(Foo(4)); int *p = &(vec[0].bar_) This is a terrible idea, right? The reason is that vector is going to be storing its elements in a dynamically allocated array somewhere, and eventually, if you add enough elements, it will have to allocate another array, copy over all the elements of the original array, and delete the old array. After that happens, p points to garbage. This is why many operations on a vector will invalidate iterators. It seems like it would be reasonable to assume that an operation that would invalidate iterators from a container will also invalidate pointers to data members of container elements, and that if an operation doesn't invalidate iterators, those pointers will still be safe. However, many reasonable assumptions are false. Is this one of them?

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