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• Figuring out the performance limitation of an ADC on a PIC microcontroller

  - by AKE

  I'm spec-ing the suitability of a microcontroller like PIC for an analog-to-digital application. This would be preferable to using external A/D chips. To do that, I've had to run through some computations, pulling the relevant parameters from the datasheets. I'm not sure I've got it right -- would appreciate a check! Here's the simplest example: PIC10F220 is the simplest possible PIC with an ADC. Runs at clock speed of 8MHz. Has an instruction cycle of 0.5us (4 clock steps per instruction) So: Taking Tacq = 6.06 us (acquisition time for ADC, assume chip temp. = 50*C) [datasheet p34] Taking Fosc = 8MHz (? clock speed) Taking divisor = 4 (4 clock steps per CPU instruction) This gives TAD = 0.5us (TAD = 1/(Fosc/divisor) ) Conversion time is 13*TAD [datasheet p31] This gives conversion time 6.5us ADC duration is then 12.56 us [? Tacq + 13*TAD] Assuming at least 2 instructions for load/store: This is another 1 us [0.5 us per instruction] Which would give max sampling rate of 73.7 ksps (1/13.56) Supposing 8 more instructions for real-time processing: This is another 4 us Thus, total ADC/handling time = 17.56us (12.56us + 1us + 4us) So expected upper sampling rate is 56.9 ksps. Nyquist frequency for this sampling rate is therefore 28 kHz. If this is right, it suggests the (theoretical) performance suitability of this chip's A/D is for signals that are bandlimited to 28 kHz. Is this a correct interpretation of the information given in the data sheet? Any pointers would be much appreciated! AKE

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• Simulating pass by reference for an array in Java

  - by Leif Andersen

  I was wondering, in java, is it possible to in anyway, simulate pass by reference for an array? Yes, I know the language doesn't support it, but is there anyway I can do it. Say, for example, I want to create a method that reverses the order of all the elements in an array. (I know that this code snippet isn't the best example, as there is a better algorithms to do this, but this is a good example of the type of thing I want to do for more complex problems). Currently, I need to make a class like this: public static void reverse(Object[] arr) { Object[] tmpArr = new Object[arr.length]; count = arr.length - 1; for(Object i : arr) tmpArr[count--] = i; // I would like to do arr = tmpArr, but that will only make the shallow // reference tmpArr, I would like to actually change the pointer they passed in // Not just the values in the array, so I have to do this: count = arr.length - 1; for(Object i : tmpArr) arr[count--] = i; return; } Yes, I know that I could just swap the values until I get to the middle, and it would be much more efficient, but for other, more complex purposes, is there anyway that I can manipulate the actual pointer? Again, thank you.

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• Where my memory is alloced, Stack or Heap, Can I find it at Run-time?

  - by AKN

  I know that memory alloced using new, gets its space in heap, and so we need to delete it before program ends, to avoid memory leak. Let's look at this program... Case 1: char *MyData = new char[20]; _tcscpy(MyData,"Value"); . . . delete[] MyData; MyData = NULL; Case 2: char *MyData = new char[20]; MyData = "Value"; . . . delete[] MyData; MyData = NULL; In case 2, instead of allocating value to the heap memory, it is pointing to a string literal. Now when we do a delete it would crash, AS EXPECTED, since it is not trying to delete a heap memory. Is there a way to know where the pointer is pointing to heap or stack? By this the programmer Will not try to delete any stack memory He can investigate why does this ponter, that was pointing to a heap memory initially, is made to refer local literals? What happened to the heap memory in the middle? Is it being made to point by another pointer and delete elsewhere and all that?

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• Simulating pass by reference for an array reference (i.e. a reference to a reference) in Java

  - by Leif Andersen

  I was wondering, in java, is it possible to in anyway, simulate pass by reference for an array? Yes, I know the language doesn't support it, but is there anyway I can do it. Say, for example, I want to create a method that reverses the order of all the elements in an array. (I know that this code snippet isn't the best example, as there is a better algorithms to do this, but this is a good example of the type of thing I want to do for more complex problems). Currently, I need to make a class like this: public static void reverse(Object[] arr) { Object[] tmpArr = new Object[arr.length]; count = arr.length - 1; for(Object i : arr) tmpArr[count--] = i; // I would like to do arr = tmpArr, but that will only make the shallow // reference tmpArr, I would like to actually change the pointer they passed in // Not just the values in the array, so I have to do this: count = arr.length - 1; for(Object i : tmpArr) arr[count--] = i; return; } Yes, I know that I could just swap the values until I get to the middle, and it would be much more efficient, but for other, more complex purposes, is there anyway that I can manipulate the actual pointer? Again, thank you.

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• Position an icon on the right in the middle of a list item

  - by Andy

  I have the following code which prints an img if the current page is selected. The issue i have is if the list item is a varied height i cant position it in the middle of the list item on the far right... <li><?php echo $child->link($child->title); ?><?php echo (url_start_with($child->url) ? '<img src="images/ico-arrow.png" class="pointer">': null); ?></li> how can i ammend the "TOP" so that it will position itself vertically no matter what the height using css #bf-fest-list li { margin:0; padding:5px 25px; position:relative; } #bf-fest-list li a:hover { color:#ec1c23; text-decoration:none; } #bf-fest-list li.current { background:#a0a1a4; padding:10px 25px; } #bf-fest-list li.current a { color:#FFF; } #bf-fest-list li .pointer { position:absolute; top:10px; left:233px; }

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• Cooperative/Non-preemptive threading avoiding threadlooks?

  - by Wayne

  Any creative ideas to avoid deadlocks on a yield or sleep with cooperative/non-preemptive multitasking without doing an O/S Thread.Sleep(10)? Typically the yield or sleep call will call back into the scheduler to run other tasks. But this can sometime produce deadlocks. Some background: This application has enormous need for speed and, so far, it's extremely fast as compared to other systems in the same industry. One of the speed techniques is cooperative/non-preemptive threading rather then the cost of a context switch from O/S threads. The high level design a priority manager which calls out to tasks depending on priority and processing time. Each task does one "iteration" of work and returns to wait its turn again in the priority queue. The tricky thing with non-preemptive threading is what to do when you want to a particular task to stop in the middle of work and wait for some other event from a different task before continuing. In this case, we have 3 tasks, A B and C where A is a controller that must synchronize the activity of B and C. First, A starts both B and C. Then B yields so C gets invoked. When C yields, A sees they are both inactive, decides it's time for B to run but not time for C yet. Well B is now stuck in a yield that has called C, so it can never run. Sincerely, Wayne

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• Figuring out the Nyquist performance limitation of an ADC on an example PIC microcontroller

  - by AKE

  I'm spec-ing the suitability of a dsPIC microcontroller for an analog-to-digital application. This would be preferable to using dedicated A/D chips and a separate dedicated DSP chip. To do that, I've had to run through some computations, pulling the relevant parameters from the datasheets. I'm not sure I've got it right -- would appreciate a check! (EDITED NOTE: The PIC10F220 in the example below was selected ONLY to walk through a simple example to check that I'm interpreting Tacq, Fosc, TAD, and divisor correctly in working through this sort of Nyquist analysis. The actual chips I'm considering for the design are the dsPIC33FJ128MC804 (with 16b A/D) or dsPIC30F3014 (with 12b A/D).) A simple example: PIC10F220 is the simplest possible PIC with an ADC Runs at clock speed of 8MHz. Has an instruction cycle of 0.5us (4 clock steps per instruction) So: Taking Tacq = 6.06 us (acquisition time for ADC, assume chip temp. = 50*C) [datasheet p34] Taking Fosc = 8MHz (? clock speed) Taking divisor = 4 (4 clock steps per CPU instruction) This gives TAD = 0.5us (TAD = 1/(Fosc/divisor) ) Conversion time is 13*TAD [datasheet p31] This gives conversion time 6.5us ADC duration is then 12.56 us [? Tacq + 13*TAD] Assuming at least 2 instructions for load/store: This is another 1 us [0.5 us per instruction] Which would give max sampling rate of 73.7 ksps (1/13.56) Supposing 8 more instructions for real-time processing: This is another 4 us Thus, total ADC/handling time = 17.56us (12.56us + 1us + 4us) So expected upper sampling rate is 56.9 ksps. Nyquist frequency for this sampling rate is therefore 28 kHz. If this is right, it suggests the (theoretical) performance suitability of this chip's A/D is for signals that are bandlimited to 28 kHz. Is this a correct interpretation of the information given in the data sheet in obtaining the Nyquist performance limit? Any opinions on the noise susceptibility of ADCs in PIC / dsPIC chips would be much appreciated! AKE

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• Opacity CSS not working in IE8

  - by Alistair Christie

  I'm using CSS to indicate the trigger text for a jQuery slide-down section: i.e. when you hover over the trigger text the cursor changes to a pointer and the opacity of the trigger text is reduced to indicate that the text has a click action. This works fine in Firefox and Chrome, but in IE8 the opacity doesn't change. I've tried a variety of CSS settings without any success. For example HTML: <h3 class="slidedownTrigger">This is the trigger text</h3> CSS: .slidedownTrigger {     cursor: pointer;     -ms-filter: “progid:DXImageTransform.Microsoft.Alpha(Opacity=75)”;     filter: alpha(opacity=75);     -khtml-opacity: 0.75;     -moz-opacity: 0.75;     opacity: 0.75; } What's stopping IE changing the opacity? Note: I've tried this on a variety of different elements, swapping round the order of the CSS statements, and just using the IE ones on their own. I've also tried using -ms-filter: "alpha(opacity=75)"; but with no success. I've run out of things to try to get opacity modification working in IE8. Any ideas?

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• Getting hardware floating point with android NDK

  - by Goz

  Hi All, I've begun playing with the android NDK. One of the things I've just learnt is about creating an application.mk file to specify the armv7 abi. I'm building the san-angeles example with the following parameters. APP_MODULES := sanangeles APP_PROJECT_PATH := $(call my-dir)/../ APP_OPTIM := release APP_ABI := armeabi-v7a However this seems to run at exactly the same speed as it did before (ie badly). Am I just GL limited and not CPU limited or is something wrong here? I have noticed when I compile that I get the following command line options emitted: -march=armv7-a -mfloat-abi=softfp -mfpu=vfp -mthumb The thing that worries me there is the "softfp". There IS mention of the v7 abi, the VFP fpu stuff and I'm guessing the "thumb" refers to the "thumb-2" instructions (Though I don't know what exactly these are). However that "softfp" does concern me. Shouldn't it be "hardfp"? Anyone got any ideas on these questions? I think I'm probably about ready to start implementing some GL ES 2.0 code for my HTC Desire but I'd like to make sure I'm getting the best possible speed out of it :) Cheers in advance!

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• Declaration of arrays before "normal" variables in c?

  - by bjarkef

  Hi We are currently developing an application for a msp430 MCU, and are running into some weird problems. We discovered that declaring arrays withing a scope after declaration of "normal" variables, sometimes causes what seems to be undefined behavior. Like this: foo(int a, int *b); int main(void) { int x = 2; int arr[5]; foo(x, arr); return 0; } foo sometimes is passed a pointer as the second variable, that does not point to the arr array. We verify this by single stepping through the program, and see that the value of the arr variable in the main scope is not the same as the value of the b pointer variable in the foo scope. And no, this is not really reproduceable, we have just observed this behavior once in a while. Changing the example seems to solve the problem, like this: foo(int a, int *b); int main(void) { int arr[5]; int x = 2; foo(x, arr); return 0; } Does anybody have any input or hints as to why we experience this behavior? Or similar experiences? The MSP430 programming guide specifies that code should conform to the ANSI C89 spec. and so I was wondering if it says that arrays has to be declared before non-array variables? Any input on this would be appreciated.

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• Printing an invisible NSView

  - by Rodger Wilson

  Initially I created a simple program with a custom NSView. I drew a picture (certificate) and printed it! beautiful! Everything worked great! I them moved my custom NSView to an existing application. My hope was that when a user hit print it would print this certificate. Simple enough. I figured a could have a NSView pointer in my controller code. Then at initialization I would populate the pointer. Then when someone wanted to print the certificate it would print. The problem is that all of my drawing code is in the "drawRect" method. This method doesn't get called because this view is never displayed in a window. I have heart that others use non-visible NSView objects just for printing. What do I need to do. I really don't want to show this view to the screen. Rodger

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• Finding a 3rd party QWidget with injected code & QWidget::find(hwnd)

  - by David Menard

  Hey, I have a Qt Dll wich I inject into a third-party Application using windows detours library: if(!DetourCreateProcessWithDll( Path, NULL, NULL, NULL, TRUE, CREATE_DEFAULT_ERROR_MODE | CREATE_SUSPENDED, NULL, NULL, &si, &pi, "C:\\Program Files\\Microsoft Research\\Detours Express 2.1\\bin\\detoured.dll", "C:\\Users\\Dave\\Documents\\Visual Studio 2008\\Projects\\XOR\\Debug\\XOR.dll", NULL)) and then I set a system-wide hook to intercept window creation: HHOOK h_hook = ::SetWindowsHookEx(WH_CBT, (HOOKPROC)CBTProc, Status::getInstance()->getXORInstance(), 0); Where XOR is my programs name, and Status::getInstance() is a Singleton where I keep globals. In my CBTProc callback, I want to intercept all windows that are QWidgets: HWND hwnd= FindWindow(L"QWidget", NULL); which works well, since I get a corresponding HWND (I checked with Spy++) Then, I want to get a pointer to the QWidget, so I can use its functions: QWidget* q = QWidget::find(hwnd); but here's the problem, the returned pointer is always 0. Am I not injecting my code into the process properly? Or am I not using QWidget::find() as I should? Thanks, Dave EDIT:If i change the QWidget::find() function to an exported function of my DLL, after setting the hooks (so I can set and catch a breakpoint), QWidgetPrivate::mapper is NULL.

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• Save QList<int> to QSettings

  - by Tobias

  Hello, I want to save a QList<int> to my QSettings without looping through it. I know that I could use writeArray() and a loop to save all items or to write the QList to a QByteArray and save this but then it is not human readable in my INI file.. Currently I am using the following to transform my QList<int> to QList<QVariant>: QList<QVariant> variantList; //Temp is the QList<int> for (int i = 0; i < temp.size(); i++) variantList.append(temp.at(i)); And to save this QList<Variant> to my Settings I use the following code: QVariant list; list.setValue(variantList); //saveSession is my QSettings object saveSession.setValue("MyList", list); The QList is correctly saved to my INI file as I can see (comma seperated list of my ints) But the function crashes on exit. I already tried to use a pointer to my QSettings object instead but then it crashes on deleting the pointer ..

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• C function const multidimensional-array argument strange warning

  - by rogi

  Ehllo, I'm getting some strange warning about this code: typedef double mat4[4][4]; void mprod4(mat4 r, const mat4 a, const mat4 b) { /* yes, function is empty */ } int main() { mat4 mr, ma, mb; mprod4(mr, ma, mb); } gcc output as follows: $ gcc -o test test.c test.c: In function 'main': test.c:13: warning: passing argument 2 of 'mprod4' from incompatible pointer type test.c:4: note: expected 'const double (*)[4]' but argument is of type 'double (*)[4]' test.c:13: warning: passing argument 3 of 'mprod4' from incompatible pointer type test.c:4: note: expected 'const double ()[4]' but argument is of type 'double ()[4]' defining the function as: void mprod4(mat4 r, mat4 a, mat4 b) { } OR defining matrices at main as: mat4 mr; const mat4 ma; const mat4 mb; OR calling teh function in main as: mprod4(mr, (const double(*)[4])ma, (const double(*)[4])mb); OR even defining mat4 as: typedef double mat4[16]; make teh warning go away. Wat is happening here? Am I doing something invalid? gcc version is 4.4.3 if relevant. Thanks for your attention.

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• A queue in C using structs and dynamic memory allocation (linked list)

  - by Martin Pugh

  I am tasked with making a queue data structure in C, as a linked list. Our lecturer gave us a large amount of code to implement a stack, but we have to adapt it to create a queue. The code our lecturer gave us ends up not compiling and segfaulting at the exact same point as the code I wrote for the queue. I'm very new to structs, malloc and C in general, so there could be something painfully obvious I've overlooked. Here is the code I am using: #include <stdio.h> #include <stdlib.h> struct node{ int data; //contains the actual data struct node *prev; //pointer to previous node (Closer to front) struct node *next; //pointer to next node (Closer to back) }; typedef struct node *Nodepointer; struct queue{ Nodepointer front; Nodepointer back; }; typedef struct queue *Queuepointer; main(){ Queuepointer myqueue; //create a queue called myqueue init(myqueue); //initialise the queue Nodepointer new = (Nodepointer)malloc(sizeof(struct node)); myqueue->front = new; } int init(Queuepointer q){ q = (Queuepointer)malloc(sizeof(struct queue)); q->front = NULL; q->back = NULL; } The idea is that the queue struct 'contains' the first and last nodes in a queue, and when a node is created, myqueue is updated. However, I cannot even get to that part (pop and push are written but omitted for brevity). The code is segfaulting at the line myqueue->front = new; with the following gdb output: Program received signal SIGSEGV, Segmentation fault. 0x08048401 in main () at queue.c:27 27 myqueue->front = new; Any idea what I'm doing wrong?

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• sIFR - getting a:hover to work in navigation list

  - by HudRom

  Hi, I am currently struggling with sIFR and a:hover. My problem site is hosted at http://irene.huditsch.info I have the following HTML code: <body id="irene-huditsch-info"> <div id="header"> <h1>Irene Huditsch</h1> <div id="top-nav"> <ul> <li id="impressum"> <a href="impressum.html" rel="index">Impressum</a> </li> <li id="kontakt"> <a href="kontakt.html">Kontakt</a> </li> </ul> </div> ... My sIFR-config.js looks like: sIFR.replace(braganza, { selector: 'div#top-nav a', css: '.sIFR-root { background-color: transparent; color: #FFFFFF; line-height: 13px; font-size: 11px; text-decoration: underline; cursor: pointer; } .sIFR-root:hover { color: #592b02; }', wmode: 'transparent' }); But the hover doesn't take effect. I tried different solution with no success either. When I write sIFR.replace(braganza, { selector: 'div#top-nav li', css: 'a { background-color: transparent; color: #FFFFFF; line-height: 13px; font-size: 11px; text-decoration: underline; cursor: pointer; } a:hover { color: #592b02; }', wmode: 'transparent' }); (which seems logical to me), the list items are not rendered at all. Could you please give me an advice how to do it correctly with the structure given? Thanks, Roman

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• What's the fastest way to bulk insert a lot of data in SQL Server (C# client)

  - by Andrew

  I am hitting some performance bottlenecks with my C# client inserting bulk data into a SQL Server 2005 database and I'm looking for ways in which to speed up the process. I am already using the SqlClient.SqlBulkCopy (which is based on TDS) to speed up the data transfer across the wire which helped a lot, but I'm still looking for more. I have a simple table that looks like this: CREATE TABLE [BulkData]( [ContainerId] [int] NOT NULL, [BinId] [smallint] NOT NULL, [Sequence] [smallint] NOT NULL, [ItemId] [int] NOT NULL, [Left] [smallint] NOT NULL, [Top] [smallint] NOT NULL, [Right] [smallint] NOT NULL, [Bottom] [smallint] NOT NULL, CONSTRAINT [PKBulkData] PRIMARY KEY CLUSTERED ( [ContainerIdId] ASC, [BinId] ASC, [Sequence] ASC )) I'm inserting data in chunks that average about 300 rows where ContainerId and BinId are constant in each chunk and the Sequence value is 0-n and the values are pre-sorted based on the primary key. The %Disk time performance counter spends a lot of time at 100% so it is clear that disk IO is the main issue but the speeds I'm getting are several orders of magnitude below a raw file copy. Does it help any if I: Drop the Primary key while I am doing the inserting and recreate it later Do inserts into a temporary table with the same schema and periodically transfer them into the main table to keep the size of the table where insertions are happening small Anything else? -- Based on the responses I have gotten, let me clarify a little bit: Portman: I'm using a clustered index because when the data is all imported I will need to access data sequentially in that order. I don't particularly need the index to be there while importing the data. Is there any advantage to having a nonclustered PK index while doing the inserts as opposed to dropping the constraint entirely for import? Chopeen: The data is being generated remotely on many other machines (my SQL server can only handle about 10 currently, but I would love to be able to add more). It's not practical to run the entire process on the local machine because it would then have to process 50 times as much input data to generate the output. Jason: I am not doing any concurrent queries against the table during the import process, I will try dropping the primary key and see if that helps. ~ Andrew

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• array of structs in C

  - by Hristo

  I'm trying to create an array of structs and also a pointer to that array. I don't know how large the array is going to be, so it should be dynamic. My struct would look something like this: typedef struct _stats_t { int hours[24]; int numPostsInHour; int days[7]; int numPostsInDay; int weeks[20]; int numPostsInWeek; int totNumLinesInPosts; int numPostsAnalyzed; } stats_t; ... and I need to have multiple of these structs for each file (unknown amount) that I will analyze. I'm not sure how to do this. I don't like the following approach because of the limit of the size of the array: # define MAX 10 typedef struct _stats_t { int hours[24]; int numPostsInHour; int days[7]; int numPostsInDay; int weeks[20]; int numPostsInWeek; int totNumLinesInPosts; int numPostsAnalyzed; } stats_t[MAX]; So how would I create this array? Also, would a pointer to this array would look something this? stats_t stats[]; stats_t *statsPtr = &stats[0]; Thanks, Hristo

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• Microsoft Detours - DetourUpdateThread?

  - by pault543

  Hi, I have a few quick questions about the Microsoft Detours Library. I have used it before (successfully), but I just had a thought about this function: LONG DetourUpdateThread(HANDLE hThread); I read elsewhere that this function will actually suspend the thread until the transaction completes. This seems odd since most sample code calls: DetourUpdateThread(GetCurrentThread()); Anyway, apparently this function "enlists" threads so that, when the transaction commits (and the detours are made), their instruction pointers are modified if they lie "within the rewritten code in either the target function or the trampoline function." My questions are: When the transaction commits, is the current thread's instruction pointer going to be within the DetourTransactionCommit function? If so, why should we bother enlisting it to be updated? Also, if the enlisted threads are suspended, how can the current thread continue executing (given that most sample code calls DetourUpdateThread(GetCurrentThread());)? Finally, could you suspend all threads for the current process, avoiding race conditions (considering that threads could be getting created and destroyed at any time)? Perhaps this is done when the transaction begins? This would allow us to enumerate threads more safely (as it seems less likely that new threads could be created), although what about CreateRemoteThread()? Thanks, Paul For reference, here is an extract from the simple sample: // DllMain function attaches and detaches the TimedSleep detour to the // Sleep target function. The Sleep target function is referred to // through the TrueSleep target pointer. BOOL WINAPI DllMain(HINSTANCE hinst, DWORD dwReason, LPVOID reserved) { if (dwReason == DLL_PROCESS_ATTACH) { DetourTransactionBegin(); DetourUpdateThread(GetCurrentThread()); DetourAttach(&(PVOID&)TrueSleep, TimedSleep); DetourTransactionCommit(); } else if (dwReason == DLL_PROCESS_DETACH) { DetourTransactionBegin(); DetourUpdateThread(GetCurrentThread()); DetourDetach(&(PVOID&)TrueSleep, TimedSleep); DetourTransactionCommit(); } return TRUE; }

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• Web Workers - Transferable Objects for JSON

  - by kclem06

  HTML 5 Web workers are very slow when using worker.postMessage on a large JSON object. I'm trying to figure out how to transfer a JSON Object to a web worker - using the 'Transferable Objects' types in Chrome, in order to increase the speed of this. Here is what I'm referring to and appears it should speed this up quite a bit: http://updates.html5rocks.com/2011/12/Transferable-Objects-Lightning-Fast I'm having trouble finding a good example of this (and I don't believe I want to use an ArrayBuffer). Any help would be appreciated. I'm imagining something like this: worker = new Worker('workers.js'); var large_json = {}; for(var i = 0; i < 20000; ++i){ large_json[i] = i; large_json["test" + i] = "string"; }; //How to make this call to use Transfer Objects? Takes approx 2 seconds to serialize this for me currently. worker.webkitPostMessage(large_json);

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• How can I change the text in a <span></span> element using jQuery?

  - by Eric Reynolds

  I have a span element as follows: <span id="download">Download</span>. This element is controlled by a few radio buttons. Basically, what I want to do is have 1 button to download the item selected by the radio buttons, but am looking to make it a little more "flashy" by changing the text inside the <span> to say more specifically what they are downloading. The span is the downloading button, and I have it animated so that the span calls slideUp(), then should change the text, then return by slideDown().Here is the code I am using that does not want to work. $("input[name=method]").change(function() { if($("input[name=method]").val() == 'installer') { $('#download').slideUp(500); $('#download').removeClass("downloadRequest").removeClass("styling").css({"cursor":"default"}); $('#download').text("Download"); $('#download').addClass("downloadRequest").addClass("styling").css({"cursor":"pointer"}); $('#download').slideDown(500); } else if($("input[name=method]").val() == 'url') { $('#download').slideUp(500); $('#download').removeClass("downloadRequest").removeClass("styling").css({"cursor":"default"}); $('#download').text("Download From Vendor Website"); $('#download').addClass("styling").addClass("downloadRequest").css({"cursor":"pointer"}); $('#download').slideDown(500); } }); I changed the code a bit to be more readable so I know that it doesn't have the short code that jQuery so eloquently allows. Everything in the code works, with the exception of the changing of the text inside the span. I'm sure its a simple solution that I am just overlooking. Any help is appreciated, Eric R.

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• documenting class attributes

  - by intuited

  I'm writing a lightweight class whose attributes are intended to be publicly accessible, and only sometimes overridden in specific instantiations. There's no provision in the Python language for creating docstrings for class attributes, or any sort of attributes, for that matter. What is the accepted way, should there be one, to document these attributes? Currently I'm doing this sort of thing: class Albatross(object): """A bird with a flight speed exceeding that of an unladen swallow. Attributes: """ flight_speed = 691 __doc__ += """ flight_speed (691) The maximum speed that such a bird can attain. """ nesting_grounds = "Raymond Luxury-Yacht" __doc__ += """ nesting_grounds ("Raymond Luxury-Yacht") The locale where these birds congregate to reproduce. """ def __init__(**keyargs): """Initialize the Albatross from the keyword arguments.""" self.__dict__.update(keyargs) Although this style doesn't seem to be expressly forbidden in the docstring style guidelines, it's also not mentioned as an option. The advantage here is that it provides a way to document attributes alongside their definitions, while still creating a presentable class docstring, and avoiding having to write comments that reiterate the information from the docstring. I'm still kind of annoyed that I have to actually write the attributes twice; I'm considering using the string representations of the values in the docstring to at least avoid duplication of the default values. Is this a heinous breach of the ad hoc community conventions? Is it okay? Is there a better way? For example, it's possible to create a dictionary containing values and docstrings for the attributes and then add the contents to the class __dict__ and docstring towards the end of the class declaration; this would alleviate the need to type the attribute names and values twice. edit: this last idea is, I think, not actually possible, at least not without dynamically building the class from data, which seems like a really bad idea unless there's some other reason to do that. I'm pretty new to python and still working out the details of coding style, so unrelated critiques are also welcome.

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• Passing arguments to objects created using the new operator?

  - by Abhijit

  Hi guys, I have a small C++ problem to which I don't know the best solution. I have two classes A and B as follows: class A { int n; B* b; public: A(int num): n(num) { b = new B[n]; for (int i = 0; i < n; i++) { b[i].setRef(this); } } ~A() { delete [] b; } }; class B { A* a; public: B() { } B(A* aref) { a = aref; } void setRef(A* aref) { a = aref; } }; I am creating an object of class A by passing to its constructor the number of objects of class B I want to be created. I want every object of class B to hold a pointer to the class A object that creates it. I think the best way to do this would be by passing the pointer to the class A object as a constructor argument to the class B object. However, since I'm using the new operator, the no-args constructor for class B is called. As a result, the only solution I can see here is calling the setRef(A*) method for every object of class B after it has been constructed using the new operator. Is there a better solution/design pattern that would be more applicable here? Would using placement new for class B be a better solution? Thanks in advance for your help.

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• documenting class properties

  - by intuited

  I'm writing a lightweight class whose properties are intended to be publicly accessible, and only sometimes overridden in specific instantiations. There's no provision in the Python language for creating docstrings for class properties, or any sort of properties, for that matter. What is the accepted way, should there be one, to document these properties? Currently I'm doing this sort of thing: class Albatross(object): """A bird with a flight speed exceeding that of an unladen swallow. Properties: """ flight_speed = 691 __doc__ += """ flight_speed (691) The maximum speed that such a bird can attain """ nesting_grounds = "Throatwarbler Man Grove" __doc__ += """ nesting_grounds ("Throatwarbler Man Grove") The locale where these birds congregate to reproduce. """ def __init__(**keyargs): """Initialize the Albatross from the keyword arguments.""" self.__dict__.update(keyargs) Although this style doesn't seem to be expressly forbidden in the docstring style guidelines, it's also not mentioned as an option. The advantage here is that it provides a way to document properties alongside their definitions, while still creating a presentable class docstring, and avoiding having to write comments that reiterate the information from the docstring. I'm still kind of annoyed that I have to actually write the properties twice; I'm considering using the string representations of the values in the docstring to at least avoid duplication of the default values. Is this a heinous breach of the ad hoc community conventions? Is it okay? Is there a better way? For example, it's possible to create a dictionary containing values and docstrings for the properties and then add the contents to the class __dict__ and docstring towards the end of the class declaration; this would alleviate the need to type the property names and values twice. I'm pretty new to python and still working out the details of coding style, so unrelated critiques are also welcome.

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• Boost::Mutex & Malloc

  - by M. Tibbits

  Hi all, I'm trying to use a faster memory allocator in C++. I can't use Hoard due to licensing / cost. I was using NEDMalloc in a single threaded setting and got excellent performance, but I'm wondering if I should switch to something else -- as I understand things, NEDMalloc is just a replacement for C-based malloc() & free(), not the C++-based new & delete operators (which I use extensively). The problem is that I now need to be thread-safe, so I'm trying to malloc an object which is reference counted (to prevent excess copying), but which also contains a mutex pointer. That way, if you're about to delete the last copy, you first need to lock the pointer, then free the object, and lastly unlock & free the mutex. However, using malloc to create a boost::mutex appears impossible because I can't initialize the private object as calling the constructor directly ist verboten. So I'm left with this odd situation, where I'm using new to allocate the lock and nedmalloc to allocate everything else. But when I allocate a large amount of memory, I run into allocation errors (which disappear when I switch to malloc instead of nedmalloc ~ but the performance is terrible). My guess is that this is due to fragmentation in the memory and an inability of nedmalloc and new to place nice side by side. There has to be a better solution. What would you suggest?

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