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• read successive frames OpenCV using cvQueryframe

  - by AtharvaI

  Hi all I have a basic question in regards to cvQueryFrame() in OpenCV. I have the following code: IplImage *frame1,*frame2; frame1 = cvQueryFrame(capture); frame2 = cvQueryFrame(capture); Now my question is: if frame1 is a pointer to the first frame, is frame2 a pointer to the 2nd frame? So will the two cvQueryFrame() calls read successive frames? I thought I'd check myself first but the pointers frame1,frame2 seem to have the same hex value. :s I just need to capture two frames at a time and then need to process them. Thanks in advance

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• PHP , What is the difference between fopen r+ and r ! does it matter if i used r+ when not intending

  - by Naughty.Coder

  when I use fopen function , why don't I use r+ always , even when I'm not going to write any thing ... is there a reason for separating writing/reading process from only reading .. like , the file is locked for reading when I use r+ , because i might write new data into it or something ... another question : in php manual a+ : Open for reading and writing; place the file pointer at the end of the file. If the file does not exist, attempt to create it. What is supposed to be read if you are at the end of the file ..(pointer at the end) !!? where to learn more about the filesystem thing .... it's confusing

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• Passing arguments to UILabel [ 2 ] *

  - by DesperateLearner

  I'm trying to call a method of the below (Scroll animation class) type from a viewcontroller class. -(void)CreateLabel:(CGRect )frame andLabel:(UILabel *[NUM_LABELS])label andview:(UIView *)view; I got some errors when I tried passing the argument. Any suggestion on how to call this? This is how I called that method ScrollAnimation *newAnimation = [[ScrollAnimation alloc] init]; [newAnimation CreateLabel:CGRectMake(0, 50, 300,30) andLabel:animateLabel[NUM_LABELS] andview:self.view]; I have the error /Volumes/Red Drive/CarTransition/CarTransition/ViewController.m:120:66: Implicit conversion of an Objective-C pointer to 'UILabel **' is disallowed with ARC /Volumes/Red Drive/CarTransition/CarTransition/ViewController.m:120:66: Incompatible pointer types sending 'UILabel *__strong' to parameter of type 'UILabel **'

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• C++ DWORD* to BYTE*

  - by NomeSkavinski

  My issue, i am trying to convert and array of dynamic memory of type DWORD to a BYTE. Fair enough i can for loop through this and convert the DWORD into a BYTE per entry. But is their a faster way to do this? to take a pointer to DWORD data and convert the whole piece of data into a pointer to BYTE data? such as using a memcpy operation? I feel this is not possible, im not requesting an answer just an experienced opinion on my approach, as i have tried testing both approaches but seem to fail getting to a solution on my second solution. Thanks for any input, again no answers just a point in the right direction. Nor is this a homework question, i felt that had to be mentioned.

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• mysql stored routine vs. mysql-alternative?

  - by user522962

  We are using a mysql database w/ about 150,000 records (names) total. Our searches on the 'names' field is done through an autocomplete function in php. We have the table indexed but still feel that the searching is a bit sluggish (a few full seconds vs. something like Google Finance w/ near-instant response). We came up w/ 2 possibilities, but wanted to get more insight: Can we create a bunch (many thousands or more) of stored procedures to speed up searches, or will creating that many stored procedures bog-down the db? Is there a faster alternative to mysql for "select" statements (speed on inserting & updating rows isn't too important so we can sacrifice that, if necessary). I've vaguely heard of BigTable & others that don't support JOIN statements....we need JOIN statements for some of our other queries we do. thx

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• How is push()ing and pop()ping defined?

  - by Helper Method

  I know how the push() and pop() methods in a typical implementation of a Queue/Linked List work but what I do want to know is what you actually define as a push or a pop? When can you name a method push()/pop()? What makes the insert()/add() method in a typical Tree implementation not a push()? My understanding is that push()ing means putting something to a position some special pointer is pointing to, and pop()ping an element means putting some object away some pointer is pointing to, but it doesn't seem to be clearly defined. Or does the naming matter at all?

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• PHP HTML to PDF free convertor Resources

  - by Diarmuid

  Hi All, What is the best PHP HTML to PDF free converter around, not just in terms of functionality but also in terms of resource usage and speed Thanks

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• Regarding C typedef struct

  - by Bruce Duncan

  I have multiple instances of typedef struct box so box box1, box box2 etc. The members of the struct are length, width, height etc. typedef struct { int width; int height; } box; box box1; box box2; How can I create a function that operates on all the width members of each box instance? My confusion is how do I pass a pointer to a typedef struct member that works across all instances of box. I know how to pass a pointer to a specific instance member like box1.width but how to pass .width and then do box1.width=value; box2.width=value; box3.width=value; within the function?

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• Record Name field in DNS responce

  - by Lescott

  I just read about DNS protocol, and found, that the name field can be writen in two ways: lenght of the next label the label lenght of the next label the label ... zero-byte pointer to the previous name field Next is the original article fragment: The Resource Record Name field is encoded in the same way as the Question Name field unless the name is already present elsewhere in the DNS message, in which case a 2-byte field is used in place of a length-value encoded name and acts as a pointer to the name that is already present. So, my question is, how can I determine the first or the second way is using in a package?

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• C++ STL: Array vs Vector: Raw element accessing performance

  - by oh boy

  I'm building an interpreter and as I'm aiming for raw speed this time, every clock cycle matters for me in this (raw) case. Do you have any experience or information what of the both is faster: Vector or Array? All what matters is the speed I can access an element (opcode receiving), I don't care about inserting, allocation, sorting, etc. I'm going to lean myself out of the window now and say: Arrays are at least a bit faster than vectors in terms of accessing an element i. It seems really logical for me. With vectors you have all those security and controlling overhead which doesn't exist for arrays. (Why) Am I wrong? No, I can't ignore the performance difference - even if it is so small - I have already optimized and minimized every other part of the VM which executes the opcodes :)

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• How to pass a member function to a function used in another member function?

  - by Tommaso Ferrari

  I found something about my problem, but I don't already understand very well. I need to do something like this: class T{ double a; public: double b; void setT(double par){ a=par; }; double funct(double par1) { return par1/a; } void exec(){ b=extfunct(funct, 10); } } double extfunct(double (*f)(double),double par2){ return f(par2)+5; } Operation and function are only for example, but the structure is that. The reason of this structure is that I have a precostituited class which finds the minimum of a gived function (it's extfunct in the example). So I have to use it on a function member of a class. I understood the difference between pointer to function and pointer to member function, but I don't understand how to write it. Thanks, and sorry for the poor explanation of the problem.

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• Is there any way that I can draw fast a chart with too many series? [on hold]

  - by Maryam Bagheri

  I have a project that need to draw a fast chart with many series. I must change start position of drawing to a favor position when user want. .Net Chart is slow in lots of series. I wanted to use this library: http://www.codeproject.com/Articles/32836/A-simple-C-library-for-graph-plotting?msg=4109664#xx4109664xx but loading speed is too slow when count of series increases. When I plot the chart, I must invalidate the chart for updates, drawing speed will be too slow if there are too many series. I need at least 900 series in a chart for this project. I wanted to use multiple layer series to decrease invalidate rate with the idea: http://www.codeproject.com/Articles/84833/Drawing-multiple-layers-without-flicker I do not know this idea would be helpful. I tested LightningChart control but it could not help me.

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• What is wrong with my version of strchr?

  - by Eduard Saakashvili

  My assignment is to write my own version of strchr, yet it doesn't seem to work. Any advice would be much appreciated. Here it is: char *strchr (const char *s, int c) //we are looking for c on the string s { int dog; //This is the index on the string, initialized as 0 dog = 0; int point; //this is the pointer to the location given by the index point = &s[dog]; while ((s[dog] != c) && (s[dog] != '\0')) { //it keeps adding to dog until it stumbles upon either c or '\0' dog++; } if (s[dog]==c) { return point; //at this point, if this value is equal to c it returns the pointer to that location } else { return NULL; //if not, this means that c is not on the string } }

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• performance issue with a website.

  - by pradeep

  Hi, I have a website .. [SPAM LINK REMOVED]. When you see pages like [SPAM LINK REMOVED] and [SPAM LINK REMOVED]. These pages load a bit slowly in FF. Please see if the speed is reasonable or speed needs to improve and in IE 6 it takes ages to load the website. Please let me know what all should i do to increase the performance of website. I tried all the options given by firebug. But nothing much helped. If any1 can let me know where all i should take care to increase the performance it will be very helpful.

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• C++: Throwing shared_ptr of derived and catching shared_ptr of base?

  - by hasvn

  Ok, I've been told this problem: Why can you throw a pointer to a derived class and catch a pointer to its base... but you can't do that with shared_ptrs? Example, this works: class Base {}; class Derived : public Base {}; int main() { try { throw new Derived() ; } catch( const Base2 * b ) { printf("Received a base" ) ; } return 0 ; } But this doesn't int main() { try { throw std::tr1::shared_ptr<Derived>( new Derived() ) ; } catch( const std::tr1::shared_ptr<Base> & b ) { printf("Received a base" ) ; } return 0 ; } Any ideas?

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• Exception in C#

  - by user1803513

  I am facing null pointer exception in below code as it is happening very rarely and I tried to debug to replicate the issue but no luck. Can anybody help me what can cause null point exception here. private static void MyTaskCompletedCallback(IAsyncResult res) { var worker = (AsyncErrorDelegate)((AsyncResult)res).AsyncDelegate; var async = (AsyncOperation)asyncResult.AsyncState; worker.EndInvoke(res); lock (IsAsyncOpOccuring) { IsBusy = false; } var completedArgs = new AsyncCompletedEventArgs(null, false, null); async.PostOperationCompleted(e => OnTaskCompleted((AsyncCompletedEventArgs)e), completedArgs); } Null Pointer exception is reported at var async = (AsyncOperation)asyncResult.AsyncState;

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• SQL: Optimize insensive SELECTs on DateTime fields

  - by Fedyashev Nikita

  I have an application for scheduling certain events. And all these events must be reviewed after each scheduled time. So basically we have 3 tables: items(id, name) scheduled_items(id, item_id, execute_at - datetime) - item_id column has an index option. reviewed_items(id, item_id, created_at - datetime) - item_id column has an index option. So core function of the application is "give me any items(which are not yet reviewed) for the actual moment". How can I optimize this solution for speed(because it is very core business feature and not micro optimization)? I suppose that adding index to the datetime fields doesn't make any sense because the cardinality or uniqueness on that fields are very high and index won't give any(?) speed-up. Is it correct? What would you recommend? Should I try no-SQL? -- mysql -V 5.075 I use caching where it makes sence.

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• C# equivalent of recv?

  - by mlh

  Hello, I have a portion of C code that I am trying to port over to C#. In my C code, I create a socket and then issue a receive command. The receive command is void receive(mysocket, char * command_buffer) { recv(mysocket, command_buffer, COMMAND_BUFFER_SIZE, 0); } now, the command buffer is returned with new values including command_buffer[8] being a pointer to a string. I'm really confused as to how to do this in C# because C# Read() command specifically takes in bytes and not char. The important part is that I get the pointer to the string. Any ideas?

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• typedef to store pointers in C

  - by seriouslion

  The Size of pointer depends on the arch of the machine. So sizeof(int*)=sizeof(int) or sizeof(int*)=sizeof(long int) I want to have a custom data type which is either int or long int depending on the size of pointer. I tried to use macro #if, but the condition for macros does not allow sizeof operator. Also when using if-else, typedef is limited to the scope of if. if((sizeof(int)==sizeof(int *)){ typedef int ptrtype; } else{ typedef long int ptrtype; } //ptrtype not avialble here Is there any way to define ptrtype globally?

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• DAQ Triggers in Matlab

  - by RidePlanet

  I'm writing a program that detects the speed of a object by hall effect sensors that are run into MATLAB through a DAQ (MCC USB-1408FS) The problem that has arisen is that I'm using a non-stop scan technique to detect the state of one of 3 sensors. Unfortunately this means that unless the object is rotating past each sensor at the exact rate the program runs, I will see an instantaneous speed (done by comparing the time between two sensors) of zero. I need the sensors to signal the program to count when they are hit, instead of constantly scanning for the signal. How can this be done?

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• Level Order Successor of node in BST

  - by dsiap

  How can we find level order successor of a node in bst if parent pointer is given(with out using Queue ) ?

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• SQL Server - how to determine if indexes aren't being used?

  - by rwmnau

  I have a high-demand transactional database that I think is over-indexed. Originally, it didn't have any indexes at all, so adding some for common processes made a huge difference. However, over time, we've created indexes to speed up individual queries, and some of the most popular tables have 10-15 different indexes on them, and in some cases, the indexes are only slightly different from each other, or are the same columns in a different order. Is there a straightforward way to watch database activity and tell if any indexes are not hit anymore, or what their usage percentage is? I'm concerned that indexes were created to speed up either a single daily/weekly query, or even a query that's not being run anymore, but the index still has to be kept up to date every time the data changes. In the case of the high-traffic tables, that's a dozen times/second, and I want to eliminate indexes that are weighing down data updates while providing only marginal improvement.

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• Visual C++ CreateThread Parameter Problem

  - by Vanwaril

  I have a class that contains a function that calls create thread, and needs to pass itself (this) as a parameter: DWORD threadId; HANDLE h = CreateThread( NULL, 0, runThread, this, 0, &threadId); My runThread definition is as follows: DWORD WINAPI runThread(LPVOID args) { Obj *t = (Obj*)args; t->funct(); return 0; } Unfortunately, the object t that I get in runThread() gets garbage. My Obj class has a function pointer attribute. Could that be the problem? class Obj{ void(*funct)(); and in the constructor: Obj(void(*f)()) { funct = f; } where is my mistake? The function pointer, the createThread itself, or type-casting? I tried whatever I could think of.

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• Running a piece of code for a certain amount of time in C#?

  - by Hazem

  Hi I am working on a robot that is capable of motion detection using a webcam. I am doing this in C# The robot moves too fast, so I want to turn it on/off at short time intervals in order to reduce its speed. For example, it will start the engine then wait 0.5 second and turn it off, this cycle repeats every 2 seconds. This way, its speed wont be too fast. I would like to include this in a single function called Move() I just don't know how to do this, especially because my motion detection code runs like 20 times a second. Depending on the position of the obstacle, I may need to disable the Move() function and activate other functions that let the robot move into other directions. Any ideas/suggestions on where am I supposed to start? Thanks a lot!

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• Pointers and collection of pointers in C++. How to properly delete.

  - by Julen

  Hello, This is a newbe question but I have alwasy doubts with pointers in C++. This is the situation. I have a class A which as a collection (a vector actually) of pointers of class B. This same class A has another collection of pointers to class C. Finally the objects of class B have also a collection to pointers to class C which point to the same instances the class A points to. My question is, if I delete a member of class-C-type pointer in class B, what happens to the pointer in class A that points to the deleted instance of class C? How this situation has to be treated? Thanks a lot in advance! Julen.

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