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• Extracting a reference from a c++ vector

  - by Archanimus

  Hello folks, I have a vector< vector< vector< int and I would like to extract from it a vector< vector< int to process it individually. The problem is that when I write : myMatrix = myCube[anIndex]; the matrix is copied but I only want a reference in order to save memory. Can you please help me out ? Thanks a lot!

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• Reason for .Net UI Element Thread-restriction

  - by Charles Bretana

  We know that it is not possible to execute code that manipulates the properties of any UI element from any thread other than the thread the element was instantiated on... My question is why? I remember that when we used COM user interface elements, (in COM/VB6 days), that all UI elements were created using COM classes and co-classes that stored their resources using a memory model referred to as Thread-Local-Storage (TLS) , but as I recall, this was required because of something relaetd to the way COM components were constructed, and should not be relevant to .Net UI elements. Wha's the underlying reason why this restriction still exists? Is it because the underlying Operating System still uses COM-based Win32 API classes for all UI elements, even the ones manipulated in a managed .Net application ??

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• Why don't hardware failures show up at the programming language level?

  - by Julian Cienfuegos

  I am wondering if anyone can give my a good answer, or at least point me in the direction of a good reference to the following question: How come I have never heard of a computer breaking in a very fundamental way? How come when I declare x to be a double it stays as a double? How come there is never a short circuit that robs it of some bytes and makes it an integer? Why do we have faith that when we initialize x to 10, there will never be a power surge that will cause it to become 11, or something similar? I think I need a better understanding of memory. Thanks, and please don't bash me over the head for such a simple/abstract question.

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• Android app crashes on second run

  - by Nick

  I have been working on my app and it runs on the simulator fine. I loaded it into my phone and now I have a problem. It runs fine when I first start it and also if I pick home and then restart it; however, if I use the back arrow and then restart it it crashes on that time, but will work out the next time I start it. I think it has to do with some kind of memory build up, but I verified onDestroy is being called, I figured that deletes everything my program created, right?

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• merge three file into one big file

  - by davit-datuashvili

  suppose that we have three array int a[]=new int[]{4,6,8,9,11,12}; int b[]=new int[]{3,5,7,13,14}; int c[]=new int[]{1,2,15,16,17}; and we want to merge it into one big d array where d.length=a.length+b.length+c.length but we have memory problem it means that we must need use only this d array where we should merge these these three array of course we can use merge sort but can we use merge algorithm without sorting method? like two sorted array we can merge in one sorted array what about three or more array?

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• Reason for different segments in Linux on x86

  - by anjruu

  Hey all, So, I know that Linux uses four default segments for an x86 processor (kernel code, kernel data, user code, user data), but they all have the same base and limit (0x00000000 and 0xfffff), meaning each segment maps to the same set of linear addresses. Given this, why even have user/kernel segments? I understand why there should be separate segments for code and data (just due to how the x86 processor deals with the cs and ds registers), but why not have a single code segment and a single data segment? Memory protection is done through paging, and the user and kernel segments map to the same linear addresses anyway. Thanks! anjruu

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• Does a servlet-based stack have significant overheads?

  - by John

  I don't know if it's simply because page-loads take a little time, or the way servlets have an abstraction framework above the 'bare metal' of HTTP, or just because of the "Enterprise" in Jave-EE, but in my head I have the notion that a servlet-based app is inherently adding overhead compared to a Java app which simply deals with sockets directly. Forget web-pages, imagine instead a Java server app where you send it a question over an HTTP request and it looks up an answer from memory and returns the answer in the response. You can easily write a Java socket-based app which does this, you can also do a servlet approach and get away from the "bare metal" of sockets. Is there any measurable performance impact to be expected implementing the same approach using Servlets rather than a custom socket-based HTTP listening app? And yes, I am hazy on the exact data sent in HTTP requests and I know it's a vague question. It's really about whether servlet implementations have lots of layers of indirection or anything else that would add up to a significant overhead per call, where by significant I mean maybe an additional 0.1s or more.

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• Can I make a pointer to the code, and pass to the next instruction?

  - by drigoSkalWalker

  Like this link http://gcc.gnu.org/onlinedocs/gcc-3.3.1/gcc/Labels-as-Values.html I can get the memory address of an label, so if I declare a label, get your address, and add your address, i will pass to next instruction? some ilustration int main () { void *ptr; label: instruction 1; instruction 2; ptr = &&label; // So if I do it... ptr = ptr + 1; // I will get the instruction 2 correct?? Thanks for all answers.

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• What are the disadvantages of using a StringBuilder?

  - by stickman

  I know that StringBuilder is more efficient than a normal string when processing code which modifies the string value a lot because although strings act like value types, they are actually reference, which makes them immutable so every time we change it, we need to create a new reference in memory. My question is that, why doesn't .NET just use stringBuilder by default? There must be some disadvantages of it over just using String. Can anyone tell me what they are? The only thing I can think of is perhaps it is a heavier object and it takes more time to instantiate so if you aren't changing the string too much, this would override the benefits of StringBuilder

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• What Happens if i create a byte array continuously in a while loop with different size and add read an stream into it?

  - by SajidKhan

  I want to read an audio file into multiple byte arrays , with different size . And then add into a shared memory. What will happen if use below code. Does the byte array gets over written. I understand it will creat multiple byte array , how do i erase those byte arrays after my code does what it needs to do. int TotalBuffer = 10; while (TotalBuffer !=0){ bufferData = new byte[AClipTextFileHandler.BufferSize.get(j)]; input.read(bufferData); Sharedbuffer.put(bufferData); i++; j++; TotalBuffer--; }

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• What is the result of "new int[ 0 ]"? [closed]

  - by ArunSaha

  Possible Duplicates: What does zero-sized array allocation do/mean? C++ new int[0] — will it allocate memory? int * p; p = new int[ 0 ]; What is the expected outcome when new is called for zero number of elements? Is the outcome defined or undefined? Further, is it okay to call delete [] p; on that pointer? What is the intuition/analogy to this situation of pointer to an array of zero elements? Thanks in advance. Regards, Arun

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• Response Time is different for mulitiple execution of the application with the same request Performa

  - by sivananda

  My java application functionality is to provide reference data (basically loads lots of data from xml files into hashmap) and hence we request for one such data from the hashmap based on a id and we have such multiple has map for different set of business data. The problem is that when i tried executing the java application for the same request multiple times, the response times are different like 31ms, 48ms, 72ms, 120ms, 63ms etc. hence there is a considerable gap between the min and max time taken for the execution to complete. Ideally, i would expect the response times to be like, 63ms, 65ms, 61ms, 70ms, 61ms, but in my case the variation of the response time for the same request is varying hugely. I had used a opensource profile to understand if there is any extra execution of the methods or memory leak, but as per my understanding there was no problem. Please let me know what could be the reasons and how can i address this problem.

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• C# array problem

  - by user208080

  Hi there. I am a newbie in C# and here are 2 questions: I have a 2d array a[3,3], how can I express one dimension as a new array and pass to some function. i.e. int[,] a = new int[3,3]; a[0,0] = 1; ... string b = concatenate(a[0]); // where concatenate is a function take a one dimension array as param Can I create a 65000x65000 array with C#? I got some "out of memory" error. Thanks in advance.

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• In Perl, can I limit the length of a line as I read it in from a file (like fgets)

  - by SB

  I'm trying to write a piece of code that reads a file line by line and stores each line, up to a certain amount of input data. I want to guard against the end-user being evil and putting something like a gig of data on one line in addition to guarding against sucking in an abnormally large file. Doing $str = <FILE> will still read in a whole line, and that could be very long and blow up my memory. fgets lets me do this by letting me specify a number of bytes to read during each call and essentially letting me split one long line into my max length. Is there a similar way to do this in perl? I saw something about sv_gets but am not sure how to use it (though I only did a cursory Google search). Thanks.

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• PHP find if file data is an image

  - by Christian Sciberras

  Imagine I have some file data in a variable $data. I need to determine whether it is an image or not. No need for details such as corrupt images etc. Firs thought would be getting the file mime type by looking at the magic number and then see whether "image" is in the mime type. No such luck, even if I have a "file extension to mime type" script, I don't have a reliable way to get mime from magic number. My next option was to have a reasonable list of image file magic numbers and consult them. However, it relatively difficult to find such magic numbers (gif for instance has different magic numbers, some of which could pretty rare - if memory serves me right). A better idea would be some linux program which can do this kind of thing. Any ideas? I'm running RHEL and PHP 5.3. I've got root access - ie able to install stuff if needed. - Chris.

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• Why does C++ linking use virtually no CPU? (updated)

  - by John

  On a native C++ project, linking right now can take a minute or two, yet during this time CPU drops from 100% during compilation to virtually zero. Does this mean linking is primarily a disk activity? If so, is this the main area an SSD would make big changes? But, why aren't all my OBJ files (or as many as possible) kept in RAM after compilation to avoid this? With 4Gb of RAM I should be able to save a lot of disk access and make it CPU-bound again, no? update: so the obvious follow-up is, can VC++ compiler and linker talk together better to streamline things and keep OBJ files in memory, similar to how Delphi does?

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• Returning the address of local or temporary variable

  - by Dave18

  #include <iostream> int& foo() { int i = 6; std::cout << &i << std::endl; return i; } int main() { int i = foo(); std::cout << &i << std::endl; } I know it doesn't return the address of local variable so that is why the warning but why does it still works and assign the variable i in main() to '6'? How does it only return the value if the variable the was removed from stack memory?

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• C++ MFC how to compare LPCTSTR in a if statement?

  - by user1078510

  I have the following code: LPCTSTR strPermission = Method(); if (strPermission == L"0") { return true; } else { return false; } While debugging I can see that strPermission does equal "0", yet when I compare it like in the if statement it always returns false. The only thing I can think of is that it is comparing the memory address of the variable rather than the variable value. How do I compare strPermission to L"0" so that it would return true if strPermission equals "0". Thank you!

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• Reading a bmp file and inverting it in C

  - by user1763396

  I have an assignment that deals with reading a bmp file into memory, inverts the pixels, and then saves the inverted image to a new file. From this description it seems fairly easy, however I don't think my professor did a great job in explaining the necessary steps to go about doing so. He taught us about fread and fwrite but there is so much more. Can anyone explain the process in going about this problem (I'm no looking for a direct answer just an explanation). Here is the link to the problem's description: https://engineering.purdue.edu/OOSD/F2012/Exercises/ex5.html Thanks in advance for any sort of help. NOTE: I actually have looked into this problem but since I don't have a good standing on this info it's not quite "clicking".

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• Speed of running a test suite in Rails

  - by Milan Novota

  I have 357 tests (534 assertions) for my app (using Shoulda). The whole test suite runs in around 80 seconds. Is this time OK? I'm just curious, since this is one of my first apps where I write tests extensively. No fancy stuff in my app. Btw.: I tried to use in memory sqlite3 database, but the results were surprisingly worse (around 83 seconds). Any clues here? I'm using Macbook with 2GB of RAM and 2GHz Intel Core Duo processor as my development machine.

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• Does the Internet make us less good programmers? [closed]

  - by stagas

  With all the information and code available nowadays on the Internet has that diminished our capability of remembering or learning stuff just because we know they're available somewhere out there, just a Google away or a StackOverflow question away? For example I find myself visiting php.net quite often to check the syntax of the same functions over and over again, not because my memory sucks, but I don't feel like keeping the information in me, since I know I'll find it again on the net. And about StackOverflow, isn't the process of figuring things out on your own supposed to improve your programming skills? If the answers are all just clicks away, do we actually learn something or just keep a pointer in our heads where to search for it again when we need it? Your thoughts are welcome. Hope it doesn't shut down as subjective or anything, the answers would be really interesting ;)

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• Efficient questions

  - by rayman

  Hi, I have to manage xml's and Strings in my app. by efficenty and memory saving, is collection(ArrayList) will be much more 'expensive' then array of Strings? another issue is: i could use the content as regular String, or XML.. is working with XML also makes it more 'expensive' ? when i say i expensive i talk about taking system sources. please tell me by any of your exprience if the diffrences are significant? thanks, ray.

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• Good way to send a large file over a network in C#?

  - by BFreeman

  I am trying to build an application that can request files from a service running on another machine in the network. These files can be fairly large (500mb + at times). I was looking into sending it via TCP but I'm worried that it may require that the entire file be stored in memory. There will probably only be one client. Copying to a shared directory isn't acceptable either. The only communication required is for the client to say "gimme xyz" and the server to send it (and whatever it takes to ensure this happens correctly). Any suggestions?

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• Volatile keyword

  - by Tiyoal

  Say I have two threads and an object. One thread assigns the object: public void assign(MyObject o) { myObject = o; } Another thread uses the object: public void use() { myObject.use(); } Does the variable myObject have to be declared as volatile? I am trying to understand when to use volatile and when not, and this is puzzling me. Is it possible that the second thread keeps a reference to an old object in its local memory cache? If not, why not? Thanks a lot.

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• Find node level in a tree

  - by Álvaro G. Vicario

  I have a tree (nested categories) stored as follows: CREATE TABLE `category` ( `category_id` int(10) unsigned NOT NULL AUTO_INCREMENT, `category_name` varchar(100) NOT NULL, `parent_id` int(10) unsigned DEFAULT NULL, PRIMARY KEY (`category_id`), UNIQUE KEY `category_name_UNIQUE` (`category_name`,`parent_id`), KEY `fk_category_category1` (`parent_id`,`category_id`), CONSTRAINT `fk_category_category1` FOREIGN KEY (`parent_id`) REFERENCES `category` (`category_id`) ON DELETE SET NULL ON UPDATE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_spanish_ci I need to feed my client-side language (PHP) with node information (child+parent) so it can build the tree in memory. I can tweak my PHP code but I think the operation would be way simpler if I could just retrieve the rows in such an order that all parents come before their children. I could do that if I knew the level for each node: SELECT category_id, category_name, parent_id FROM category ORDER BY level -- No `level` column so far :( Can you think of a way (view, stored routine or whatever...) to calculate the node level? I guess it's okay if it's not real-time and I need to recalculate it on node modification.

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