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• pointer and malloc [closed]

  - by gcc

  How many methods/ways are there taking input by using with pointer and dynamic memory? Input: 3 1 2 n k l 2 1 2 p 4 55 62 * # x (x is stop value, first input always integer) Example code: p=malloc(sizeof(int)); scanf("%d",&num_arrays); while(1) { scanf("%c",&(*(p+i))); if(*(p+i)=='x') break; ++i; } "3" is stored in num_arrays. The other input values are stored in pointer[array].

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• Understanding behaviour of read() and write()

  - by neo730

  hi i am a student and just start learning low level c programming.i tried to understand read() and write() methods with this program. #include <unistd.h> #include <stdlib.h> main() { char *st; st=calloc(sizeof(char),2);//allocate memory for 2 char read(0,st,2); write(1,st,2); } i was expecting that it would give segmentation fault when i would try to input more than 2 input characters.but when i execute program and enter " asdf " after giving " as " as output it executes "df" command. i want to know why it doesn't give segmentation fault when we assign more than 2 char to a string of size 2.and why is it executing rest(after 2 char)of input as command instead of giving it as output only? also reading man page of read() i found read() should give EFAULT error,but it doesn't. I am using linux.

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• java virtual machine - how does it allocate resources?

  - by Will

  I am testing the performance of a data streaming system that supports continuous queries. This is how it works: - There is a polling service which sends data to my system. - As data passes into the system, each query evaluates based on a window of the stream at the current time. - The window slides as data passes in. My problem is this, when I add more queries to the system, I should expect the throughput to decrease because it can't cope the data rate. However, I actually observe an increase in throughput. I can't understand why this is the case and I am guessing that it's something to do with the way the JVM allocates CPU, memory etc. Can anyone shed any light to my problem?

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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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• Annotation retention policy: what real benefit is there in declaring `SOURCE` or `CLASS`?

  - by watery

  I know there are three retention policies for Java annotations: CLASS: Annotations are to be recorded in the class file by the compiler but need not be retained by the VM at run time. RUNTIME: Annotations are to be recorded in the class file by the compiler and retained by the VM at run time, so they may be read reflectively. SOURCE: Annotations are to be discarded by the compiler. And although I understand their usage scenarios, I don't get why it is such an important thing to specify the retention policy that retention policies exist at all. I mean, why aren't all the annotations just kept at runtime? Do they generate so much bytecode / occupy so much memory that stripping those undeclared as RUNTIME does make that much difference?

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• Using temporary arrays to cut down on code - inefficient?

  - by tommaisey

  I'm new to c++ (and SO) so sorry if this is obvious. I've started using temporary arrays in my code to cut down on repetition and to make it easier to do the same thing to multiple objects. So instead of: MyObject obj1, obj2, obj3, obj4; obj1.doSomming(arg); obj2.doSomming(arg); obj3.doSomming(arg); obj4.doSomming(arg); I'm doing: MyObject obj1, obj2, obj3, obj4; MyObject* objs[] = {&obj1, &obj2, &obj3, &obj4}; for (int i = 0; i !=4; ++i) objs[i]->doSomming(arg); Is this detrimental to performance? Like, does it cause unnecessary memory allocation? Is it good practice? Thanks.

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• Any efficient way to read datas from large binary file?

  - by limi

  Hi, I need to handle tens of Gigabytes data in one binary file. Each record in the data file is variable length. So the file is like: <len1><data1><len2><data2>..........<lenN><dataN> The data contains integer, pointer, double value and so on. I found python can not even handle this situation. There is no problem if I read the whole file in memory. It's fast. But it seems the struct package is not good at performance. It almost stuck on unpack the bytes. Any help is appreciated. Thanks.

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• Can I load lots of data only once and use it on each request?

  - by eikes

  Is there a way to load a big data object into the memory, which usually has to be loaded at each request, only once? In Java you can instantiate an object in a servlet when this servlet is loaded, but once it's there you can use it in any request. Example is below. Can this be done in PHP? public class SampleServlet extends HttpServlet { private static HugeGraphObject hgo; public void init() { hgo = HugeGraphObjectFactory.get(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String param = request.getParameter("q"); response.getWriter().write(hgo.getSomeThing(param)); } }

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• construct a unique number for a string in java

  - by praveen

  We have a requirement of reading/writing more than 10 million strings into a file. Also we do not want duplicates in the file. Since the strings would be flushed to a file as soon as they are read we are not maintaining it in memory. We cannot use hashcode because of collisions in the hash code due to which we might miss a string as duplicate. Two other approaches i found in my googling: 1.Use a message digest algorithm like MD5 - but it might be too costly to calculate and store. 2.Use a checksum algorithm. [i am not sure if this produces a unique key for a string- can someone please confirm] Is there any other approach avaiable. Thanks.

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• get function address from name [.debug_info ??]

  - by user361190

  Hi, I was trying to write a small debug utility and for this I need to get the function/global variable address given its name. This is built-in debug utility, which means that the debug utility will run from within the code to be debugged or in plain words I cannot parse the executable file. Now is there a well-known way to do that ? The plan I have is to make the .debug_* sections to to be loaded into to memory [which I plan to do by a cheap trick like this in ld script] .data { *(.data) __sym_start = .; (debug_); __sym_end = .; } Now I have to parse the section to get the information I need, but I am not sure this is doable or is there issues with this - this is all just theory. But it also seems like too much of work :-) is there a simple way. Or if someone can tell upfront why my scheme will not work, it ill also be helpful. Thanks in Advance, Alex.

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• try finally block around every Object.Create?

  - by max

  Hi, I have a general question about best practice in OO Delphi. Currently, I but a try finally block around everywhere, where I create an object, to free that object after usage (to avoid memory leaks). E.g.: aObject := TObject.Create; try aOBject.AProcedure(); ... finally aObject.Free; end; instead of: aObject := TObject.Create; aObject.AProcedure(); .. aObject.Free; To you think, it is good practice, or too much overhead? And what about the performance?

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• Best way to handle different panels occupying same area

  - by gmnnn

  I have this application: I want to change the marked area when the user is clicked one of the navBarItems (like Microsoft OUTLOOK). I've been doing some research and a lot of people said that I can add several panels and show/hide them when user is clicked a navBarItem. But the area will contain a lot of gridviews and a lot of other controls. I don't know if I want to initialize all of them when application starts because it's gonna be hard on the cpu and memory to keep all the controls running at the same time. And I don't think it's an elegant solution for this kind of situation. But if I choose to initialize controls when user is clicked to corresponding navBarItem, it's gonna be laggy for the user. What is the best design approach for this situation? PS: I can use commercial libraries too. Thank you.

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• Count of Distinct Int32 Values in .NET

  - by Eric J.

  I am receiving a stream of unordered Int32 values and need to track the count of distinct values that I receive. My thought is to add the Int32 values into a HashSet<Int32>. Duplicate entries will simply not be added per the behavior of HashSet. Do I understand correctly that set membership is based on GetHashCode() and that the hash code of an Int32 is the number itself? Is there an approach that is either more CPU or more memory efficient? UPDATE The data stream is rather large. Simply using Linq to iterate the stream to get the distinct count is not what I'm after, since that would involve iterating the stream a second time.

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• Is this a safe way to reference objects in JavaScript?

  - by John

  If I were to define two objects myDataStore and myDrawer something like this: var myDataStore = function(myObjectRef) { this.myInternalObject = myObjectRef; }; var myDrawer = function(myObjRef) { this.myInternalObject = myObjectRef; }; And if I were to create an object like so: (function(){ var myObject = window.myObject = function(){ this.dataStore = new myDataStore(this); this.drawer = new myDrawer(this); } })(); Then myObject.dataStore.myInternalObject, and myObject.drawer.myInternalObject, would simply be pointers back to the original 'myObject' - not taking up any additional memory in the browser. Yes? I am interested in implementing techniques like this - as it makes it easy for objects to communicate with each other.

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• Simple Java library for storing statistical observations and calculating statistics such as stddev,

  - by knorv

  For logging purposes I want to collect the response times of an external system, and periodically fetch various statistics (such as min/max/stddev) of the response times. I'm looking for a pure in-memory solution. What Java library can help me with this simple task? I'm looking for an API that would ideally look something along the lines of: StatisticsCollector s = new StatisticsCollector(); while (...) { double responseTime = ...; s.addObservation(responseTime); } double stddev = s.getStandardDeviation(); double mean = s.getMean();

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• Delegate Method only Firing after 5 or so Button Presses?

  - by CoDEFRo

  I'm having the most bizarre problem which I'm not even close to figuring out. I have a button which fires a delegate method. Once upon a time it was working fine, but after making some changes to my code, now the delegate method only fires after I push the button x amount of times (the changes I made to the code had nothing to do with the infrastructure that connects the delegate together). It varies, it can be 5 times to 10 times. I used the analyzer to check for memory leaks and there aren't any. There is too much code for me to paste here (I don't even know where to start or where the problem could be), but I'm wondering if anyone has experienced this problem before, or what could be causing it? This is very odd and have no clue what could be causing it.

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• Detecting when Javascript is performing poorly

  - by what-the-crap

  I'm working on a webapp in jquery that, on older machines or machines without much resources, may perform poorly. To get around this I'd like to make a degraded version that disables some of the features, particularly those that rely on large images. How can I tell if my app is running poorly on the user's computer in jquery or javascript in general? I just need a way to call a function that will degrade the app. (especially when the user may run low on system memory) The only way I can think of is for manual user intervention, but the option would add clutter for users that don't need it and users that do need it may not notice it. Thanks!

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• Javascript Image object without instantiating

  - by user276027

  This question is about javascript performance. Consider 3 examples for illustration: function loadImgA() { new Image().src="http://example.com/image.gif" } function loadImgA1() { Image().src="http://example.com/image.gif" } function loadImgB() { var testImg = new Image(); testImg.src="http://example.com/image.gif" } Now the point is I don't really need to manipulate the the image object after it was created, hence loadImgA(). The question is, what happens if nothing is assigned to the return value of the new Image() constructor - in that case I can actually skip the 'new' keyword as in loadImgA1()? Does the object then live outside the function or somehow affects memory usage? Other implications, differences? I reckon not, as no real instance was actually created? To put this into perspective, I only need to get the http request for image through. No preloading or other advanced image manipulation. What would be the preferred method from the above?

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• referencing struct fields in c with square brackets and an index instead of . and ->?

  - by lsiebert

  Assuming I have a structure such as: typedef struct { char * string1; char * string2; } TWO_WORDS; such that all the fields are of the same type, and my main has TWO_WORDS tw; can I reference string1 with tw[0] and string2 with two[1]? If so: is this part of the c standard? do i have to cast the struct to an array first? what about fields which are different sizes in memory what about fields which are different types but the same size? can you do pointer arithmetic within a structure? -

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• Java Basics: create class object

  - by user1767853

  In C++: class Rectangle { int x, y; public: void set_values (int,int); int area () {return (x*y);} }; int main () { Rectangle rect; rect.set_values (3,4); } In Java: class Rectangle { int x, y; void set_values (int x,int y); int area () {return (x*y);} } public static void main(String[] args) { Rectangle rect=new Rectangle(3,4); } In C++ compiler will create rect object & reserve memory 4 bytes. I want to know How Java is creating object?

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• bool - 255 value

  - by user994165

  I have this function defined: struct heap_validation { size_t num_alloc; size_t num_alloc_sz; struct memory *mem; }; ... bool get_isallocated(struct metadata_record *); When I call the heap_validation function from hashtable_traverse and print the result, I've gotten the following values: 0,255 ,246 void hashtable_traverse(struct metadata_record *metarec, struct heap_validation *heap_val) { printf("get_isallocated(metarec): %d\n",get_isallocated(metarec)); bool retrieved = false; bool allocated = get_isallocated(metarec); if (allocated) { heap_val->num_alloc += 1; I also tried with %d and I get the same result.

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• printf("... %c ...",'\0') and family - what will happen?

  - by SF.

  How will various functions that take printf format string behave upon encountering the %c format given value of \0/NULL? How should they behave? Is it safe? Is it defined? Is it compiler-specific? e.g. sprintf() - will it crop the result string at the NULL? What length will it return? Will printf() output the whole format string or just up to the new NULL? Will va_args + vsprintf/vprintf be affected somehow? If so, how? Do I risk memory leaks or other problems if I e.g. shoot this NULL at a point in std::string.c_str()? What are the best ways to avoid this caveat (sanitize input?)

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• A step-up from TiddlyWiki that is still 100% portable?

  - by Smandoli

  TiddlyWiki is a great idea, brilliantly implemented. I'm using it as a portable personal "knowledge manager," and these are the prize virtues: It travels on my USB flash memory stick and runs on any computer, regardless of operating system No software installation is needed on the computer (TiddlyWiki merely uses the Internet browser) No Internet connection is needed In terms of data retrieval functionality, it mimics a relational database (use of tags and internal links) Let's say I've got a million words of prose in 4,000 tiddlers (posts). I'm still testing, but it looks like TiddlyWiki gets very slow. Is there an app like TiddlyWiki that keeps all the virtues I listed above, and allows more storage? NOTE: Separation of content and presentation would be ideal. It's nifty that TiddlyWiki has everything in a single HTML document, but it's unhelpful in many ways. I don't care if a directory of assorted docs is needed (SQLite, XML?), as long as it's functionally self-contained.

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• The Oracle Enterprise Linux Software and Hardware Ecosystem

  - by sergio.leunissen

  It's been nearly four years since we launched the Unbreakable Linux support program and with it the free Oracle Enterprise Linux software. Since then, we've built up an extensive ecosystem of hardware and software partners. Oracle works directly with these vendors to ensure joint customers can run Oracle Enterprise Linux. As Oracle Enterprise Linux is fully--both source and binary--compatible with Red Hat Enterprise Linux (RHEL), there is minimal work involved for software and hardware vendors to test their products with it. We develop our software on Oracle Enterprise Linux and perform full certification testing on Oracle Enterprise Linux as well. Due to the compatibility between Oracle Enterprise Linux and RHEL, Oracle also certifies its software for use on RHEL, without any additional testing. Oracle Enterprise Linux tracks RHEL by publishing freely downloadable installation media on edelivery.oracle.com/linux and updates, bug fixes and security errata on Unbreakable Linux Network (ULN). At the same time, Oracle's Linux kernel team is shaping the future of enterprise Linux distributions by developing technologies and features that matter to customers who deploy Linux in the data center, including file systems, memory management, high performance computing, data integrity and virtualization. All this work is contributed to the Linux and Xen communities. The list below is a sample of the partners who have certified their products with Oracle Enterprise Linux. If you're interested in certifying your software or hardware with Oracle Enterprise Linux, please contact us via [email protected] Chip Manufacturers Intel, Intel Enabled Server Acceleration Alliance AMD Server vendors Cisco Unified Computing System Dawning Dell Egenera Fujitsu HP Huawei IBM NEC Sun/Oracle Storage Systems, Volume Management and File Systems 3Par Compellent EMC VPLEX FalconStor Fusion-io Hitachi Data Systems HP Storage Array Systems Lustre Network Appliance OCFS2 PillarData Symantec Veritas Storage Foundation Networking: Switches, Host Bus Adapters (HBAs), Converged Network Adapters (CNAs), InfiniBand Brocade Emulex Mellanox QLogic Voltaire SOA and Middleware ActiveState ActivePerl, ActivePython Tibco Zend Backup, Recovery & Replication Arkeia Network Backup Suite BakBone NetVault CommVault Simpana 8 EMC Networker, Replication Manager FalconStor Continuous Data Protector HP Data Protector NetApp Snapmanager Quest LiteSpeed Engine Steeleye Data Replication, Disaster Recovery Symantec NetBackup, Veritas Volume Replicator, Symantec Backup Exec Zmanda Amanda Enterprise Data Center Automation BMC CA Unicenter HP Server Automation (formerly Opsware), System Management Homepage Oracle Enterprise Manager Ops Center Quest Vizioncore vFoglight Pro TeamQuest Manager Clustering & High Availability FUJITSU x10sure NEC Express Cluster X Steeleye Lifekeeper Symantec Cluster Server Univa UniCluster Virtualization Platforms and Cloud Providers Amazon EC2 Citrix XenServer Rackspace Cloud VirtualBox VMWare ESX Security Management ArcSight: Enterprise Security Manager, Logger CA Access Control Centrify Suite Ecora Auditor FoxT Manager Likewise: Unix Account Management Lumension Endpoint Management and Security Suite QualysGuard Suite Quest Privilege Manager McAfee Application Control, Change ControlIntegrity Monitor, Integrity Control, PCI Pro Solidcore S3 Symantec Enterprise Security Manager (ESM) Tripwire Trusted Computer Solutions

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• Using PHP OCI8 with 32-bit PHP on Windows 64-bit

  - by christopher.jones

  The world migration from 32-bit to 64-bit operating systems is gaining pace. However I've seen a couple of customers having difficulty with the PHP OCI8 extension and Oracle DB on Windows 64-bit platforms. The errors vary depending how PHP is run. They may appear in the Apache or PHP log: Unable to load dynamic library 'C:\Program Files (x86)\PHP\ext\php_oci8_11g.dll' - %1 is not a valid Win32 application. or Warning oci_connect(): OCIEnvNlsCreate() failed. There is something wrong with your system - please check that PATH includes the directory with Oracle Instant Client libraries Other than IIS permission issues a common cause seems to be trying to use PHP with libraries from an Oracle 64-bit database on the same machine. There is currently no 64-bit version of PHP on http://php.net/ so there is a library mismatch. A solution is to install Oracle Instant Client 32-bit and make sure that PHP uses these libraries, while not interferring with the 64-bit database on the same machine. Warning: The following hacky steps come untested from a Linux user: Unzip Oracle Instant Client 32-bit and move it to C:\WINDOWS\SYSWOW64\INSTANTCLIENT_11_2. You may need to do this in a console with elevated permissions. Edit your PATH environment variable and insert C:\WINDOWS\SYSTEM32\INSTANTCLIENT_11_2 in the directory list before the entry for the Oracle Home library. Windows makes it so all 32-bit applications that reference C:\WINDOWS\SYSTEM32 actually see the contents of the C:\WINDOWS\SYSWOW64 directory. Your 64-bit database won't find an Instant Client in the real, physical C:\WINDOWS\SYSTEM32 directory and will continue to use the database libraries. Some of our Windows team are concerned about this hack and prefer a more "correct" solution that (i) doesn't require changing the Windows system directory (ii) doesn't add to the "memory" burden about what was configured on the system (iii) works when there are multiple database versions installed. The solution is to write a script which will set the 64-bit (or 32-bit) Oracle libraries in the path as needed before invoking the relevant bit-ness application. This does have a weakness when the application is started as a service. As a footnote: If you don't have a local database and simply need to have 32-bit and 64-bit Instant Client accessible at the same time, try the "symbolic" link approach covered in the hack in this OTN forum thread. Reminder warning: This blog post came untested from a Linux user.

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