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• Is there a way to read 10000 lines from a file in python?

  - by windsound

  I am relatively new in python, was working on C a lot. Since I was seeing so many new functions in python that I do not know, I was wondering if there is a function that can request 10000 lines from a file in python. Something like this is what I expect if that kind of function exist: lines = get_10000_lines(file_pointer) Did python have a build-in function or is there any module that I can download for this? If not, how do I do this to be easiest way. I need to analyze a huge file so I want to read 10000 lines and analyze per time to save memory. Thanks for helping!

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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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• Clone a 'link' in SWT

  - by Steve

  I have a table of information that includes a username, an ip address, and a timestamp. What I wanted to do was to have the ip address contained within a link object that when the link is clicked it utilizes bgp.he.net to get information about the host/IP address. I have tried creating threads to resolve the IP addresses but it is often a large amount of IP addresses and I read that InetAddress#getByName isn't non-blocking, so I figured having links that go to this site is the next best thing. Question is: Is it possible to have links for each of my IP addresses in the table without creating a new link object for each row? I don't know how bad that would be on memory usage which is why I'm inquiring about cloning an instance of an IP and having the link open bgp.he.net/link.getText()

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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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• 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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• 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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• 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/C++ function definitions without assembly

  - by Jack

  Hi, I always thought that functions like printf() are in the last step defined using inline assembly. That deep into stdio.h is burried some asm code that actually tells CPU what to do. Something like in dos, first mov bagining of the string to some memory location or register and than call some int. But since x64 version of Visual Studio doesent support inline assembler at all, it made me think that there are really no assembler-defined functions in C/C++. So, please, how is for example printf() defined in C/C++ without using assembler code? What actually executes the right software interrupt? Thanks.

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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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• Operations on 64bit words in 32bit system

  - by Vilo

  I'm new here same as I'm new with assembly. I hope that you can help me to start. I'm using 32bit (i686) Ubuntu to make programs in assembly, using gcc compiler. I know that general-purpose-registers are 32bit (4 bytes) max, but what when I have to operate on 64 bit numbers? Intel's instruction says that higher bits are stored in %edx and lower in %eax Great... So how can I do something with this 2-registers number? I have to convert 64bit dec to bin, then save it to memory and show on the screen. How to make the 64bit quadword at start of the program in .data section?

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• Trying to use tcl threads on windows 7 results in access violation.

  - by Juan

  I'm trying to get this simple program to work on windows, but it crashes: unsigned (__stdcall testfoo)(ClientData x) { return 0; } int main() { Tcl_ThreadId testid = 0; Tcl_CreateThread(&testid, testfoo, (ClientData) NULL, TCL_THREAD_STACK_DEFAULT, TCL_THREAD_NOFLAGS); } I am using a makefile generated by cmake and linking against a version of Tcl 8.5.7 I compiled myself using Visual C++ 2008 express. It was compiled using msvcrt,static,threads and the name of the resulting library is tcl85tsx.lib. The error is: Unhandled exception at 0x77448c39 in main.exe: 0xC0000005: Access violation writing location 0x00000014. The Tcl library works fine, and I can even run a threading script example by loading the Thread extension into it. My assumption is that there is something horribly wrong with a memory violation, but I have no idea what. Any help appreciated.

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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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• How do you ensure a mimetype in asp.net?

  - by Sem Dendoncker

  Hello, I have the following code to export a zip file: byte[] buffer = FileUtil.FileToByteArray(zipLocation, true); // push the memory data to the client. _ctx.Response.ContentType = "application/zip"; _ctx.Response.AddHeader("content-disposition", String.Format("attachment; filename={0}", String.Format("map{0}.zip", mapId))); _ctx.Response.BinaryWrite(buffer); This code works great. After every export I get a perfectly made zipfile. The problem however is that when I try to import it, the mimetype sometimes is "application/empty". Now I wonder how can I ensure that the mimetype is always added? Cheers, M.

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• Updating a database periodically with Java

  - by MSR

  I would like to perform updates to a MySQL database using two separate classes (that do different things) -- one doing so every 10 seconds, and the second every minute. I have a few gaps in my Java knowledge and I'm wondering what the best way to achieve it is. Importantly, if connectivity to the database is lost, I need reconnection attempts to occur indefinitely, and I'm guessing the use of Prepared Statements will make queries more efficient. Should the connection to the database be left open all the time or closed between the updates being run? Maybe I also need to think about clearing objects/resources out of memory if the class instances are going to be run indefinitely.

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• C# how to store those information?

  - by 5YrsLaterDBA

  I have a PrivilegeGroup table, a Privileges table and a link table because the PrivilegeGroup table and the Privileges table is a many to many relationship. I am thinking about load all contents of PrivilegeGroup table and Privilege table into memory from database at beginning when application started. I want to save them in a form easily to look up. Usually we will look up the PrivilegeCode via GroupId. Which structure is good for this purpose? array of list? dictionary?

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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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• Best way to have unique key over 500M varchar(255) records in mysql/innodb?

  - by taw

  I have url column with unique key over it - but its performance on updates is absolutely atrocious. I suspect that's because the index doesn't all fit in memory. So I was thinking, how about adding a column of md5(url) with 16 bytes of binary data and unique-keying that instead. What would be the best datatype for that? I'd love to be able to just see 32-character hex hash, while mysql would convert it to/from 16 binary bytes and index that, as programs using the database might have some troubles with arbitrary binary data that I'd rather avoid if possible (also I'm a bit afraid that mysql might get some strange ideas about character sets and for example overalocating storage for that by 3:1 because it thinks it might need utf8, how do I avoid that for cure?).

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• Forcing an app to run single core only?

  - by Kevin

  I have this strange issue with some third party DLL's. The third party provider references some open source DLL's that have a memory exception whenever I try to use a certain method. This issue does not appear when the app is run on a single core machine, but obviously we cannot assume a user will have that. Is there a way to force an app, or even better yet a referenced DLL to run on a single core? Any other way to possibly fix this? Getting the third party to rebuild the OS dll's is apparently out of the question (its a bit of a sore spot with me currently :) ) so I have to handle it myself or just forget about providing this functionality.

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• SWIG interface file questions

  - by morpheous

  I am writing a C/C++ extension module for other languages and I am using SWIG to generate the bindings. I have two questions Can I include more than 1 header file in the declaration part of the interface file e.g.: /* Declarations exposed to wrapper: */ > %{ > #define SWIG_FILE_WITH_INIT > #include "a.h" > #include "b.h" > #include "c.h" %} In all of the examples I have seen so far, after the header include declaration (as shown above), the functions declared in the header are then declared again in the interface file. Is this really necessary, as it means there are two copies of the function declarations that need to be maintained. Note: I can appreciate that some functions/methods declaration may need to be 'decorated' with the 'newobject' declaration so these obviously need to be in the interface file, to avoid memory leaks - however, I would have though that it would be sufficient to include the headers and then ONLY the declarations of the functions/methods that need to be declared with 'newobject' - is this recommended way of doing things?

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• Change url property of .sitemap

  - by user555209

  Hello I have multiple .sitemap xml defined with different providers. For one xml file, I want to change the url (append Customerid in the url) by taking the existing url in xml file. I want this to be changed when the page is loaded the first time. For eg one of my node is And I want to make it as I have read many articles online talking about changing node in memory but cant make it work. Any help would be appreciated. Not working with breadcrumbs or sitemapPath control.

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• How to run stored procedure 1000 times

  - by subt13

  I have a stored procedure that I'm using to populate a table with about 60 columns. I have genereated 1000 exec statements that look like this: exec PopulateCVCSTAdvancement 174, 213, 1, 0, 7365 exec PopulateCVCSTAdvancement 174, 214, 1, 0, 7365 exec PopulateCVCSTAdvancement 175, 213, 0, 0, 7365 Each time the stored procedure will be inserting anywhere from 1 to 3,000 records (usually around 2,000 records). The "server" is running desktop hardware with 4 gigs of available memory on a server OS. The problem I have is that after the first 10-15 executes of an average of 1-2 seconds each time, the next 10-15 seem to never finish. Am I doing this correctly? How should I do this? Thanks! Top 10 waiters: LAZYWRITER_SLEEP SQLTRACE_INCREMENTAL_FLUSH_SLEEP REQUEST_FOR_DEADLOCK_SEARCH XE_TIMER_EVENT FT_IFTS_SCHEDULER_IDLE_WAIT CHECKPOINT_QUEUE LOGMGR_QUEUE SLEEP_TASK BROKER_TO_FLUSH BROKER_TASK_STOP

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• Heap Error in C++

  - by BobAlmond

  Dear all, I'm a beginner programmer in C++. Recently, I'm working on image processing thing using C++. but I have some problem that I want to ask. Suppose I have some code as follow: for (int i=0;i<100000;i++) { int * a = new int[10000]; //do something delete [] a; } When I executed that code, I receive runtime error, Heap Error... Is there anything wrong with that code, I mean, can I allocate memory and release it in the same loop? Thanks in advance...

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• Showing a hidden form

  - by Arcadian

  Newb question: how do i show a from that have been hidden using this.Hide(); I have tried MainMenuForm.Show(); and this just says i need an object ref have tried: MainMenuForm frmMainMenu = new MainMenuForm(); frmMainMenu.Show(); which seems to show the appropriate form. but when you exit the app, it is still held in memory because it hasn't shown the form that was hidden, instead it has shown a new version of the form. in effect having 2 instances of the form (one hidden, one visible). whats the correct procedure here Thanks in advance

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• How to make an mutable C array for this data type?

  - by mystify

  There's this instance variable in my objective-c class: ALuint source; I need to have an mutable array of OpenAL Sources, so in this case probably I need a mutable C-array. But how would I create one? There are many questions regarding that: 1) How to create an mutable C-array? 2) How to add something to that mutable C-array? 3) How to remove something from that mutable C-array? 4) What memory management pitfalls must I be aware of? Must i free() it in my -dealloc method? And yes, I think this is something for the nice community wiki...

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• how to get stl map to construct/destruct inserted object only once.

  - by Alberto Toglia

  I have found a very prejudicial fact about stl maps. For some reason I cant get objects being inserted in the map to get constructed/destructed only once. Example: struct MyObject{ MyObject(){ cout << "constructor" << endl; } ~MyObject(){ cout << "destructor" << endl; } }; int main() { std::map<int, MyObject> myObjectsMap; myObjectsMap[0] = MyObject(); return 0; } returns: constructor destructor destructor constructor destructor If I do: typedef std::pair<int, MyObject> MyObjectPair; myObjectsMap.insert( MyObjectPair(0,MyObject())); returns: constructor destructor destructor destructor I'm inserting Objects responsible for their own memory allocation, so when destructed they'll clean themselves up, being destructed several times is causing me some trouble.

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