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  • Can't inherit from auto_ptr without problems

    - by fret
    What I want to do is this: #include <memory> class autostr : public std::auto_ptr<char> { public: autostr(char *a) : std::auto_ptr<char>(a) {} autostr(autostr &a) : std::auto_ptr<char>(a) {} // define a bunch of string utils here... }; autostr test(char a) { return autostr(new char(a)); } void main(int args, char **arg) { autostr asd = test('b'); return 0; } (I actually have a copy of the auto_ptr class that handles arrays as well, but the same error applies to the stl one) The compile error using GCC 4.3.0 is: main.cpp:152: error: no matching function for call to `autostr::autostr(autostr)' main.cpp:147: note: candidates are: autostr::autostr(autostr&) main.cpp:146: note: autostr::autostr(char*) I don't understand why it's not matching the autostr argument as a valid parameter to autostr(autostr&).

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  • Why is 'volatile' parasitic in C++?

    - by Steve
    Consider the following code: int main() { int i; volatile int* p = &i; int *v = p; return 0; } This gives an error in g++: $ g++ -o volatile volatile.cpp volatile.cpp: In function ‘int main()’: volatile.cpp:6: error: invalid conversion from ‘volatile int*’ to ‘int*’ My intention was that I want to make p volatile. However, once I've read the value of p, I don't care if accessing v is volatile. Why is it required that v be declared volatile? This is hypothetical code of course. In a real situation you could imagine that p points to a memory location, but is modified externally and I want v to point to the location that p pointed to at the time of v = p, even if later p is externally modified. Therefore p is volatile, but v is not. By the way I am interested in the behaviour both when this is considered C and C++, but in C this only generates a warning, not an error.

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  • Creating two Windows by running one as a process from another - C

    - by Jamie Keeling
    Hello, I have a windows form that has a simple menu and performs a simple operation, I want to be able to create another windows form with all the functionality of a menu bar, message pump etc.. as a seperate process so I can then share the results of the operation to the second window. I.E. 1) Form A opens Form B opens as a separate process 2)Form A performs operation 3)Form A passes results via memory to Form B 4)Form B display results I'm confused as to how to go about it, the main app runs fine but i'm not sure how to add a second window if the first one already exists. I hope it makes sense. Thanks!

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  • C++ initializing constants and inheritance

    - by pingvinus
    I want to initialize constant in child-class, instead of base class. And use it to get rid of dynamic memory allocation (I know array sizes already, and there will be a few child-classes with different constants). So I try: class A { public: const int x; A() : x(0) {} A(int x) : x(x) {} void f() { double y[this->x]; } }; class B : A { B() : A(2) {} }; Pretty simple, but compiler says: error C2057: expected constant expression How can I say to compiler, that it is really a constant?

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  • [FreeBSD kernel ]How to maintain a linked list on kernel lever?

    - by Andy Leman
    The situation is: I will implement sets of new system calls. Each of them need to access (read or write) a linked list. So, that means I will have several C programs. So, how can I maintain a linked list in memory and let several programs access it? Or,this is wrong....I should save it as a file? (but I hardly think this is a good idea).. A lot of confused questions here...Need help. Thank you indeed!

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  • C Programming: calling free() on error?

    - by kouei
    Hi all, This a follow up on my previous question. link here. My question is: Let's say I have the following code.. char* buf = (char*) malloc(1024); ... for(; i<20; i++) { if(read(fd, buf, 1024) == -1) { // read off a file and store in buffer perror("read failed"); return 1; } ... } free(buf); what i'm trying to get at is that - what if an error occurs at read()? does that mean my allocated memory never gets freed? If that's the case, how do I handle this? Should I be calling free() as part of error handling? Once again, I apologize for the bad English. ^^; Many thanks, K.

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  • WPF: How to efficiently update an Image 30 times per second

    - by John
    Hello, I'm writing a WPF application that uses a component, and this component returns a pointer (IntPtr) to pixels of a bitmap (stride * height). I know in advance that the bitmap is a 24bits rgb, its width and height. Updating the Image control with these bitmaps makes up a video to the user, but I'm not sure what's the most efficient way to do that, most of the time the CPU usage goes to 75%+ and memory changing from 40mb to 500mb and the nI think GC starts to work and then it drops again to 40mm. The app starts to not be responsive. What shoud I do? thanks!

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  • how to generate large image in compact framework

    - by Buthrakaur
    I need to generate large images (A4 image at 200 DPI, PNG format would be fine) in my compact framework application. This is impossible to do in standard way due to memory limitations (such big image will throw OOMException). Is there any library which offers file-backed stream image generation? Or I could generate many smaller stripes of images (each stripe representing a row of the large image) using standard Bitmap approach, but I need to merge them together afterwards - is there any method how to merge many smaller images into one large without having to instantiate large Bitmap instance (which would again cause OOM)?

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  • Inheriting database connection in PHP OOP

    - by vrode
    My abstract class Database is made for database interaction and any child of this class (UserDatabase, ActionDatabase, EventDatabase) inherits its database connection which is defined as static. `abstract class Database { static $connection = mysql_connect( ); } class UserDatabase extends Database { ... public function __construct( ) { $connection ? "connected" : "not connected"; $this-table = "users"; mysql_query( "FROM " . $this-table . " SELECT *" ); } } ` Does that mean, that my database connection is only set up and stored in memory once and passed on to subclasses as reference without being replicated for each instance? Is this how you would implement you OOP-correct database interface?

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  • android java.lang.OutOfMemoryError

    - by xiangdream
    hi, all, when i download large data from website, i got this error information: I/global (20094): Default buffer size used in BufferedInputStream constructor. It would be better to be explicit if an 8k buffer is required. D/dalvikvm(20094): GC freed 6153 objects / 3650840 bytes in 335ms I/dalvikvm-heap(20094): Forcing collection of SoftReferences for 3599051-byte al location D/dalvikvm(20094): GC freed 320 objects / 11400 bytes in 144ms E/dalvikvm-heap(20094): Out of memory on a 3599051-byte allocation. I/dalvikvm(20094): "Thread-9" prio=5 tid=17 RUNNABLE I/dalvikvm(20094): | group="main" sCount=0 dsCount=0 s=0 obj=0x439b9480 I/dalvikvm(20094): | sysTid=25762 nice=0 sched=0/0 handle=4065496 anyone can help me?

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  • How do I write Push and Pop in Scheme?

    - by kunjaan
    Right now I have (define (push x a-list) (set! a-list (cons a-list x))) (define (pop a-list) (let ((result (first a-list))) (set! a-list (rest a-list)) result)) But I get this result: Welcome to DrScheme, version 4.2 [3m]. Language: Module; memory limit: 256 megabytes. > (define my-list (list 1 2 3)) > (push 4 my-list) > my-list (1 2 3) > (pop my-list) 1 > my-list (1 2 3) What am I doing wrong? Is there a better way to write push so that the element is added at the end and pop so that the element gets deleted from the first?

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  • C++ program runs slow in VS2008

    - by Nima
    I have a program written in C++, that opens a binary file(test.bin), reads it object by object, and puts each object into a new file (it opens the new file, writes into it(append), and closes it). I use fopen/fclose, fread and fwrite. test.bin contains 20,000 objects. This program runs under linux with g++ in 1 sec but in VS2008 in debug/release mode in 1min! There are reasons why I don't do them in batches or don't keep them in memory or any other kind of optimizations. I just wonder why it is that much slow under windows. Thanks,

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  • Which external DSLs do you like to use?

    - by Max Toro
    The reason I'm asking is because right now there seems to be tendency to make DSLs internal. One example is LINQ in C# and VB. You can use it against in-memory objects, or you can use it as a replacement of SQL or other external DSL. Another example is HTML5 vs XHTML2. XHTML2 supported decentralized extensibility through namespaces, in other words you embed external DSL code (XForms, SVG, MathML, etc.) in your XHTML code. Sadly HTML5 doesn't seem to have such mechanism, instead new features are internal (e.g. <canvas> instead of SVG). I'd like to know what other developers think about this. Do you like using external DSLs ? Which ones ? If not, why ?

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  • Does a static object within a function introduce a potential race condition?

    - by Jeremy Friesner
    I'm curious about the following code: class MyClass { public: MyClass() : _myArray(new int[1024]) {} ~MyClass() {delete [] _myArray;} private: int * _myArray; }; // This function may be called by different threads in an unsynchronized manner void MyFunction() { static const MyClass _myClassObject; [...] } Is there a possible race condition in the above code? Specifically, is the compiler likely to generate code equivalent to the following, "behind the scenes"? void MyFunction() { static bool _myClassObjectInitialized = false; if (_myClassObjectInitialized == false) { _myClassObjectInitialized = true; _myClassObject.MyClass(); // call constructor to set up object } [...] } ... in which case, if two threads were to call MyFunction() nearly-simultaneously, then _myArray might get allocated twice, causing a memory leak? Or is this handled correctly somehow?

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  • How do I choose a database?

    - by liamzebedee
    I need a comparison table of some sort for database varieties (MySQL, SQLite etc.). I can't find one. My use case is, I am implementing storage of objects in a distributed hash table. I need a database solution that is: Fast for sorting Simplistic (no users, preferably no additional structures like multiple tables etc.) Concurrent (if possible) Multi-platform File based (not stored in memory primarily) Centralized I will be programming in Go. As I understand, I believe I need what is called a Document Orientated Database, because I am storing objects, identified by keys. EDIT: While I am implementing a DHT, I will also be storing metadata about the objects, such as access counts etc. It would also be preferable to have TLL (time to live)

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  • Double indirection and structures passed into a function

    - by ZPS
    I am curious why this code works: typedef struct test_struct { int id; } test_struct; void test_func(test_struct ** my_struct) { test_struct my_test_struct; my_test_struct.id=267; *my_struct = &my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); } This works, but pointing to the memory address of a functions local variable is a big no-no, right? But if i used a structure pointer and malloc, that would be the correct way, right? void test_func(test_struct ** my_struct) { test_struct *my_test_struct; my_test_struct = malloc(sizeof(test_struct)); my_test_struct->id=267; *my_struct = my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); }

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  • Homemade fstat to get file size, always return 0 length.

    - by Fred
    Hello, I am trying to use my own function to get the file size from a file. I'll use this to allocate memory for a data structure to hold the information on the file. The file size function looks like this: long fileSize(FILE *fp){ long start; fflush(fp); rewind(fp); start = ftell(fp); return (fseek(fp, 0L, SEEK_END) - start); } Any ideas what I'm doing wrong here?

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  • Is it possible to find out what FlashBuilder is doing during compilation?

    - by justkevin
    I've found that Flash Builder 4 (formerly Flex Builder) has trouble working with large projects. After a certain point, builds seem to take longer and longer. I've tried many different ways of improving build time including: Moving embedded resources into externally linked projects. Using -incremental. Tweaking the .ini jvm settings including memory and -server. Turning off automatic build (I'd prefer not to have to do this, because one of the main reasons for using an IDE is to be told about errors as you make them). Deleting the project and re-checking out from the repository. While some of these may help a bit, the performance is still annoyingly slow. I feel if I knew what was taking so long I could refactor my projects to build faster. Is there some setting that tells FlashBuilder to let me see what parts of the build process take so much time?

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  • Could someone give me their two cents on this optimization strategy

    - by jimstandard
    Background: I am writing a matching script in python that will match records of a transaction in one database to names of customers in another database. The complexity is that names are not unique and can be represented multiple different ways from transaction to transaction. Rather than doing multiple queries on the database (which is pretty slow) would it be faster to get all of the records where the last name (which in this case we will say never changes) is "Smith" and then have all of those records loaded into memory as you go though each looking for matches for a specific "John Smith" using various data points. Would this be faster, is it feasible in python, and if so does anyone have any recommendations for how to do it?

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  • Bitmap size exceeds VM budget after second load

    - by jonny
    This is driving me crazy. I have a game which has a bitmap as the background, this is big so I scale it down and this works fine. However when I navigate to another activity and then reload the game screen it crashes on drawing the background. I am calling recycle on all the bitmaps and setting them to null on onDestroy() but this doesn't help. Any ideas and if not how can I debug the memory to see at which step its growing. I looked at getting the heap but nothing of any size is on there really. Thanks.

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  • POST data disapearing on large file upload

    - by DfKimera
    I'm having issues with a file uploading utility in my PHP application. When sending large files (9MB+) over the form, I get a very odd behaviour: the POST data I've included in the form dissapears, including the file information. I've already increased all PHP limits I could (time limit, max input time, post max size, memory limit and upload max filesize) and I still can't get the proper behaviour. I've tried replacing the regular HTTP forms with a Flash-based solution (SWFUpload, www.swfupload.org), still the same behaviour. I've tried multiple files of similar sizes and its definitely not a particular file issue. I've debugged the POST vars sent using Firebug, and the correct variables are still there in the header, together with the file. What could be going on here?

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  • Howto check if a object is connected to another in hibernate

    - by codevourer
    Imagine two domain object classes, A and B. A has a bidirectional one-to-many relationship to B. A is related to thousands of B. The relations must be unique, it's not possible to have a duplicate. To check if an instance of B is already connected to a given instance of A, we could perform an easy INNER JOIN but this will only ensure the already persisted relations. What about the current transient relations? class A { @OneToMany private List<B> listOfB; } If we access the listOfB and perform a check of contains() this will fetch all the connected instances of B lazy from the datasource. I only want to validate them by their primary-key. Is there an easy solution where I can do things like "Does this instance of A is connected with this instance of B?" Without loading all these data into memory and perform a based on collections?

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  • Java Web App: Passing form parameters across multiple pages

    - by digiarnie
    Hi, what is the best practice or best way of passing form parameters from page to page in a flow? If I have a flow where a user enters data in a form and hits next and repeats this process until they get to an approval page, what ways could I approach this problem to make the retention of data as simple as possible over the flow? I guess you could put all the information as you go in the session but could you get into memory issues if a lot of people are using your app and going through the flow at the same time?

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  • Predicting performance for an iPhone/iPod Touch App

    - by Avizz
    I don't have an iPhone Developer Program Account yet and will be getting one in the next couple of days. Can instruments be used with the simulator to give a rough estimate on how well my app may perform? Using instruments I checked and fixed all the leaks it was detecting, and it appears that my memory usage maxes out at about 5.77mb. Is there any other tests I could perform with instruments to judge how well my app would perform? I realize there is no way other then the actual device to get a definite answer, it would be nice to get an estimate.

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  • c, pass awk syntax as argument to execl

    - by Skuja
    I want to run following command in c to read systems cpu and memory usage: ps aux|awk 'NR > 0 { cpu +=$3; ram+=$4 }; END {print cpu,ram}' I am trying to pass it to execl command and after that read its output: execl("/bin/ps", "/bin/ps", "aux|awk", "'NR > 0 { cpu +=$3; ram+=$4 }; END {print cpu,ram}'",(char *) 0); but in terminal i am getting following error: ERROR: Unsupported option (BSD syntax) I would like to know how to properly pass awk as argument to execl?

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