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• Performance of Serialized Objects in C++

  - by jm1234567890

  Hi Everyone, I'm wondering if there is a fast way to dump an STL set to disk and then read it back later. The internal structure of a set is a binary tree, so if I serialize it naively, when I read it back the program will have to go though the process of inserting each element again. I think this is slow even if it is read back in correct order, correct me if I am wrong. Is there a way to "dump" the memory containing the set into disk and then read it back later? That is, keep everything in binary format, thus avoiding the re-insertion. Do the boost serialization tools do this? Thanks! EDIT: oh I should probably read, http://www.parashift.com/c++-faq-lite/serialization.html I will read it now... no it doesn't really help

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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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• Small questions on data structure

  - by John Graveston

  Hi, I'm trying to search the parent of a node with Kruskal's algorithm. My program works just fine, but I think I have heard of a method to improve the speed of the algorithm by reconstructing the tree while searching for the parent node and connecting it to the parent node. I'm pretty sure that I've heard of this somewhere, maybe in a lecture. Can anyone refresh my memory? And also, given a number of arrays, when searching for the minimum and the maximum value from a certain section of an array, what is the name of the tree that can calculate the minimum/maximum value from the array by making a binary tree that has the minimum/maximum value of each array in O(log N)?

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• Express one dimension of 2d array as new array

  - by user208080

  I have a 2d array a[3,3]. How can I express one dimension as a new array and pass it to some function? 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 Also, can I create a 65000x65000 array with C#? I got some "out of memory" error.

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• Declaration and initialization of local variables - what is most C++ like?

  - by tuergeist

  Hi, I did not find any suitable questions answered yet, so I'd like to know what is "better" C++ style in the mean of performance and/or memory. Both codes are inside a method. The question is: When to declare long prio? And what are the implications? Code 1 while (!myfile.eof()) { getline(myfile, line); long prio = strtol(line); // prio is declared here // put prio in map... // some other things } Code 2 long prio; // prio is declared here while (!myfile.eof()) { getline(myfile, line); prio = strtol(line); // put prio in map... // some other things }

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• is there a flag "M_FAST" in FreeBSD kernel for Malloc Call ?

  - by KaluSingh Gabbar

  if you know there is one, can you let me know what its for ? if not please say so : ) thanks. Signature : void * malloc(unsigned long size, struct malloc_type type, int flags); for example. other flags are... M_ZERO Causes the allocated memory to be set to all zeros. M_WAITOK Indicates that it is OK to wait for resources. If the request cannot be immediately fulfilled, the current process is put to sleep to wait for resources to be released by other processes. The malloc(), realloc(), and reallocf() functions cannot return NULL if M_WAITOK is specified.** This is the root of my confusion EDIT: The clarification for M_FAST is made in my answer below.

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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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• Object for storing strings in Python

  - by evg

  class MyWriter: def __init__(self, stdout): self.stdout = stdout self.dumps = [] def write(self, text): self.stdout.write(smart_unicode(text).encode('cp1251')) self.dumps.append(text) def close(self): self.stdout.close() writer = MyWriter(sys.stdout) save = sys.stdout sys.stdout = writer I use self.dumps list to store data obtained from prints. Is there a more convenient object for storing string lines in memory? Ideally I want dump it to one big string. I can get it like this "\n".join(self.dumps) from code above. May be it's better to just concatenate strings - self.dumps += text?

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• problem using keil uvision 3

  - by Blossom

  I am trying to compile a C code using Keil uvision 3. The entire code gets compiled only if I use large memory model by choosing option xdata for target. To use this model I have to use external data RAM which is not possible for me due to some reasons. So I decided to go with pdata option. Can anybody please help me with the exact steps to be carried out for using pdata? I am using 89V51RD2. I am much confused with the options like BL51 MISC, BL51 Locate etc.

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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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• INSERT INTO ... SELECT ... vs dumping/loading a file in MySQL

  - by Daniel Huckstep

  What are the implications of using a INSERT INTO foo ... SELECT FROM bar JOIN baz ... style insert statement versus using the same SELECT statement to dump (bar, baz) to a file, and then insert into foo by loading the file? In my messing around, I haven't seen a huge difference. I would assume the former would use more memory, but the machine that this runs on has 8GB of RAM, and I never even see it go past half used. Are there any huge (or long term) performance implications that I'm not seeing? Advantages/disadvantages of either?

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• MySQL: Query to obtain recipes using all given ingredients.

  - by John_A

  hi I have the following simplified tables: CREATE TABLE recipe(id int, name varchar(25)); CREATE TABLE ingredient(name varchar(25)); CREATE TABLE uses_ingredient(recipe_id int, name varchar(25)); I want to make a query that returns all id's of recipes that contain both Chicken and Cream. I have tried SELECT recipe_id FROM uses_ingredient INNER JOIN (SELECT * FROM ingredient WHERE name="Chicken" OR name="Cream") USING (name) GROUP BY recipe_id HAVING COUNT(recipe_id) >= (SELECT COUNT(*) FROM theme); which gives me :"ERROR 1248 (42000): Every derived table must have its own alias" and is probably wrong too. Next I tried SELECT recipe_id FROM (SELECT * FROM ingredient WHERE name="Chicken" OR name="Cream") AS t INNER JOIN uses_ingredient USING (name) GROUP BY recipe_id HAVING COUNT(recipe_id)>= (SELECT COUNT(*) FROM t); which gives "ERROR 1146 (42S02): Table 'recipedb.t' doesn't exist" I want to avoid creating temporary tables including using ENGINE=MEMORY.

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• I want to make my own Malloc

  - by Unknown

  I want to make my own malloc/free so I can make a precise copying allocator. Any gurus have any tips and suggestions? I have a few questions for now: Should I just malloc large chunks of memory, and then distribute from that so I don't have to call the system calls? How are copying collectors usually done? I would imagine that this part is a bit complicated to do efficiently. My naive implementation would just malloc a block the size of the remaining objects which would require 2x the space.

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• Comparing large strings in JavaScript with a hash

  - by user4815162342

  I have a form with a textarea that can contain large amounts of content (say, articles for a blog) edited using one of a number of third party rich text editors. I'm trying to implement something like an autosave feature, which should submit the content through ajax if it's changed. However, I have to work around the fact that some of the editors I have as options don't support an "isdirty" flag, or an "onchange" event which I can use to see if the content has changed since the last save. So, as a workaround, what I'd like to do is keep a copy of the content in a variable (let's call it lastSaveContent), as of the last save, and compare it with the current text when the "autosave" function fires (on a timer) to see if it's different. However, I'm worried about how much memory that could take up with very large documents. Would it be more efficient to store some sort of hash in the lastSaveContent variable, instead of the entire string, and then compare the hash values? If so, can you recommend a good javascript library/jquery plugin that implements an appropriate hash for this requirement?

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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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• GCC compiler -- bug or unspecified behavior?

  - by Jared P

  When I have conflicting definitions of the ivars of a class in objective-c (not redeclaring the class in the same file, but rather naming the same class with diff ivars, no warnings or better yet errors are issued by the compiler. However, both sets of ivars are useable by the appropriate methods in the respective files. For instance Foo.m: @interface foo { int a; } - (int)method; @end @implementation foo - (int)method { return a; } @end Bar.m: @interface foo { float baz; } @end @implementation foo (category) - (float)blah { return baz; } @end compiles without warnings or errors. Is this intentional? Is this an unchecked error? (for the record, a and baz are actually the same memory location.)

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• C++ vector reference parameter

  - by Archanimus

  Hello folks, let's say we have a class class MyClass { vector<vector<int > > myMatrice; public : MyClass(vector<vector<int > > &); } MyClass::MyClass(vector<vector<int > > & m) { myMatrice = m; } During the instanciation of MyClass, I pass a big vector < vector < int and I find that the object is actually copied and not only the reference, so it takes the double of the memory ... Please, can anyone help me out with this problem, I'm stuck since too many time ... And thanks a lot!

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• Mootools event leak

  - by user572263

  The example to demonstrate the issue can be found here: link text The test shows a basic Mootools class that contains an element variable with a click event attached. There’s also a “cleanup” function to remove the event and nullify the element variable. My problem is that when I loop a thousand times to create the “LeakClass” instance and clean it up, it causes a major memory leak like there’s no tomorrow. I tested this on IE8 and Chrome. On the other hand what I’ve noticed is that if I comment out the line that adds the “click” event, the code doesn’t leak. Can somebody please help me structure the class/event in a manner that it doesn’t leak. Thanks in advance.

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• Flipping an image using a one dimensional array of characters.

  - by Jeff

  I have the data of an image loaded into memory as a one dimensional array. Since I'm trying to use OpenGL to draw it, and since it reads from the bottom up, I want to try and flip the elements of the array before they're sent to OpenGL. Maybe there's a way to tell OpenGL to read from the top to the bottom? Anyways, I tried using a few methods of sorting arrays and they also flip the image horizontally, which is very much like the original problem. So can I flip the data only one way?

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• Zend_Soap with attachments (server)

  - by Tom

  i'm trying to build a SOAP service with Zend_Soap. Everything is working great but the client needs the ability to send attachments to the service (not base64 encoded strings, as this service will be called multiple times a day with various file sizes so processing all that in memory is not possible. So I'd like to handle a normal SOAP attachment (DIME/MIME) with the SOAP server in Zend Framework however I'm unable to find documentation about it. Can I access it with $_FILES[] or any other way? Is it even possible in Zend_Soap (as there's not that much info available). SOAP is a must - so thanks for the advice but it has to be SOAP, not REST.

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• How should I store this 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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• pointers for getting elements of an array in C

  - by Manolo

  I am a newbie in C and I would like to get the elements of an array with a function, I have tried different options, but I still do not get the elements. My function is: void getelements(int *a, int cl) { int *p; for (p=&a[0];p<&a[cl];p++) { printf("%d\n",*p); } } I know that the solution should work like that, but it only prints the first element and then memory positions. I am calling my function with: int v={10,12,20,34,45}; getelements(&v,5); Any help? I need to use arithmetic of pointers. Thanks

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• C# thread safety for class instances

  - by Steveng

  I am learning C# and I am confused with the thread safety of the copies of the class instances as below: eg: classA objA; classA objB = objA; objA.field1 = value2; //do I need lock around modification of field1? //let say we pass the objB to another thread objB.field1 = value1 //do I need a lock for objB because of the modification of field1? I am confused because coming from the background of C++, the class in C# is the reference type. If both objA and objB refer to the same memory underlying, then I would need a lock to protect the simultaneous writing to the field1. Could someone confirm with this or am I missing something? Thanks.

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• a macro question for c language (#define)

  - by Daniel

  I am reading source code of hoard memory allocator, and in the file of gnuwrapper.cpp, there are the following code #define CUSTOM_MALLOC(x) CUSTOM_PREFIX(malloc)(x) What's the meaning of CUSTOM_PREFIX(malloc)(x)? is CUSTOM_PREFIX a function? But as a function it didn't defined anywhere. If it's variable, then how can we use variable like var(malloc)(x)? more code: #ifndef __GNUC__ #error "This file requires the GNU compiler." #endif #include <string.h> #include <stdlib.h> #include <stdio.h> #include <malloc.h> #ifndef CUSTOM_PREFIX ==> here looks like it's a variable, so if it doesn't define, then define here. #define CUSTOM_PREFIX #endif #define CUSTOM_MALLOC(x) CUSTOM_PREFIX(malloc)(x) ===> what's the meaning of this? #define CUSTOM_FREE(x) CUSTOM_PREFIX(free)(x) #define CUSTOM_REALLOC(x,y) CUSTOM_PREFIX(realloc)(x,y) #define CUSTOM_MEMALIGN(x,y) CUSTOM_PREFIX(memalign)(x,y)

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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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