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• Rationale in selecting Hash Key type

  - by Amrish

  Guys, I have a data structure which has 25 distinct keys (integer) and a value. I have a list of these objects (say 50000) and I intend to use a hash table to store/retrieve them. I am planning to take one of these approaches. Create a integer hash from these 25 integer keys and store it on a hash table. (Yeah! I have some means to handle collisions) Make a string concatenation on the individual keys and use it as a hash key for the hash table. For example, if the key values are 1,2,4,6,7 then the hash key would be "12467". Assuming that I have a total of 50000 records each with 25 distinct keys and a value, then will my second approach be a overkill when it comes to the cost of string comparisons it needs to do to retrieve and insert a record? Some more information! Each bucket in the hash table is a balanced binary tree. I am using the boost library's hash_combine method to create the hash from the 25 keys.

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• C++ MACRO that will execute a block of code and a certain command after that block.

  - by Poni

  void main() { int xyz = 123; // original value { // code block starts xyz++; if(xyz < 1000) xyz = 1; } // code block ends int original_value = xyz; // should be 123 } void main() { int xyz = 123; // original value MACRO_NAME(xyz = 123) // the macro takes the code code that should be executed at the end of the block. { // code block starts xyz++; if(xyz < 1000) xyz = 1; } // code block ends << how to make the macro execute the "xyz = 123" statement? int original_value = xyz; // should be 123 } Only the first main() works. I think the comments explain the issue. It doesn't need to be a macro but to me it just sounds like a classical "macro-needed" case. By the way, there's the BOOST_FOREACH macro/library and I think it does the exact same thing I'm trying to achieve but it's too complex for me to find the essence of what I need. From its introductory manual page, an example: #include <string> #include <iostream> #include <boost/foreach.hpp> int main() { std::string hello( "Hello, world!" ); BOOST_FOREACH( char ch, hello ) { std::cout << ch; } return 0; }

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• Assign weight to a integer column for Sphinx search

  - by Daniel

  Hello: I have a note table with columns: title :string content :text rating :integer and a thinking_sphinx configuration: define_index do indexes :title, :sortable => true indexes :content end Then I can search the notes and assign weights to title and content to define the order or the result: Note.search "abc", :match_mode => :extended, :field_weights => { :title => 10, :content => 3 } Now I want to assign a weight to the rating column The type of the rating column is integer. The range of the rating is [1, 2, 3, 4, 5]. Can I just add weight at the :field_weights :field_weights => { :title => 10, :content => 3, :rating => 5 } or I need to do something else to make the note which has higer rating display first?

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• iOS Development: Why isn't my try block catching the exception?

  - by BeachRunnerJoe

  Hi. I have an exception being thrown in my code, but when I wrap it in an try/catch block, it doesn't get caught. The NSLog statement is never called in the catch block. Here's the code... NSInteger quoteLength; [data getBytes:(void *)&quoteLength range:NSMakeRange(sizeof(messageType), sizeof(quoteLength))]; @try { //Debugger stack trace shows an NSException being thrown on this statement NSData *stringData = [data subdataWithRange:NSMakeRange(sizeof(messageType) + sizeof(quoteLength), [data length])]; NSString *quote = [[NSString alloc] initWithData:stringData encoding:NSUTF8StringEncoding]; NSLog(@"received quote: %@",quote); [quote release]; } @catch (NSException * e) { NSLog(@"Exception Raised: %@", [e reason]); } Why doesn't it get caught? Thanks so much!

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• C++ compilers and back/front ends

  - by aaa

  Hello. for my own education I am curious what compilers use which C++ front-end and backend. Can you enlighten me where the following technologies are used and what hallmarks/advantages they have if any? Open64 - is it backend, front-end, or both? Which compilers use it? I encounter it in cuda compiler. EDG - as far as I can tell this is a backend use by Intel compilers and Comeau. do other compilers use it? I found quite a few references to it in boost source code. ANTLR - this is general parser. Do any common compilers use it? Regarding compilers: with front-end/backend does gcc compiler suite uses? does it have common heritage with any other compiler? what front-end/backend PGI and PathScale compilers use? what front-end/backend XL compiler uses (IBM offering). Thanks.

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• c++ Initializing a struct with an array as a member

  - by Drew Shafer

  I've got the following reduced testcase: typedef struct TestStruct { int length; int values[]; }; TestStruct t = {3, {0, 1, 2}}; This works with Visual C++, but doesn't compile with g++ under linux. Can anyone help me make this specific kind of initializer portable? Additional details: the actual structure I'm working with has several other int values, and the array can range in length from a single entry to over 1800 entries. Any help much appreciated. Thanks!

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• T-SQL Operations on a Calculated Date Field

  - by firedrawndagger

  Can I do WHERE operations on a calculated date field? I have a lookup field, which has been written badly in SQL and unfortunately I can't change it. But basically it stores dates as characters such as "July-2010" or "June-2009" (along with other non date data). I want to extract the dates first (which I did using a LIKE opertor) and then extract data based on a date range. SELECT BusinessUnit, Lookup, ReleaseDate FROM ( SELECT TOP 10 LookupColumn As Lookup, BU as BusinessUnit, CONVERT(DATETIME, REPLACE(LookupColumn,'-',' ')) as ReleaseDate FROM [dbo].[LookupTable] WHERE LookupColumn LIKE N'%-2010' ) MyTable ORDER BY ReleaseDate WHERE ReleaseDate = '2010-02-01' I'm having issues with WHERE operator. I would assume creating a subquery to encapsulate the calculated field would allow me to do operations with it such as WHERE but maybe I'm wrong. Bottom line is it possible to do operations on calculated fields?

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• Format Text Field While User Enters Data

  - by Matt

  Hello, so here is what I am trying to do. I have a birth date text field, while the user in puts text i want the field to automatically put it in the form YYYY-MM-DD. Basically while the user types it replaces the Y's M's and D's but leaves the hyphen. I am not sure how to go about this i may need a mask or something. I know this is where some of the formatting can be done - (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string{ Any help would be of much help

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• Online Game programming in Google App Engine: AI

  - by Hortinstein

  I am currently in the planning stages of a game for google app engine, but cannot wrap my head around how I am going to handle AI. I intend to have persistant NPCs that will move about the map, but short of writing a program that generates the same XML requests I use to control player actions, than run it on another server I am stuck on how to do it. I have looked at the Task Queue feature, but due to long running processes not being an option on the App engine, I am a little stuck. I intend to run multiple server instances with 200+ persistant NPC entities that I will need to update. Most action is slowly roaming around based on player movements/concentrations, and attacking close range players(you can probably guess the type of game im developing)

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• Unwanted behaviour from dict.fromkeys

  - by Anthony Labarre

  Hi there, I'd like to initialise a dictionary of sets (in Python 2.6) using dict.fromkeys, but the resulting structure behaves strangely. More specifically: >>>> x = {}.fromkeys(range(10), set([])) >>>> x {0: set([]), 1: set([]), 2: set([]), 3: set([]), 4: set([]), 5: set([]), 6: set([]), 7: set([]), 8: set([]), 9: set([])} >>>> x[5].add(3) >>>> x {0: set([3]), 1: set([3]), 2: set([3]), 3: set([3]), 4: set([3]), 5: set([3]), 6: set([3]), 7: set([3]), 8: set([3]), 9: set([3])} I obviously don't want to add 3 to all sets, only to the set that corresponds to x[5]. Of course, I can avoid the problem by initialising x without fromkeys, but I'd like to understand what I'm missing here.

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• Creating serializeable unique compile-time identifiers for arbitrary UDT's.

  - by Endiannes

  I would like a generic way to create unique compile-time identifiers for any C++ user defined types. for example: unique_id<my_type>::value == 0 // true unique_id<other_type>::value == 1 // true I've managed to implement something like this using preprocessor meta programming, the problem is, serialization is not consistent. For instance if the class template unique_id is instantiated with other_type first, then any serialization in previous revisions of my program will be invalidated. I've searched for solutions to this problem, and found several ways to implement this with non-consistent serialization if the unique values are compile-time constants. If RTTI or similar methods, like boost::sp_typeinfo are used, then the unique values are obviously not compile-time constants and extra overhead is present. An ad-hoc solution to this problem would be, instantiating all of the unique_id's in a separate header in the correct order, but this causes additional maintenance and boilerplate code, which is not different than using an enum unique_id{my_type, other_type};. A good solution to this problem would be using user-defined literals, unfortunately, as far as I know, no compiler supports them at this moment. The syntax would be 'my_type'_id; 'other_type'_id; with udl's. I'm hoping somebody knows a trick that allows implementing serialize-able unique identifiers in C++ with the current standard (C++03/C++0x), I would be happy if it works with the latest stable MSVC and GNU-G++ compilers, although I expect if there is a solution, it's not portable.

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• What wrapper class in C++ should I use for automated resource management?

  - by Vilx-

  I'm a C++ amateur. I'm writing some Win32 API code and there are handles and weirdly compositely allocated objects aplenty. So I was wondering - is there some wrapper class that would make resource management easier? For example, when I want to load some data I open a file with CreateFile() and get a HANDLE. When I'm done with it, I should call CloseHandle() on it. But for any reasonably complex loading function there will be dozens of possible exit points, not to mention exceptions. So it would be great if I could wrap the handle in some kind of wrapper class which would automatically call CloseHandle() once execution left the scope. Even better - it could do some reference counting so I can pass it around in and out of other functions, and it would release the resource only when the last reference left scope. The concept is simple - but is there something like that in the standard library? I'm using Visual Studio 2008, by the way, and I don't want to attach a 3rd party framework like Boost or something.

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• C++ ambiguous template instantiation

  - by aaa

  the following gives me ambiguous template instantiation with nvcc (combination of EDG front-end and g++). Is it really ambiguous, or is compiler wrong? I also post workaround à la boost::enable_if template<typename T> struct disable_if_serial { typedef void type; }; template<> struct disable_if_serial<serial_tag> { }; template<int M, int N, typename T> __device__ //static typename disable_if_serial<T>::type void add_evaluate_polynomial1(double *R, const double (&C)[M][N], double x, const T &thread) { // ... } template<size_t M, size_t N> __device__ static void add_evaluate_polynomial1(double *R, const double (&C)[M][N], double x, const serial_tag&) { for (size_t i = 0; i < M; ++i) add_evaluate_polynomial1(R, C, x, i); } // ambiguous template instantiation here. add_evaluate_polynomial1(R, C, x, serial_tag());

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• C# filter results quarterly

  - by user339067

  Hello! I am writing a simple C# application that is handling bank savings. I want to be able to show the results on either, yearly, monthly or quarterly basic how can this be done? How can I loop through a set of results and only show every third post (if I am using quarterly) for example. In Python I can use range(1,31,3) but how is it done in C#? UPDATE 1 I want to loop 12 times (annually) and calculate the interest each loop but I only want to print the results every third loop (quarterly). How can I achieve this? Please help!

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• Circumvent c++ null-terminated string frustration

  - by ypnos

  I'm using boost::program_options and it suffers from the same as many other c++ libs, even std itself: It still uses C-style null-terminated strings, because nobody really likes the weak std::string. The method in question is: options_description_easy_init& operator()(const char* name, const value_semantic* s, const char* description); The typical use case is just fine: options.add_options() ("graphical", bool_switch(&isGraphical)->default_value(false), "Show any graphical output during runtime") However, I need the name of the option to be set dynamically. The reason is that in some cases I nead a custom prefix, which is added to the string by my function std::string key(const std::string& k): options.add_options() (key("graphical"), bool_switch(&isGraphical)->default_value(false), "Show any graphical output during runtime") This fails. I could now use c_str() on the std::string but that's evil -- I don't know how long program_options keeps the variable around and if my string is still alive when needed. I could also reserve memory in a buffer etc. and hand in that. The buffer is never freed and it sucks/is evil. Is there anything else I can do to circumvent the C-style string mess in this situation?

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• What alternatives are there to Google App Engine?

  - by Chris Marasti-Georg

  What alternatives are there to GAE, given that I already have a good bit of code working that I would like to keep. In other words, I'm digging python. However, my use case is more of a low number of requests, higher CPU usage type use case, and I'm worried that I may not be able to stay with App Engine forever. I have heard a lot of people talking about Amazon Web Services and other sorts of cloud providers, but I am having a hard time seeing where most of these other offerings provide the range of services (data querying, user authentication, automatic scaling) that App Engine provides. What are my options here?

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• Microphone input

  - by George

  I'm trying to build a gadget that detects pistol shots using Android. It's a part of a training aid for pistol shooters that tells how the shots are distributed in time and I use a HTC Tattoo for testing. I use the MediaRecorder and its getMaxAmplitude method to get the highest amplitude during the last 1/100 s but it does not work as expected; speech gives me values from getMaxAmplitude in the range from 0 to about 25000 while the pistol shots (or shouting!) only reaches about 15000. With a sampling frequency of 8kHz there should be some samples with considerably high level. Anyone who knows how these things work? Are there filters that are applied before registering the max amplitude. If so, is it hardware or software? Thanks, /George

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• Validate decimal number in (known) national format

  - by Álvaro G. Vicario

  PHP has many built-in functions to validate numbers but they all expect input in computer format: 1234.56. I need to validate stuff like 1,234.56 (English) or 1.234,56 (Spanish), together with some typical attributes (accepted range, max number of decimals, etc.). I started writing my own function but I soon got lost. It's easy to read the user input into a float variable but I want to be able to detect numbers with invalid formats like 1,23456.7 or 1..25. Do you have any recommendation on the subject? (Decimal and thousand characters are known beforehand and it's okay to hard-code digit groups as three, there's no need to cover Indian number format.)

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• C++ Adding 2 arrays together quickly

  - by Tom Gullen

  Hello! Given the arrays: int canvas[10][10]; int addon[10][10]; Where all the values range from 0 - 100, what is the fastest way in C++ to add those two arrays so each cell in canvas equals itself plus the corresponding cell value in addon. IE, I want to achieve something like: canvas += another; So if canvas[0][0] =3 and addon[0][0] = 2 then canvas[0][0] = 5 Speed is essential here as I am writing a very simple program to brute force a knapsack type problem and there will be tens of millions of combinations.

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• Regexp in iOS to find comments

  - by SteveDolphin23

  I am trying to find and process 'java-style' comments within a string in objective-C. I have a few regex snippets which almost work but I am stuck on one hurdle: different options seem to make the different styles work. For example, I am using this to match: NSArray* matches = [[NSRegularExpression regularExpressionWithPattern:expression options:NSRegularExpressionAnchorsMatchLines error:nil] matchesInString:string options:0 range:searchRange]; The options here allow me successfully find and process single line comments (//) but not multiline (/* */), if I change the option to NSRegularExpressionDotMatchesLineSeparators then I can make multiline work fine but I can't find the 'end' of a single line comment. I suppose really I need dot-matches-line-separators but I need a better way of finding the end of a single line comment? The regexp I have so far are: @"/\\*.*?\\*/" @"//.*$" it's clear to see if dot matches a line separator then the second one (single line) never 'finishes' but how do I fix this? I found some suggestions for single line that were more like: @"(\/\/[^"\n\r]*(?:"[^"\n\r]*"[^"\n\r]*)*[\r\n])" But that doesn't' seem to work at all! Thanks in advance for any pointers.

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• c++ specialized overload?

  - by acidzombie24

  -edit- i am trying to close the question. i solved the problem with boost::is_base_and_derived In my class i want to do two things. 1) Copy int, floats and other normal values 2) Copy structs that supply a special copy function (template T copyAs(); } the struct MUST NOT return int's unless i explicitly say ints. I do not want the programmer mistaking the mistake by doing int a = thatClass; -edit- someone mention classes dont return anything, i mean using the operator Type() overload. How do i create my copy operator in such a way i can copy both 1) ints, floats etc and the the struct restricted in the way i mention in 2). i tried doing template <class T2> T operator = (const T2& v); which would cover my ints, floats etc. But how would it differentiate from structs? so i wrote T operator = (const SomeGenericBase& v); The idea was the GenericBase would be unsed instead then i can do v.Whatever. But that backfires bc the functions i want wouldnt exist, unless i use virtual, but virtual templates dont exist. Also i would hate to use virtual I think the solution is to get rid of ints and have it convert to something that can do .as(). So i wrote something up but now i have the same problem, how does that differentiate ints and structs that have the .as() function template?

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• Network Communication program in python

  - by lamnep

  Hi all, Basically what I'm trying to achieve is a program which allow users to connect to a each other over a network in, essentially, a chat room. What I'm currently struggling with is writing the code so that the users can connect to each other without knowing the IP-address of the computer that the other users are using or knowing the IP-address of a server. Does anyone know of a way in which I could simply have all of the users scan the IP range of my network in order to find any active 'room' and then give the user a chance to connect to it? Also, the hope is that there will be no need for a central server to run this from, rather every user will simply be connected to all other user, essentially being the server and client at the same time.

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• Vim: replacing start and end of a visual char, line or block

  - by gattu marrudu

  I am trying to find a shortcut to place a custom comment sequence on my code, e.g.: /* start of comment blah end of comment /**/ (it is easier to void the comment by just adding a / to the beginning) I would like to do this in Vim by selecting a visual line, block or char and adding '/' characters at the beginning of the block and '/*/' at the end, plus newlines. After selecting some lines (Shift-V) I tried this: '<,'>s/\(.*\)/\/*\r\1\r\/**\// But it adds the comment chars at EACH newline. How can I only apply the substitution at the beginning and end of the selected range? Thanks gm

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• Value from UISlider method?

  - by fuzzygoat

  Can anyone point me in the right direction regarding sliders, the version below was my first attempt (the range is 0.0 - 100.0) The results I get are not right. // Version 1.0 -(IBAction)sliderMoved:(id)sender { NSLog(@"SliderValue ... %d",(int)[sender value]); } // OUTPUT: // [1845:207] SliderMoved ... -1.991753 // [1845:207] SliderMoved ... 0.000000 // [1845:207] SliderMoved ... 0.000000 // [1845:207] SliderMoved ... 32768.000435 With the version below I get the values I expect, what am I missing in version_001? // Version 2.0 -(IBAction)sliderMoved:(UISlider *)sender { NSLog(@"SliderValue ... %d",(int)[sender value]); } // OUTPUT: // [1914:207] SliderMoved ... 1 // [1914:207] SliderMoved ... 2 // [1914:207] SliderMoved ... 3 // [1914:207] SliderMoved ... 4 cheers Gary

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• Is it possible to load an entire SQL Server CE database into RAM?

  - by DanM

  I'm using LinqToSql to query a small SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table via a foreign key, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of the appeal of LinqToSql. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view.

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