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• Toubleshooting mapkit performance

  - by brettr

  I'm plotting over 500 points on a map using mapkit. Zooming is a little jittery compared to the native google map app. I've discovered what is causing the slowness. I'm adding custom annotations so that I can later add different pin colors and buttons for detail views: - (MKAnnotationView *) mapView:(MKMapView *)mapView viewForAnnotation:(AddressNote *) annotation { MKPinAnnotationView *annView=[[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"currentlocation"]; annView.pinColor = MKPinAnnotationColorGreen; annView.animatesDrop=TRUE; annView.canShowCallout = YES; annView.calloutOffset = CGPointMake(-5, 5); return annView; } If I comment out the above code, everything works fine. Very smooth with zooming in/out. Should I be adding annotations differently to boost performance?

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• The ctags command doesn't recurse saying "it is not a regular file".

  - by indiv

  When I run ctags -R *, I get errors saying that all directories are not regular files and it skips them instead of recursively generating tags for them. ctags: skipping arpa: it is not a regular file. ctags: skipping asm: it is not a regular file. ctags: skipping asm-generic: it is not a regular file. ctags: skipping bits: it is not a regular file. ctags: skipping blkid: it is not a regular file. ctags: skipping boost: it is not a regular file. What is the problem?

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• Using * in SELECT Query

  - by libregeek

  I am currently porting an application written in MySQL3 and PHP4 to MySQL5 and PHP5. On analysis I found several SQL queries which uses "select * from tablename" even if only one column(field) is processed in PHP. The table has almost 60 columns and it has a primary key. In most cases, the only column used is id which is the primary key. Will there be any performance boost if I use queries in which the column names are explicitly mentioned instead of * ? (In this application there is only one method which we need all the columns and all other methods return only a subset of the columns)

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• If-elseif-else Logic Question

  - by Changeling

  I have a set of three values, call them x, y, and z. If value A happens to match only one in the set x, y, and z, then that means we have a proper match and we stop searching for a match, even if it is at y. It can match any one in that set. These values x, y, and z are non-constant so I cannot use a switch-case statement. How do I do this with an if-elseif-else statements without having to use GOTO. I am using C++ (no boost or any of that other fancy stuff). Now, I am trying to do this in code and it is racking my brain this morning (not enough coffee?)

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• Container of shared_ptr's but iterate with raw pointers

  - by Sean Lynch

  I have a class that holds a list containing boost::shared_ptrs to objects of another class. The class member functions that give access to the elemets in the list return raw pointers. For consistency I'd also like to be able to iterate with raw pointers instead of shared_ptrs. So when I dereference the list iterator, I'd like to get raw pointer, not a shared_ptr. I assume I need to write a custom iterator for this. Is this correct? If so can someone point me in the right direction - I've never done this before.

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• Expression Tree : C#

  - by nettguy

  My understanding of expression tree is : Expression trees are in-memory representation of expression like arithmetic or boolean expression.The expressions are stored into the parsed tree.so we can easily transalate into any other language. Linq to SQL uses expression tree.Normally when our LINQ to SQL query compiler translates it to parsed expression trees.These are passed to Sql Server as T-SQL Statements.The Sql server executes the T-SQL query and sends down the result back.That is why when you execute LINQ to SQL you gets IQueryable<T> not IEnumetrable<T>.Because IQuerybale contains public IQueryable:IEnumerable { Type Element {get;} Expression Expression {get;} IQueryaleProvider Provider {get;} } Questions : Microsoft uses Expression trees to play with LINQ-to-Sql.What are the different ways can i use expression trees to boost my code. Apart from LINQ to SQL,Linq to amazon ,who used expression trees in their applications? Linq to Object return IEnumerable,Linq to SQL return IQueryable ,What does LINQ to XML return?

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• Easy way to parse a url in C++ cross platform?

  - by Andrew Bucknell

  I need to parse a url to get the protocol host path and query in an application I am writing in c++. The application is intended to be cross platform. Im surprised I cant find anything that does this in boost or poco libraries. Is it somewhere obvious Im not looking? Any suggestions on appropriate open source libs? Or is this something I just have to do my self? Its not super complicated but it seems such a common task I am surprised there isnt a common solution.

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• Is there a standard Cyclic Iterator in C++

  - by Hippicoder

  Based on the following question: Check if one string is a rotation of other string I was thinking of making a cyclic iterator type that takes a range, and would be able to solve the above problem like so: std::string s1 = "abc" ; std::string s2 = "bca" ; std::size_t n = 2; // number of cycles cyclic_iterator it(s2.begin(),s2.end(),n); cyclic_iterator end; if (std::search(it, end, s1.begin(),s1.end()) != end) { std::cout << "s1 is a rotation of s2" << std::endl; } My question, Is there already something like this available? I've check Boost and STL doesn't have one. I've got a simple hand-written one but would rather use an already made/tested implementation.

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• Slow Speeds when unzipping with PHP onto a NFS, how can I speed it up?

  - by bunwich

  Hi, I'm trying to figure out how to boost my NFS speed and php uploads. File is uploaded to the webserver's local tmp dir With PHP I copy the file userxxx.zip to the NFS With PHP I extract the userxxx.zip on the NFS to another dir on the NFS. What I'm finding is the file is in Step 3, the file is being read through the NFS by the web server, processed by the web server, and uploaded back across the NFS. Speeds as expected are very slow. Might a possible solution be to get the Fileserver to extract the zip? a) Webserver copies the file to the NFS b) Webserver makes a web service call to the Fileserver c) Fileserver can now unzip the file like it's local and the speeds should be much faster. I would appreciate any suggestion anyone how people have approached this problem. (I'm aware that php ZipArchive() is very slow, and I'll likely use java or php exec unzip to speed it up) Thanks

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• Database caching on a shared host

  - by tau

  Anyone have any ideas how to increase MySQL performance on a shared host? My question has less to do with overall database performance and more to do with simply retrieving user-submitted data. Currently my database will create caches at timed intervals, and then the PHP will selectively access the static files it needs. This has given me a noticeable performance boost, but I am worried about a time in which I have so much data that having to read in big files in PHP will actually be slower. I am just looking for ideas for shared hosting solutions; I am not going to get my own server anytime soon. Thanks!

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• Why would the assignment operator ever do something different than its matching constructor?

  - by Neil G

  I was reading some boost code, and came across this: inline sparse_vector &assign_temporary(sparse_vector &v) { swap(v); return *this; } template<class AE> inline sparse_vector &operator=(const sparse_vector<AE> &ae) { self_type temporary(ae); return assign_temporary(temporary); } It seems to be mapping all of the constructors to assignment operators. Great. But why did C++ ever opt to make them do different things? All I can think of is scoped_ptr?

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• Is there a way to access the locale used by gettext under windows ?

  - by phtrivier

  I have a program where i18n is handled by gettext. The program works fine, however for some reason I need to know the name of the locale used by gettext at runtime (something like 'fr_FR') under win32. I looked into gettext sources, and there is a quite frightening function that computes it on all platforms (gl_locale_name, in a C file called "localename.h/c"). However, this file does not seem to be installed alongside gettext or libintl, so I can't seem to call the function. Is there another function provided by gettext to get this value ? Or in another package (boost, glib, anything ?) (On a related note, there is a thing called std::locale in the C++ standard library, and according to the doc calling std::locale("") should create a locale with the settings of the system, unless I am mistaken ... but then the name is 'C' under windows. Is it a viable way of getting the locale name ? What I am doing wrong ?)

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• Per query relevance elevation for solr?

  - by plusplus

  I want to tune the relevance of solr search results on a per user basis - based on the number of times the user has clicked through a result before. Frequently hit items FOR THAT USER should rise to the top of their search results. Is there a way to provide custom boost/elevation for particular document ids on the query? I'm thinking in the order of ~100s of particular documents to elevate. The elevation should have no effect if the rest of the query doesn't find those documents. Alternatively, if this isn't possible, what is a sane way for setting up an alternative indexing approach that would make this possible? Could I add a field per user in the index to store their scores? I'm thinking in the order of 1000 users. The major drawback of that approach is the number of times a document would need to be reindexed (i.e. each time it was used by the user).

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• std::for_each on a member function with 1 argument

  - by Person

  I'm wondering how to implement what is stated in the title. I've tried something like... std::for_each( a.begin(), a.end(), std::mem_fun_ref( &myClass::someFunc ) ) but I get an error saying that the "term" (I"m assuming it means the 3rd argument) doesn't evaluate to a function with 1 argument, even though someFunc does take one argument - the type of the objects stored in a. I'm wondering if what I'm trying to do is possible using the standard library (I know I can do it easily using boost). P.S. Does using for_each and mem_fun_ref have any performance implications in comparison to just iterating through a manually and passing the object to someFunc?

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• What type of websites does memcached speed up

  - by Saif Bechan

  I have read this article about 400% boost of your website. This is done by a combination of nginx and memcached. The how-to part of this website is quite good, but i mis the part where it says to what types of websites this applies. I know nginx is a http engine, I need no explanation for that. I thought memcached had something to do with caching database result. However i don't understand what this has to do with the http request, can someone please explain that to me. Another question I have is for what types of websites is this used. I have a website where the important part of the website consist of data that changes often. Often being minutes. Will this method still apply to me, or should I just stick with the basic boring setup of apache and nothing else.

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• Database structure for storing Bank-like accounts and transactions

  - by user1241320

  We're in the process of adding a bank-like sub-system to our own shop. We already have customers, so each will be given a sort of account and transactions of some kind will be possible (adding to the account or subtracting from it). So we at least need the account entity, the transaction one and operations will then have to recalculate overall balances. How would you structure your database to handle this? Is there any standard bank system have to use that I could mock? By the way, we're on mysql but will also look at some nosql solution for performance boost.

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• awk / sed script to remove text

  - by radman

  Hi, I am currently needed of way to programmatically remove some text from Makefiles that I am dealing with. Now the problem is that (for whatever reason) the makefiles are being generated with link commands of -l<full_path_to_library>/<library_name> when they should be generated with -l<library_name>. So what I need is a script to find all occurrences of -l/ and then remove up to and including the next /. Example of what I'm dealing with -l/home/user/path/to/boost/lib/boost_filesystem I need it to be -lboost_filesystem As could be imagined this is a stop gap measure until I fix the real problem (on the generation side) but in the meantime it would be a great help to me if this could work and I am not too good with my awk and sed. Thanks for any help.

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• EHsc vc EHa (synchronous vs asynchronous exception handling)

  - by watson1180

  Could you give a bullet list of practical differences/implication? I read relevant MSDN article, but my understanding asynchronous exceptions is still a bit hazy. I am writing a test suite using Boost.Test and my compiler emits a warning that EHa should be enabled: warning C4535: calling _set_se_translator() requires /EHa The project itself uses only plain exceptions (from STL) and doesn't need /EHa switch. Do I have to recompile it with /EHa switch to make the test suite work properly? My feeling is that I need /EHa for the test suit only. Thank you and happy new year.

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• Store return value of function in reference C++

  - by Ruud v A

  Is it valid to store the return value of an object in a reference? class A { ... }; A myFunction() { A myObject; return A; } //myObject goes out of scope here void mySecondFunction() { A& mySecondObject = myFunction(); } Is it possible to do this in order to avoid copying myObject to mySecondObject? myObject is not needed anymore and should be exactly the same as mySecondObject so it would in theory be faster just to pass ownership of the object from one object to another. (This is also possible using boost shared pointer but that has the overhead of the shared pointer.) Thanks in advance.

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• Website content hosted with Google. Good or bad?

  - by user305052

  I recently decided to host my styles.css and various scripts on Google Docs and link them into my website. I also have all my images hosted through Picasa so that they too will load much faster and consistently across users. My site has most of its traffic from Japan, Africa, and South America, so I assume there will be a performance boost for my users since my server is hosted in Hong Kong. I (in Canada) have measured my load times to be half of what they used to be. Basically it's a free CDN for my personal stuff. I'm not too sure about all of this yet, so here's my question: what are the caveats of this setup?

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• Conditional type definitions

  - by pythonic metaphor

  I'm sure that boost has some functions for doing this, but I don't know the relevant libraries well enough. I have a template class, which is pretty basic, except for one twist where I need to define a conditional type. Here is the psuedo code for what I want struct PlaceHolder {}; template <typename T> class C{ typedef (T == PlaceHolder ? void : T) usefulType; }; How do I write that type conditional?

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• How might one implement FileTimeToSystemTime?

  - by Billy ONeal

  Hello :) I'm writing a simple wrapper around the Win32 FILETIME structure. boost::datetime has most of what I want, except I need whatever date type I end up using to interpolate with Windows APIs without issues. To that end, I've decided to write my own things for doing this -- most of the operations aren't all that complicated. I'm implementing the TimeSpan - like type at this point, but I'm unsure how I'd implement FileTimeToSystemTime. I could just use the system's built-in FileTimeToSystemTime function, except FileTimeToSystemTime cannot handle negative dates -- I need to be able to represent something like "-12 seconds". How should something like this be implemented? Billy3

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• C++ domain specific embedded language operators

  - by aaa

  hi. In numerical oriented languages (Matlab, Fortran) range operator and semantics is very handy when working with multidimensional data. For example: A(i:j,k,:n) // represents two-dimensional slice B(i:j,0:n) of A at index k unfortunately C++ does not have range operator (:). of course it can be emulated using range/slice functor, but semantics is less clean than Matlab. I am prototyping matrix/tensor domain language in C++ and am wondering if there any options to reproduce range operator. I still would like to rely on C++/prprocessor framework exclusively. So far I have looked through boost wave which might be an suitable option. is there any other means to introduce new operators to C++ DSL?

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• Potential problems porting to different architectures

  - by Brendan Long

  I'm writing a Linux program that currently compiles and works fine on x86 and x86_64, and now I'm wondering if there's anything special I'll need to do to make it work on other architectures. What I've heard is that for cross platform code I should: Don't assume anything about the size of a pointer, int or size_t Don't make assumptions about byte order (I don't do any bit shifting -- I assume gcc will optimize my power of two multiplication/division for me) Don't use assembly blocks (obvious) Make sure your libraries work (I'm using SQLite, libcurl and Boost, which all seem pretty cross-platform) Is there anything else I need to worry about? I'm not currently targeting any other architectures, but I expect to support ARM at some point, and I figure I might as well make it work on any architecture if I can. Also, regarding my second point about byte order, do I need to do anything special with text input? I read files with getline(), so it seems like that should be done automatically as well.

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• How return a std::string from C's "getcwd" function

  - by rubenvb

  Sorry to keep hammering on this, but I'm trying to learn :). Is this any good? And yes, I care about memory leaks. I can't find a decent way of preallocating the char*, because there simply seems to be no cross-platform way. const string getcwd() { char* a_cwd = getcwd(NULL,0); string s_cwd(a_cwd); free(a_cwd); return s_cwd; } UPDATE2: without Boost or Qt, the most common stuff can get long-winded (see accepted answer)

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