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  • Speeding up a group by date query on a big table in postgres

    - by zaius
    I've got a table with around 20 million rows. For arguments sake, lets say there are two columns in the table - an id and a timestamp. I'm trying to get a count of the number of items per day. Here's what I have at the moment. SELECT DATE(timestamp) AS day, COUNT(*) FROM actions WHERE DATE(timestamp) >= '20100101' AND DATE(timestamp) < '20110101' GROUP BY day; Without any indices, this takes about a 30s to run on my machine. Here's the explain analyze output: GroupAggregate (cost=675462.78..676813.42 rows=46532 width=8) (actual time=24467.404..32417.643 rows=346 loops=1) -> Sort (cost=675462.78..675680.34 rows=87021 width=8) (actual time=24466.730..29071.438 rows=17321121 loops=1) Sort Key: (date("timestamp")) Sort Method: external merge Disk: 372496kB -> Seq Scan on actions (cost=0.00..667133.11 rows=87021 width=8) (actual time=1.981..12368.186 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 32447.762 ms Since I'm seeing a sequential scan, I tried to index on the date aggregate CREATE INDEX ON actions (DATE(timestamp)); Which cuts the speed by about 50%. HashAggregate (cost=796710.64..796716.19 rows=370 width=8) (actual time=17038.503..17038.590 rows=346 loops=1) -> Seq Scan on actions (cost=0.00..710202.27 rows=17301674 width=8) (actual time=1.745..12080.877 rows=17321121 loops=1) Filter: ((date("timestamp") >= '2010-01-01'::date) AND (date("timestamp") < '2011-01-01'::date)) Total runtime: 17038.663 ms I'm new to this whole query-optimization business, and I have no idea what to do next. Any clues how I could get this query running faster?

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  • (Java) Get value of string loaded into dynamic-type object?

    - by Michael
    I'm very new to Java (~10 days), so my code is probably pretty bad, but here's what I've got: ArgsDataHolder argsData = new ArgsDataHolder(); // a class that holds two // ArrayList's where each element // representing key/value args Class thisArgClass; String thisArgString; Object thisArg; for(int i=2; i< argsString.length; i++) { thisToken = argsString[i]; thisArgClassString = getClassStringFromToken(thisToken).toLowerCase(); System.out.println("thisArgClassString: " + thisArgClassString); thisArgClass = getClassFromClassString(thisArgClassString); // find closing tag; concatenate middle Integer j = new Integer(i+1); thisArgString = getArgValue(argsString, j, "</" + thisArgClassString + ">"); thisArg = thisArgClass.newInstance(); thisArg = thisArgClass.valueOf(thisArgString); argsData.append(thisArg, thisArgClass); } The user basically has to input a set of key/value arguments into the command prompt in this format: <class>value</class>, e.g. <int>62</int>. Using this example, thisArgClass would be equal to Integer.class, thisArgString would be a string that read "62", and thisArg would be an instance of Integer that is equal to 62. I tried thisArg.valueOf(thisArgString), but I guess valueOf(<String>) is only a method of certain subclasses of Object. For whatever reason, I can't seem to be able to cast thisArg to thisArgClass (like so: thisArg = (thisArgClass)thisArgClass.newInstance();, at which point valueOf(<String>) should become accessible. There's got to be a nice, clean way of doing this, but it is beyond my abilities at this point. How can I get the value of the string loaded into a dynamically-typed object (Integer, Long, Float, Double, String, Character, Boolean, etc.)? Or am I just overthinking this, and Java will do the conversion for me? :confused:

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  • Regular Expressions, avoiding HTML tags in PHP

    - by Jason Axelrod
    I have actually seen this question quite a bit here, but none of them are exactly what I want... Lets say I have the following phrase: Line 1 - This is a TEST phrase. Line 2 - This is a <img src="TEST" /> image. Line 3 - This is a <a href="somelink/TEST">TEST</a> link. Okay, simple right? I am trying the following code: $linkPin = '#(\b)TEST(\b)(?![^<]*>)#i'; $linkRpl = '$1<a href="newurl">TEST</a>$2'; $html = preg_replace($linkPin, $linkRpl, $html); As you can see, it takes the word TEST, and replaces it with a link to test. The regular expression I am using right now works good to avoid replacing the TEST in line 2, it also avoids replacing the TEST in the href of line 3. However, it still replaces the text encapsulated within the tag on line 3 and I end up with: Line 1 - This is a <a href="newurl">TEST</a> phrase. Line 2 - This is a <img src="TEST" /> image. Line 3 - This is a <a href="somelink/TEST"><a href="newurl">TEST</a></a> link. This I do not want as it creates bad code in line 3. I want to not only ignore matches inside of a tag, but also encapsulated by them. (remember to keep note of the / in line 2)

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  • Implementing comparision operators via 'tuple' and 'tie', a good idea?

    - by Xeo
    (Note: tuple and tie can be taken from Boost or C++11.) When writing small structs with only two elements, I sometimes tend to choose a std::pair, as all important stuff is already done for that datatype, like operator< for strict-weak-ordering. The downsides though are the pretty much useless variable names. Even if I myself created that typedef, I won't remember 2 days later what first and what second exactly was, especially if they are both of the same type. This gets even worse for more than two members, as nesting pairs pretty much sucks. The other option for that is a tuple, either from Boost or C++11, but that doesn't really look any nicer and clearer. So I go back to writing the structs myself, including any needed comparision operators. Since especially the operator< can be quite cumbersome, I thought of circumventing this whole mess by just relying on the operations defined for tuple: Example of operator<, e.g. for strict-weak-ordering: bool operator<(MyStruct const& lhs, MyStruct const& rhs){ return std::tie(lhs.one_member, lhs.another, lhs.yet_more) < std::tie(rhs.one_member, rhs.another, rhs.yet_more); } (tie makes a tuple of T& references from the passed arguments.) Edit: The suggestion from @DeadMG to privately inherit from tuple isn't a bad one, but it got quite some drawbacks: If the operators are free-standing (possibly friends), I need to inherit publicly With casting, my functions / operators (operator= specifically) can be easily bypassed With the tie solution, I can leave out certain members if they don't matter for the ordering Are there any drawbacks in this implementation that I need to consider?

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  • License key pattern detection?

    - by Ricket
    This is not a real situation; please ignore legal issues that you might think apply, because they don't. Let's say I have a set of 200 known valid license keys for a hypothetical piece of software's licensing algorithm, and a license key consists of 5 sets of 5 alphanumeric case-insensitive (all uppercase) characters. Example: HXDY6-R3DD7-Y8FRT-UNPVT-JSKON Is it possible (or likely) to extrapolate other possible keys for the system? What if the set was known to be consecutive; how do the methods change for this situation, and what kind of advantage does this give? I have heard of "keygens" before, but I believe they are probably made by decompiling the licensing software rather than examining known valid keys. In this case, I am only given the set of keys and I must determine the algorithm. I'm also told it is an industry standard algorithm, so it's probably not something basic, though the chance is always there I suppose. If you think this doesn't belong in Stack Overflow, please at least suggest an alternate place for me to look or ask the question. I honestly don't know where to begin with a problem like this. I don't even know the terminology for this kind of problem.

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  • What is the point of having a key_t if what will be the key to access shared memory is the return value of shmget()?

    - by devoured elysium
    When using shared memory, why should we care about creating a key key_t ftok(const char *path, int id); in the following bit of code? key_t key; int shmid; key = ftok("/home/beej/somefile3", 'R'); shmid = shmget(key, 1024, 0644 | IPC_CREAT); From what I've come to understand, what is needed to access a given shared memory is the shmid, not the key. Or am I wrong? If what we need is the shmid, what is the point in not just creating a random key every time? Edit @link text one can read: What about this key nonsense? How do we create one? Well, since the type key_t is actually just a long, you can use any number you want. But what if you hard-code the number and some other unrelated program hardcodes the same number but wants another queue? The solution is to use the ftok() function which generates a key from two arguments. Reading this, it gives me the impression that what one needs to attach to a shared-memory block is the key. But this isn't true, is it? Thanks

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  • What's wrong (or right) with this JS Object Pattern?

    - by unsane1
    Here's an example of the pattern I'm using in my javascript objects these days (this example relies on jQuery). http://pastie.org/private/ryn0m1gnjsxdos9onsyxg It works for me reasonably well, but I'm guessing there's something wrong, or at least sub-optimal about it, I'm just curious to get people's opinions. Here's a smaller, inline example of it: sample = function(attach) { // set internal reference to self var self = this; // public variable(s) self.iAmPublic = true; // private variable(s) var debug = false; var host = attach; var pane = { element: false, display: false } // public function(s) self.show = function() { if (!pane.display) { position(); $(pane.element).show('fast'); pane.display = true; } } self.hide = function() { if (pane.display) { $(pane.element).hide('fast'); pane.display = false; } } // private function(s) function init () { // do whatever stuff is needed on instantiation of this object // like perhaps positioning a hidden div pane.element = document.createElement('div'); return self; } function position() { var h = { 'h': $(host).outerHeight(), 'w': $(host).outerWidth(), 'pos': $(host).offset() }; var p = { 'w': $(pane.element).outerWidth() }; $(pane.element).css({ top: h.pos.top + (h.h-1), left: h.pos.left + ((h.w - p.w) / 2) }); } function log () { if (debug) { console.log(arguments); } } // on-instantiation let's set ourselves up return init(); } I'm really curious to get people's thoughts on this.

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  • Google Anlytics event not firing

    - by yar1
    I am not getting and event data in GA. I installed Google Analytics Debugger Chrome extension and I see nothing happening (same goes when looking at Network panel in developer tools). I Googled it and read many (many) other answers and it looks like I'm doing things right. Page views, etc. are registering correctly... I have this code as the last thing before my closing tag: <script> (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) })(window,document,'script','//www.google-analytics.com/analytics.js','ga'); ga('create', 'UA-MYREALCODE', 'mybna.net'); ga('send', 'pageview'); var _gaq = _gaq || []; _gaq.push(['_setAccount', 'UA-MYREALCODE']); _gaq.push(['_trackPageview']); </script> My event handlers are done using jQuery, all inside an external js file, loaded before the closing tag. For example: $(function () { $('#show-less').click(function (e) { pbr.showHideMore(e); _gaq.push(['_trackEvent', 'ShowMore', 'Hide', 'top button']); }); }); Any ideas anyone?

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  • get random password with puppet function

    - by ninja-2
    I have a function that allow me to generate random password. My function is working well without a puppetmaster. When i tried with a master an error appear when I called the function : Error 400 on SERVER: bad value for range Here is my function module Puppet::Parser::Functions newfunction(:get_random_password, :type => :rvalue, :doc => <<-EOS Returns a random password. EOS ) do |args| raise(Puppet::ParseError, "get_random_password(): Wrong number of arguments " + "given (#{args.size} for 1)") if args.size != 1 specials = ((33..33).to_a + (35..38).to_a + (40..47).to_a + (58..64).to_a + (91..93).to_a + (95..96).to_a + (123..125).to_a).pack('U*').chars.to_a numbers = (0..9).to_a alphal = ('a'..'z').to_a alphau = ('A'..'Z').to_a length = args[0] CHARS = (alphal + specials + numbers + alphau) pwd = CHARS.sort_by { rand }.join[0...length] return pwd end end The function is called in both case with $pwd = get_random_password(10). When I specified the length directly in the function to 10 for example. the password is well generated in master mode. Have you any idea why i can't specify the lentgth value ? Thanks for any help.

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  • Why would gnu ld link order causes Signal 11 (SEGV) on startup?

    - by Benoit
    We are building a large application in C++ that includes the use of many (static) libraries. We have a problem where the application crashes on startup with a Signal 11, before we even reach main. After much debugging, we have observed that if we explicitly reference an object file so its link order is early, the program crashes on startup. If the file is referenced later (or not referenced at all), the program does not crash. To be clear, there is NO code invoked directly from this object file. However, as it is C++, there might be static objects that do get constructed (it's a CORBA IDL generated file). We use the -Wl,--start-group ... --end-group arguments to multi-pass link the symbols since the libraries are interdependent. Here is a representation of what I mean. This is what the linker's object file order is: Order 1 Order 2 Order 3 foo.o foo.o foo.o ... ... ... main.o main.o main.o crasher.o libA.o libA.o libA.o LibB.o LibB.o LibB.o LibC.o LibC.o LibC.o crasher.o Results: NO CRASH NO CRASH CRASH Does any one have an idea why the linkage order has an effect on the crash? It would be nice if we could force the crasher.o to link later, but we're really after an explanation. Also, is there a way to force the linker to place crasher.o towards the end? Just to add to the fun, in actuality, crasher.o is part of a Library in the --start/--end-group.

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  • swap! alter and alike

    - by mekka
    Hello, I am having a problem understanding how these functions update the underlying ref, atom etc. The docs say: (apply f current-value-of-identity args) (def one (atom 0)) (swap! one inc) ;; => 1 So I am wondering how it got "expanded" to the apply form. It's not mentioned what exactly 'args' in the apply form is. Is it a sequence of arguments or are these separate values? Was it "expanded" to: (apply inc 0) ; obviously this wouldnt work, so that leaves only one possibility (apply inc 0 '()) (swap! one + 1 2 3) ;; #=> 7 Was it: (apply + 1 1 2 3 '()) ;or (apply + 1 [1 2 3]) (def two (atom [])) (swap! two conj 10 20) ;; #=> [10 20] Was it: (apply conj [] [10 20]) ;or (apply conj [] 10 20 '()) If I swap with a custom function like this: (def three (atom 0)) (swap! three (fn [current elem] (println (class elem))) 10) ;;#=> java.Lang.Integer Which means that the value '10' doesnt magically get changed into a seq '(10) and leads me to the conclusion, that it gets "expanded" to: (apply f current-value-of-identity arg1 arg2 arg3... '()) Is that a correct assumption and the docs are simply lacking a better description?

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  • Why can't these generic type parameters be inferred?

    - by Jon M
    Given the following interfaces/classes: public interface IRequest<TResponse> { } public interface IHandler<TRequest, TResponse> where TRequest : IRequest<TResponse> { TResponse Handle(TRequest request); } public class HandlingService { public TResponse Handle<TRequest, TResponse>(TRequest request) where TRequest : IRequest<TResponse> { var handler = container.GetInstance<IHandler<TRequest, TResponse>>(); return handler.Handle(request); } } public class CustomerResponse { public Customer Customer { get; set; } } public class GetCustomerByIdRequest : IRequest<CustomerResponse> { public int CustomerId { get; set; } } Why can't the compiler infer the correct types, if I try and write something like the following: var service = new HandlingService(); var request = new GetCustomerByIdRequest { CustomerId = 1234 }; var response = service.Handle(request); // Shouldn't this know that response is going to be CustomerResponse? I just get the 'type arguments cannot be inferred' message. Is this a limitation with generic type inference in general, or is there a way to make this work?

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  • C Map String to Function

    - by Scriptonaut
    So, I'm making a Unix minishell, and have come to a roadblock. I need to be able to execute built-in functions, so I made a function: int exec_if_built_in(char **args) It takes an array of strings(the first being the command, and the rest being arguments). For non built-in commands I simply use something like execvp, however I need to find a way to map the first string to a function. I was thinking of making two arrays, one of strings, and another with their corresponding function pointers. However, since many of these functions will be different(return and accept different things), this approach won't work. I also thought of making an array of structs with a name property and a function pointer property, however once again due to the varied nature of the functions I'll be using, this won't work. So, what's the best way to execute a function based on the input of a string? How do I map a string to a certain function? I'm not very familiar with function pointers so I may be missing something. Thank you guys for the help :)

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  • Dynamic WebService implementation

    - by chardex
    I have a set of different interfaces and I need to give them access via web services. I have implemented this task in .NET as follows: dynamically generated interface implementation on the IL, marked methods with WebMethod annotation, and in *.asmx handler called generated stub. More needs to be able to change the method signatures (eg change the type of certain argument or add new arguments), ie not always explicitly implement an interface, and use it as a decorator pattern. Example: interface ISomeService { void simpleMetod (String arg1); void customMetod (CusomType arg1, Integer arg2); } // Need to dynamically generate such class @WebService class SomeWebService { private ISomeService someService = new SomeServiceImpl (); @WebMethod public void simpleMethod (String arg1) { someService.simpleMethod (arg1); } @WebMethod public void customMethod (String arg1, Integer arg2) { someService.customMethod (CusomType.fromString (arg1), arg2); } } Interfaces such as ISomeService quite a lot. And manually write code like this I don't want. I work with Java recently, what technology/libraries should be used to solve such task. Thanks.

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  • recursive wget with hotlinked requisites

    - by dongle
    I often use wget to mirror very large websites. Sites that contain hotlinked content (be it images, video, css, js) pose a problem, as I seem unable to specify that I would like wget to grab page requisites that are on other hosts, without having the crawl also follow hyperlinks to other hosts. For example, let's look at this page https://dl.dropbox.com/u/11471672/wget-all-the-things.html Let's pretend that this is a large site that I would like to completely mirror, including all page requisites – including those that are hotlinked. wget -e robots=off -r -l inf -pk ^^ gets everything but the hotlinked image wget -e robots=off -r -l inf -pk -H ^^ gets everything, including hotlinked image, but goes wildly out of control, proceeding to download the entire web wget -e robots=off -r -l inf -pk -H --ignore-tags=a ^^ gets the first page, including both hotlinked and local image, does not follow the hyperlink to the site outside of scope, but obviously also does not follow the hyperlink to the next page of the site. I know that there are various other tools and methods of accomplishing this (HTTrack and Heritrix allow for the user to make a distinction between hotlinked content on other hosts vs hyperlinks to other hosts) but I'd like to see if this is possible with wget. Ideally this would not be done in post-processing, as I would like the external content, requests, and headers to be included in the WARC file I'm outputting.

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  • Shell Scripting: Generating output file name in script and then writing to it

    - by NewShellScripter
    Hello, I have a shell script where a user passes different sizes as command line arguments. For each of those sizes, I want to perform some task, then save the output of that task into a .txt file with the size in the name. How can I take the command line passed and make that part of a stringname for the output file? I save the output file in a directory specified by another command line argument. Perhaps an example will clear it up. In the foor lop, the i value represents the command line argument I need to use, but $$i doesnt work. ./runMe arg1 arg2 outputDir [size1 size2 size3...] for ((i=4; i<$#; i++ )) do ping -s $$i google.com >> $outputDir/$$iresults.txt done I need to know how to build the $outputDir/$$iresults.txt string. Also, the ping -s $$i doesnt work. Its like I need two levels of replacement. I need to replace the $[$i] inner $i with the value in the loop, like 4 for ex, making it $4. Then replace $4 with the 4th command line argument! Any help would be greatly appreciated. Thanks!

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  • Retrieving the first picture with a HTML parser

    - by justin01
    Hey guys, (Not a native english speaker) I'm doing a personal project in PHP in which I use the Simple HTML Parser to parse the HTML of a given URL and retrieve the first image in a DIV that have a specific ID or class (maincontent, content, main, wrapper, etc. - it's all in an array) and ignore ads. The goal is to take this image and make a thumbnail with it, pretty much like on Digg and others. I thought everything was working fine until I tried my script with the website Snopes ("http://www.snopes.com/photos/animals/luckycoyote.asp" <- this page more exactly). The source of the first image it gets is: " graphics/luckycoyote1.jpg ". So far, to correct this problem I created a little function that gets the domain name of the given URL and insert it before the IMG's source attribute. So for sites like Snopes.com, it gives me: "http://www.snopes.com/graphics/luckycoyote1.jpg" ... while the real URL for this image is "http://www.snopes.com*/photos/animals/graphics/luckycoyote1.jpg*" (or, more precisely: " http://graphics1.snopes.com/photos/animals/graphics/luckycoyote1.jpg " - note the subdomain here). So my main question is: how can I externally/dynamically retrieve the full URL address of an image ("absolute path") when I am only given the "relative path"? I'm pretty sure this is possible, since when I paste the link in Facebook's "What are you doing?" field for example, it gives me the correct path to the image while on the website, the source of the image is only (example) "image/photo/example.jpg". Thank you for your time.

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  • Are multiline queries sql-injection safe?

    - by acmatos
    This might be a stupid question. Or maybe my hacking skills are limited (I don't practice them at all). I have a query that looks like this: <?php $query =<<<eot SELECT table_x.field1, table_x.field2, table_y.*, table_z.field4 FROM ( SELECT ... ) as table_y LEFT JOIN table_x ON table_x.field1 = table_y.field_x LEFT JOIN table_z ON table_z.field1 = table_y.field_z WHERE table_x.field3 = '$something' AND table_z.field4 = '1' AND table_z.field5 = '2' eot; ?> I have a lot of other tests on $something before it gets used, like $something = explode(' ',$something); (which later result in a string) none of them intend to prevent injection but they make it hard for the given injection to get as is to the actual query. However, there are ways. We all know how easy it is to replace a space for something else which is still valid.. So, it's not really a problem to make a potentially harmful piece of SQL reach that $something... But is there any way to comment the rest of the original query string if it is multi-line? I can comment AND table_z.field4 = '1' using ;-- but can't comment the following AND table_z.field5 = '2' Is it possible to open a multi-line comment /* without closing it or something looked like and therefore allow the injection to ignore the multi-line query?

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  • Use a table as container or not?

    - by Camran
    I have created my entire website by using a main table, and having the content inside the table. Some ppl suggest this is wrong, and I would like to know what to do specifically in my situation. On my index.html I have a <table align="center"> and then all content in it. Now the content is in form of DIVS and they all have relative positioning, so they are relative to the table. For example: <table align="center"> <tr> <td> <div style="position:relative; left:14px; top:50px;"> CONTENT HERE... (Form, divs, images) </div> </td> </tr> </table> I have just gotten to the stage of browser compatibility. Without making any changes whatsoever, my website works perfect in FF, SAFARI, Chrome and Opera. Only trouble with IE. So for my Q, if you where me, would you change my layout and remove the tables, and instead use alot more css and alot more DIVS, or would you go with what I have? And please if you answer me, don't just provide me with the answer, but also a "why" that is... in other words, give me arguments and facts... Thanks

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  • std::bind overload resolution

    - by bpw1621
    The following code works fine #include <functional> using namespace std; using namespace std::placeholders; class A { int operator()( int i, int j ) { return i - j; } }; A a; auto aBind = bind( &A::operator(), ref(a), _2, _1 ); This does not #include <functional> using namespace std; using namespace std::placeholders; class A { int operator()( int i, int j ) { return i - j; } int operator()( int i ) { return -i; } }; A a; auto aBind = bind( &A::operator(), ref(a), _2, _1 ); I have tried playing around with the syntax to try and explicitly resolve which function I want in the code that does not work without luck so far. How do I write the bind line in order to choose the call that takes the two integer arguments?

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  • Renaming the argument name in JAX-WS

    - by user182944
    I created a web service using JAX-WS in RSA 7.5 and Websphere 7 using bottom-up approach. When I open the WSDL in SOAP UI, then the arguments section is appearing like this: <!--Optional--> <arg0> <empID>?</empId> </arg0> <!--Optional--> <arg1> <empName>?</empName> </arg1> <!--Optional--> <arg2> <empAddress>?</empAddress> </arg2> <!--Optional--> <arg3> <empCountry>?</empCountry> </arg3> The service method takes the above 4 elements as the parameters to return the employee details. 1) I want to rename this arg0, arg1, and so on with some valid names. 2) I want to remove the <!--optional--> present above the arg tags. (For removing the <!--optional--> from elements name, I used @XMLElement(required=true)). But I am not sure where exactly to use this annotation in this case :( Please help. Regards,

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  • Template Syntax in C++

    - by Crystal
    I don't understand templates really and was trying to run a simple find the minimum for ints, doubles, chars. First question, why is template<typename T> sometimes used, and other times template<>? Second question, I do not know what I am doing wrong with the following code below: #include <iostream> template <typename T> T minimum(T arg1, T arg2) { return arg1 < arg2 ? arg1 : arg2; } template <typename T> // first I tried template <> instd of above, but wasn't sure the difference T minimum<const char *>(const char *arg1, const char *arg2) { return strcmp(arg1, arg2) ? arg2 : arg1; } int main() { std::cout << minimum<int>(4, 2) << '\n'; std::cout << minimum<double>(2.2, -56.7) << '\n'; std::cout << minimum(2.2, 2) << '\n'; } Compile Errors: error C2768: 'minimum' : illegal use of explicit template arguments error C2783: 'T minimum(const char *,const char *)' : could not deduce template argument for 'T' : see declaration of 'minimum' : error C2782: 'T minimum(T,T)' : template parameter 'T' is ambiguous : see declaration of 'minimum' Third, in getting familiar with separating .h and .cpp files, if I wanted this minimum() function to be a static function of my class, but it was the only function in that class, would I have to have a template class as well? I originally tried doing it that way instead of having it all in one file and I got some compile errors as well that I can't remember right now and was unsure how I would do that. Thanks!

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  • Allocating 32-bit integer arrays in 64-bit machines

    - by Shredderroy
    I have a 64-bit i7 machine. Suppose I allocate memory for n 32-bit integers. How many physical registers will actually be used in the allocation: n, or n/2? I tried to write the following simple programme to find out. #include <iostream> #include <cstdlib> using namespace std; int main (int argc, char *argv[]) { int a[4]; cout << &a[0] << "\t" << &a[3] << endl; cin.ignore (1); return 0; } // End main () The output is: 0018FA04 0018FA10 They seem further apart than they should be. Why aren't the addresses 04 and 07? And does this mean that the system is actually allocating four (or more) integers, instead of packing the four 32-bit integers into two 64-bit registers? Thanks in advance for your help.

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  • for loop vs std::for_each with lambda

    - by Andrey
    Let's consider a template function written in C++11 which iterates over a container. Please exclude from consideration the range loop syntax because it is not yet supported by the compiler I'm working with. template <typename Container> void DoSomething(const Container& i_container) { // Option #1 for (auto it = std::begin(i_container); it != std::end(i_container); ++it) { // do something with *it } // Option #2 std::for_each(std::begin(i_container), std::end(i_container), [] (typename Container::const_reference element) { // do something with element }); } What are pros/cons of for loop vs std::for_each in terms of: a) performance? (I don't expect any difference) b) readability and maintainability? Here I see many disadvantages of for_each. It wouldn't accept a c-style array while the loop would. The declaration of the lambda formal parameter is so verbose, not possible to use auto there. It is not possible to break out of for_each. In pre- C++11 days arguments against for were a need of specifying the type for the iterator (doesn't hold any more) and an easy possibility of mistyping the loop condition (I've never done such mistake in 10 years). As a conclusion, my thoughts about for_each contradict the common opinion. What am I missing here?

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  • (Java) Is there a type of object that can handle anything from primitives to arrays?

    - by Michael
    I'm pretty new to Java, so I'm hoping one of you guys knows how to do this. I'm having the user specify both the type and value of arguments, in any XML-like way, to be passed to methods that are external to my application. Example: javac myAppsName externalJavaClass methodofExternalClass [parameters] Of course, to find the proper method, we have to have the proper parameter types as the method may be overloaded and that's the only way to tell the difference between the different versions. Parameters are currently formatted in this manner: (type)value(/type), e.g. (int)71(/int) (string)This is my string that I'm passing as a parameter!(/string) I parse them, getting the constructor for whatever type is indicated, then execute that constructor by running its method, newInstance(<String value>), loading the new instance into an Object. This works fine and dandy, but as we all know, some methods take arrays, or even multi-dimensional arrays. I could handle the argument formatting like so: (array)(array)(int)0(/int)(int)1(/int)(/array)(array)(int)2(/int)(int)3(/int)(/array)(/array)... or perhaps even better... {{(int)0(/int)(int)1(/int)}{(int)2(/int)(int)3(/int)}}. The question is, how can this be implemented? Do I have to start wrapping everything in an Object[] array so I can handle primitives, etc. as argObj[0], but load an array as I normally would? (Unfortunately, I would have to make it an Object[][] array if I wanted to support two-dimensional arrays. This implementation wouldn't be very pretty.)

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