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  • Why do you sometimes need to write <typename T> instead of just <T> ?

    - by StackedCrooked
    I was reading the Wikipedia article on SFINAE and encountered following code sample: struct Test { typedef int Type; }; template < typename T > void f( typename T::Type ) {} // definition #1 template < typename T > void f( T ) {} // definition #2 void foo() { f< Test > ( 10 ); //call #1 f< int > ( 10 ); //call #2 without error thanks to SFINAE } Now I've actually written code like this before, and somehow intuitively I knew that I needed to type "typename T" instead of just "T". However, it would be nice to know the actual logic behind it. Anyone care to explain?

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  • c++: what is a good idea for a list of strings?

    - by John
    I simply want to build an RPG and make it as neat as possible, I wish to define a pile of strings which I may want to edit later, so I tried something like this: enum {MSG_INIT = "Welcome to ...", MSG_FOO = "bar"}; But I just get errors, such as that MSG_INIT is not an integer! Why must it not be a string, are that what enums are only for? What do you think is the best way to define a pile of strings? In a struct called msg or something? I'm kinda new to all this so I'd really appreciate small examples.

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  • c++ - FIFO implementation

    - by Narek
    While implementing a FIFO I have used the following structure: struct Node { T info_; Node* link_; Node(T info, Node* link=0): info_(info), link_(link) {} }; I think this a well known trick for lots of STL containers (for example for List). Is this a good practice? What it means for compiler when you say that Node has a member with a type of it's pointer? Is this a kind of infinite loop? And finally, if this is a bad practice, how I could implement a better FIFO.

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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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  • Can the template parameters of a constructor be explicitly specified?

    - by sth
    A constructor of a class can be a template function. At the point where such a constructor is called, the compiler usually looks at the arguments given to the constructor and determines the used template parameters from them. Is there also some syntax to specify the template parameters explicitly? A contrived example: struct A { template<typename T> A() {} }; Is there a way to instantiate this class? What is the syntax to explicitly specify the constructor's template parameters? My use case would be a problem were the compiler doesn't seem to find the correct templated constructor. Explicitly specifying the template parameters would probably generate more useful error messages or even resolve the problem.

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  • Can a method return an NSRange?

    - by Dan Donaldson
    I have a method that returns an NSRange. When I call this method from outside the class I get a compile error. NSRange tmpRange; tmpRange = [phrase rangeInString:searchString forString:theLetter goingForward:YES]; return tmpRange.location == -1; in the .h file: #import <Foundation/Foundation.h> @interface Phrase : NSObject { } - (NSRange) rangeInString:(NSString *) tgt forString:(NSString *) find goingForward:(BOOL) fwd; @end This method is called within the Phrase object by other methods without problems. The compiler says 'incompatible types in assignment'. Can anyone explain this to me? I assume it has to do with returning an NSRange/struct type value generated outside the object, but I don't know why it works in one place and not the other.

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  • Why does a non-constant offsetof expression work?

    - by Chris J. Kiick
    Why does this work: #include <sys/types.h> #include <stdio.h> #include <stddef.h> typedef struct x { int a; int b[128]; } x_t; int function(int i) { size_t a; a = offsetof(x_t, b[i]); return a; } int main(int argc, char **argv) { printf("%d\n", function(atoi(argv[1]))); } If I remember the definition of offsetof correctly, it's a compile time construct. Using 'i' as the array index results in a non-constant expression. I don't understand how the compiler can evaluate the expression at compile time. Why isn't this flagged as an error?

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  • how to arrange the checkboxes in 3/3 format on a layout of a form

    - by anwaar
    hi there can anyone plz tell me how to arrange the list of checkboxes of cuisines label which is retrived from the data base and when it is displaying it is not in the order coming side by side all together i want it to be displayed in a 3 by 3 format.here is the code for that: <div id="frmform"> <form name="frmrestaurant" id="frmrestaurant" method="post" onsubmit="" enctype="multipart/form-data"> <p class="msgsignup">Add Restaurant</p> <div id="iderror"></div> <div class="topinputs"> <div> <label for="restaurant_name" class="name">Restaurant Name :</label><input type="text" name="restaurant_name" size="32" id="restaurant_name" value="<?php echo $row->restaurant_name; ?>" class="validate[required,custom[onlyLetter],length[0,100]] text-input" /> </div> </div> <div> <label for="website" class="name">Website :</label><input size="32" type="text" name="website" id="website" value="<?php echo $row->website; ?>" class="validate[required,length[0,100]] text-input" /> </div> <div> <label for="budget" class="name">Budget :</label> <?php echo $this->lists['budget'];?> </div> <div> <label for="idcuisine" class="cuisine" >Cuisine:</label> <?php echo $this->lists['cuisine'] ;?> <div> <label for="idcategory" class="category">Category:</label> <?php echo $this->lists['category'];?> </div> the lists of cuisine and category is not displaying properly. thanks.

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  • Jquery image slider window resize scaling issue

    - by eb_Dev
    Hi, I have created image gallery slider, the images of which scale with the window size. My problem is I can't seem to create the right formula to ensure that the slider is at the right position when the window is scaled. If I am at the first image and the slider 'left' offset is 0 then the scaling works fine and my offset is correct, however when I am on image two and my slider is offset by say -1500 and then the window is resized, the slider is then at the wrong offset. Taking this into account I figured I could just add / subtract the new window size difference from the slider offset and therefore have everything in the right position. I was wrong. It works for the first two images but then If I am at the end of my slider on the last image I get a nice big gap between the end of the last image and the border of the page. Can someone please show my where I am going wrong please? I've spent days on this :( The relevant code is as follows: $(window).bind('resize', function(event, delta) { /* Resize work images - resizes all to document width */ resizeWorkImages('div.page.work div#work ul'); /* Position slider controls */ positionSliderControls(); /* Get the difference between the old window width and the new */ var windowDiff = (gLastWindowWidth - $(window).width()) * -1; /* Apply difference to slider left position */ var newSliderLeftPos = stripPx($('div.page.work div#work ul').css('left')) - windowDiff; /* Apply to slider */ $('div.page.work div#work ul').css('left',newSliderLeftPos+'px') /* Update gSlider settings */ gSlider.update(); /* Record new window width */ gLastWindowWidth = $(window).width(); }); Thanks, eb_dev

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  • C++: Copying to dereferenced pointer...

    - by bbb
    Hi. I currently have a weird problem with a program segfaulting but im not able to spot the error. I think the problem boils down to this. struct S {int a; vector<sometype> b;} S s1; // fill stuff into a and b S* s2 = new S(); *s2 = s1; Could it be that the final copying is illegal in some way? Im really confused right now... Thanks

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  • What's the simplest way of defining lexicographic comparison for elements of a class?

    - by the_mandrill
    If I have a class that I want to be able to sort (ie support a less-than concept), and it has several data items such that I need to do lexicographic ordering then I need something like this: struct MyData { string surname; string forename; bool operator<(const MyData& other) const { return surname < other.surname || (surname==other.surname && forename < other.forename); } }; This becomes pretty unmanageable for anything with more than 2 data members. Are there any simpler ways of achieving it? The data members may be any Comparable class.

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  • .NET List Thread-Safe Implementation Suggestion needed

    - by Bamboo
    .Net List class isn't thread safe. I hope to achieve the minimal lock needed and yet still fulfilling the requirement such that as for reading, phantom record is allowed, and for writing, they must be thread-safe so there won't be any lost updates. So I have something like public static List<string> list = new List<string>(); In Methods that have **List.Add**/**List.Remove** , I always lock to assure thread safety lock (lockHelper) { list.Add(obj); or list.Remove(obj); } In Methods that requires **List Reading** I don't care about phantom record so I go ahead to read without any locking. In this case. Return a bool by checking whether a string had been added. if (list.Count() != 0) { return list.Contains("some string") } All I did was locking write accesses, and allow read accesses to go through without any locking. Is my thread safety idea valid? I understand there is List size expansion. Will it be ok? My guess is that when a List is expanding, it may uses a temp. list. This is ok becasue the temp list size will always have a boundary, and .Net class is well implemented, ie. there shouldn't be any indexOutOfBound or circular reference problems when reading was caught in updates.

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  • Structure within union and bit field

    - by java
    #include <stdio.h> union u { struct st { int i : 4; int j : 4; int k : 4; int l; } st; int i; } u; int main() { u.i = 100; printf("%d, %d, %d", u.i, u.st.i, u.st.l); } I'm trying to figure out the output of program. The first outputs u.i = 100 but I can't understand the output for u.st.i and u.st.l. Please also explain bit fields.

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  • Redundant naming in C/C++ typedefs/structs

    - by bloomy
    #include <stdio.h> #include <string.h> const int NAMELEN=30; const int MAXCLASSSIZE=10; typedef struct StudentRec { char lastname[NAMELEN]; char firstname[NAMELEN]; long int ID; int finalmark; }Student; I'm new to coding..and I have a question about why there is Student; after the bracket.. is it a format that we have to follow.

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  • How to know if the argument that is passed to the function is a class, union or enum in c++?

    - by Narek
    I want to define an operator<< for all enums, to cout the value and print that it is an enum like this: code: enum AnyEnum{A,B,C}; AnyEnum enm = A; cout << enm <<endl; output: This is an enum which has a value equal to 0 I know a way of doing this with Boost library by using is_enum struct. But I don’t understand how it works. So that's why, in general, I am interested how to identify if the veriable is a class type, union type or an enum (in compile time).

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  • PHP is truncating MSSQL Blob data (4096b), even after setting INI values. Am I missing one?

    - by Dutchie432
    I am writing a PHP script that goes through a table and extracts the varbinary(max) blob data from each record into an external file. The code is working perfectly, except when a file is over 4096b - the data is truncated at exactly 4096. I've modified the values for mssql.textlimit, mssql.textsize, and odbc.defaultlrl without any success. Am I missing something here? <?php ini_set("mssql.textlimit" , "2147483647"); ini_set("mssql.textsize" , "2147483647"); ini_set("odbc.defaultlrl", "0"); include_once('common.php'); $id=$_REQUEST['i']; $q = odbc_exec($connect, "Select id,filename,documentBin from Projectdocuments where id = $id"); if (odbc_fetch_row($q)){ echo "Trying $filename ... "; $fileName="projectPhotos/docs/".odbc_result($q,"filename"); if (file_exists($fileName)){ unlink($fileName); } if($fh = fopen($fileName, "wb")) { $binData=odbc_result($q,"documentBin"); fwrite($fh, $binData) ; fclose($fh); $size = filesize($fileName); echo ("$fileName<br />Done ($size)<br><br>"); }else { echo ("$fileName Failed<br>"); } } ?> OUTPUT Trying ... projectPhotos/docs/file1.pdf Done (4096) Trying ... projectPhotos/docs/file2.zip Done (4096) Trying ... projectPhotos/docsv3.pdf Done (4096) etc..

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  • Why is this C++ code working ?

    - by gregseth
    Why doesn't the program segfault on the p->info() call? struct A { int info() { retrun (this) ? 1 : -1; } }; int main() { A* p = NULL; if (p->info() == 1) { cout << "I'm alive!" << endl; } else { cout << "I'm NULL..." << endl; } return 0; }

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  • C++: how serialize/deserialize objects without any library?

    - by Winte Winte
    I try to understand how serializing/deserializing works in c++, so I want to do that without any libs. But I really stuck with that. I start with simple objects but when I try to deserilize a vector I understand that I can't get a vector without if I don't write it size before. Moreover, I don't know which format of file I should choose because if digits will be existed before size of vector I haven't chance to read it right. However it is only the vector but I also want to do that with classes and map container. My task is serialize/deserialize a objects as this: PersonInfo { unsigned int age_; string name_; enum { undef, man, woman } sex_; } Person : PersonInfo { vector<Person> children_; map<string, PersonInfo> addrBook_; } Currently I know how to serialize simple objects in way as this: vector<PersonInfo> vecPersonInfo; vecPersonInfo.push_back(*personInfo); vecPersonInfo.push_back(*oneMorePersonInfo); ofstream file("file", ios::out | ios::binary); if (!file) { cout<<"can not open file"; } else { vector<PersonInfo>::const_iterator iterator = vecPersonInfo.begin(); for (; iterator != vecPersonInfo.end(); iterator++) { file<<*iterator; } Could you please suggest how I can do this for this conplex object or a good tutorial that explain it clearly?

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  • Figure and figcaption figures shrink images

    - by Why Not
    I'm attempting to use the figure and figcaption tags to varying success. Someone suggested a great CSS method to get rid of the figure margin and also link up the caption with the image. The problem: all images shrink to an extremely small size. Not sure how to rectify this. These are user-submitted images using Django so they vary in size. But currently, using these fixes, all of these shrink with a caption that does fit the image but defeats the purpose as it results in a tiny image with a caption with an even width. {% if story.pic %} <h2>Image</h2> <figure> <img class="image"src="{{ story.pic.url }}" alt="some_image_alt_text"/> {% if story.caption %} <figcaption>{{story.caption}}</figcaption> {% endif %} </figure> {% endif %} figure {margin:0; display:table; width:1px;} figcaption {display:table-row;}

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  • Issues with an image link

    - by user1462362
    Two days ago I spontaneously bought myself a domain. The day before that, I hardly even knew what a domain really was. Since then, I've been trying to teach myself HTML for the very first time. Basically what I'm trying to say is, I'm very new - and will probably be poor in my explanations. I just succeeded in making an 'image-button', sorta. It's where I make a button-like image and then use it as navigation on my website (just like a regular link). My issue is that the link 'border' itself is bigger than the image, so you can press an inch outside the image itself and it will work. How do I make the invisible link 'border' the same size as the button? This is my site: http://www.djeveln.com On the test page (djeveln.com/test) is where I test things. There's the button I'm talking about, in case you can't understand my explanation very well. Here's my HTML: Here is the CSS I use for the image position and size: img.TestButton { /* Dette linker til selve størrelsen av knappen (bildet)*/ position: absolute; width: 100px; height: 75px; top: 400px; right: 250px; } Hope you can help me! :P

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  • Hive performance increase

    - by Sagar Nikam
    I am dealing with a database (2.5 GB) having some tables only 40 row to some having 9 million rows data. when I am doing any query for large table it takes more time. I want results in less time small query on table which have 90 rows only-- hive> select count(*) from cidade; Time taken: 50.172 seconds hdfs-site.xml <configuration> <property> <name>dfs.replication</name> <value>3</value> <description>Default block replication. The actual number of replications can be specified when the file is created. The default is used if replication is not specified in create time. </description> </property> <property> <name>dfs.block.size</name> <value>131072</value> <description>Default block replication. The actual number of replications can be specified when the file is created. The default is used if replication is not specified in create time. </description> </property> </configuration> does these setting affects performance of hive? dfs.replication=3 dfs.block.size=131072 can i set it from hive prompt as hive>set dfs.replication=5 Is this value remains for a perticular session only ? or Is it better to change it in .xml file ?

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  • detect click on submit button in PHP

    - by Remus Rigo
    hi all I have a php file that contains a form (witch contains 2 input boxes and a submit button) for updating a contact. I managed to fill the fields with the contact's data, but I can't detect if the submit button is clicked form looks like this echo "<form action=Contact.php><table>". "<tr><td>First Name</td><td><input type=text size=75% name=FirstName value='".$row['FirstName']."'></td></tr>". "<tr><td>Last Name</td><td><input type=text size=75% name=LastName value='".$row['LastName']."'></td></tr>". "<tr><td colspan=2><input type=submit name=UpdateContact value=Update></td></tr>". "</table></form>"; this code should output a "clicked" message if the button is clicked if (isset($_POST['UpdateContact'])) { echo "<p>clicked"; } else { echo "<p>not clicked"; } can anyone help me out or tell me what i've done wrong (I want from the same php file to fill the contact's data in a from and to update the database)

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  • C++ Segmentation Fault when Iterating through a Vector

    - by user1790374
    I have a program that maintains an integer vector. I have three functions that add an integer, remove an integer and check whether an integer is already in the vector. The problem is with the last one. vector<int> children; void CtpTestingApplication::addChild(int child) { for (int i=0; i<children.size(); i++) { //already a child if (children[i]==child) return; } //child not yet recorded children.push_back(child); received.push_back(false); cout<<"added child "<<child; } void CtpTestingApplication::removeChild(int child) { Enter_Method("removeChild"); for (int i=0; i<children.size(); i++) { //already a child, remove it if (children[i]==child) { children.erase(children.begin()+i); received.erase(received.begin()+i); cout<<"removed child "<<child; } } //not recorded, no need to remove } bool CtpTestingApplication::isChild(int child) { Enter_Method("isChild"); vector<int>::iterator ic; bool result = false; for (ic= children.begin(); ic < children.end(); ic++) { cout<<*ic<<" vs "<<child; // if (child==*ic) result = true; } return result; } I always get segmentation fault when I uncomment "if (child==*ic)", even though printouts show that the vector is not empty and contains the expected integers. For example, with the if statements commented, I can see 1 vs 4, 2 vs 4, 4 vs 4, 12 vs 4 I also attempted looping using children[i] and so on, but to no avail. Any help would be appreciated. Thank you.

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  • How to algorithmically partion a keyspace?

    - by pbhogan
    This is related to consistent hashing and while I conceptually understand what I need to do, I'm having a hard time translating this into code. I'm trying to divide a given keyspace (say, 128 bits) into equal sized partitions. I want the upper bound (highest key) of each partition. Basically, how would I complete this? #define KEYSPACE_BYTE_SIZE 16 #define KEYSPACE_BIT_SIZE (KEYSPACE_BYTE_SIZE * 8) typedef struct _key { char byte[KEYSPACE_BYTE_SIZE]; } key; key * partition_keyspace( int num_partitions ) { key * partitions = malloc( sizeof(key) * num_partitions ); // ... }

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  • How to copy a structure with pointers to data inside (so to copy pointers and data they point to)?

    - by Kabumbus
    so I have a structure like struct GetResultStructure { int length; char* ptr; }; I need a way to make a full copy of it meaning I need a copy to have a structure with new ptr poinnting on to copy of data I had in original structure. Is It any how possible? I mean any structure I have which contains ptrs will have some fields with its lengths I need a function that would copy my structure coping all ptrs and data they point to by given array of lengthes... Any cool boost function for it? Or any way how to create such function?

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