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  • C++ template and pointers

    - by Kary
    I have a problem with a template and pointers ( I think ). Below is the part of my code: /* ItemCollection.h */ #ifndef ITEMCOLLECTION_H #define ITEMCOLLECTION_H #include <cstddef> using namespace std; template <class T> class ItemCollection { public: // constructor //destructor void insertItem( const T ); private: struct Item { T price; Item* left; Item* right; }; Item* root; Item* insert( T, Item* ); }; #endif And the file with function defintion: /* ItemCollectionTemp.h-member functions defintion */ #include <iostream> #include <cstddef> #include "ItemCollection.h" template <class Type> Item* ItemCollection <T>::insert( T p, Item* ptr) { // function body } Here are the errors which are generated by this line of code: Item* ItemCollection <T>::insert( T p, Item* ptr) Errors: error C2143: syntax error : missing ';' before '*' error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2065: 'Type' : undeclared identifier error C2065: 'Type' : undeclared identifier error C2146: syntax error : missing ')' before identifier 'p' error C4430: missing type specifier - int assumed. Note: C++ does not support default-int error C2470: 'ItemCollection::insert' : looks like a function definition, but there is no parameter list; skipping apparent body error C2072: 'ItemCollection::insert': initialization of a function error C2059: syntax error : ')' Any help is much appreciated.

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  • is there a simple timed lock algorithm avoiding deadlock on multiple mutexes?

    - by Vicente Botet Escriba
    C++0x thread library or Boost.thread define a non-member variadic template function that locks all mutex at once that helps to avoid deadlock. template <class L1, class L2, class... L3> void lock(L1&, L2&, L3&...); The same can be applied to a non-member variadic template function try_lock_until, which locks all the mutex until a given time is reached that helps to avoid deadlock like lock(...). template <class Clock, class Duration, class L1, class L2, class... L3> void try_lock_until( const chrono::time_point<Clock,Duration>& abs_time, L1&, L2&, L3&...); I have an implementation that follows the same design as the Boost function boost::lock(...). But this is quite complex. As I can be missing something evident I wanted to know if: is there a simple timed lock algorithm avoiding deadlock on multiple mutexes? If no simple implementation exists, can this justify a proposal to Boost? P.S. Please avoid posting complex solutions.

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  • Storing C++ templated objects as same type

    - by JaredC
    I have a class that is a core component of a performance sensitive code path, so I am trying to optimize it as much as possible. The class used to be: class Widget { Widget(int n) : N(n) {} .... member functions that use the constant value N .... const int N; // just initialized, will never change } The arguments to the constructor are known at compile time, so I have changed this class to a template, so that N can be compiled into the functions: template<int N> class Widget { .... member functions that use N .... } I have another class with a method: Widget & GetWidget(int index); However, after templating Widget, each widget has a different type so I cannot define the function like this anymore. I considered different inheritance options, but I'm not sure that the performance gain from the template would outweigh the cost of inherited function invocations. SO, my question is this: I am pretty sure I want the best of both worlds (compile-time / run-time), and it may not be possible. But, is there a way to gain the performance of knowing N at compile time, but still being able to return Widgets as the same type? Thanks!

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  • Why would 1.000 subforms in a db be a bad idea?

    - by KlaymenDK
    Warm-up I'm trying to come up with a good way to implement customized document forms. It's for a tool to request access to applications; each application will want to ask its own specific questions. The thing is, we have one kind of (common) user who needs to fill in and submit documents based on templates, and another kind of (super) user who needs to be able to define what each template needs to contain. One implementation option would be to use a form (with the basic mandatory stuff), and have that form dynamically include a subform appropriate to the specific task at hand. The gist of the matter is that we could (=will!) quite easily end up having many hundreds of different subforms! (NB. These subforms will be maintained in an automated manner, but that is another topic that may be considered outside the scope of this Question.) Question It's common knowledge that having a lot of views in a Notes database is Bad Thing. But has anyone tried pushing the number of forms or subforms and made any experiences regarding performance?

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  • opengl: question about glutMainLoop()

    - by lego69
    can somebody explain how does glutMainLoop work? and second question, why glClearColor(0.0f, 0.0f, 1.0f, 1.0f); defined after glutDisplayFunc(RenderScene); cause firstly we call glClear(GL_COLOR_BUFFER_BIT); and only then define glClearColor(0.0f, 0.0f, 1.0f, 1.0f); int main(int argc, char* argv[]) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutInitWindowSize(800, 00); glutInitWindowPosition(300,50); glutCreateWindow("GLRect"); glutDisplayFunc(RenderScene); glutReshapeFunc(ChangeSize); glClearColor(0.0f, 0.0f, 1.0f, 1.0f); <-- glutMainLoop(); return 0; } void RenderScene(void) { // Clear the window with current clearing color glClear(GL_COLOR_BUFFER_BIT); // Set current drawing color to red // R G B glColor3f(1.0f, 0.0f, 1.0f); // Draw a filled rectangle with current color glRectf(0.0f, 0.0f, 50.0f, -50.0f); // Flush drawing commands glFlush(); }

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  • Discussion - Allowing / blocking user access to pages / Client Side Validation (Client Side Only!) -

    - by Ozaki
    TLDR Using plain HTML / Javascript (Client Side) I want to prevent viewing of certain pages. The user will have to type a username and password and depending on that they get access to different pages. Answers can NOT include server side whatsoever It does not matter if they can break it easily. There is no sensitive information etc. Also the target audience will not have access to internet OR probably know what a cookie is... At some point the user will have to type username / password.(I can define the cookie here) Currently I thought of using cookies to set a cookie for each page to say "true" / "false" but that would get messy with so many cookies. Or setting an array within a cookie for each page? I have div field "#Content" which as it looks encompasses all of my content on the page so blocking out content will be as simple as replacing it with ("sorry you don't have access") etc. For Example: $.cookie("Access","page1, page2, page3"{ expires: 1 }); I am looking for anyway to do this does not have to be with cookies. Would be nice to get a discussion of different ways this can be done. So the question is: What do YOU think would be a good way to go about doing this with client side validation? Also on another note discussion on how to make client side more secure or ways to do so are acceptable.

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  • Error "initializer element is not constant" when trying to initialize variable with const

    - by tomlogic
    I get an error on line 6 (initialize my_foo to foo_init) of the following program and I'm not sure I understand why. typedef struct foo_t { int a, b, c; } foo_t; const foo_t foo_init = { 1, 2, 3 }; foo_t my_foo = foo_init; int main() { return 0; } Keep in mind this is a simplified version of a larger, multi-file project I'm working on. The goal was to have a single constant in the object file, that multiple files could use to initialize a state structure. Since it's an embedded target with limited resources and the struct isn't that small, I don't want multiple copies of the source. I'd prefer not to use: #define foo_init { 1, 2, 3 } I'm also trying to write portable code, so I need a solution that's valid C89 or C99. Does this have to do with the ORGs in an object file? That initialized variables go into one ORG and are initialized by copying the contents of a second ORG? Maybe I'll just need to change my tactic, and have an initializing function do all of the copies at startup. Unless there are other ideas out there?

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  • Determining presence of prototype with correct return type

    - by R..
    Here's a random problem in C black magic I just came up with: Write a function that returns 1 if malloc has been prototyped to return a pointer type and 0 if malloc has a return type of int (either implicitly or due to wrong prototype), without invoking any implementation-defined or undefined behavior. I believe it's solvable, but I haven't worked out the solution. Note that calling the function cannot be necessary and in fact is not possible since calling a function with the incorrect prototype is undefined behavior. I have some ideas for ingredients but I think it makes for a better puzzle (and possibly more diverse ideas) if I leave them out for now. I don't need the solution for any immediate use, but it could be handy in configure scripts and such. Update: A better example of the usefulness (with strdup instead of malloc): #undef strdup #define strdup(x) (strdup_has_proto ? strdup((x)) : my_strdup((x))) i.e. being able to implement X_has_proto as an expression at the source level could be a portable way to use functions which a system might or might not have, and fall back on a local replacement, without needing any separate configure step.

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  • C++, overloading std::swap, compiler error, VS 2010

    - by Ian
    I would like to overload std::swap in my template class. In the following code (simplified) #ifndef Point2D_H #define Point2D_H template <class T> class Point2D { protected: T x; T y; public: Point2D () : x ( 0 ), y ( 0 ) {} Point2D( const T &x_, const T &y_ ) : x ( x_ ), y ( y_ ) {} .... public: void swap ( Point2D <T> &p ); }; template <class T> inline void swap ( Point2D <T> &p1, Point2D <T> &p2 ) { p1.swap ( p2 ); } namespace std { template <class T> inline void swap ( Point2D <T> &p1, Point2D <T> &p2 ) { p1.swap ( p2 ); } } template <class T> void Point2D <T>::swap ( Point2D <T> &p ) { using (std::swap); swap ( x, p.x ); swap ( y, p.y ); } #endif there is a compiler error (only in VS 2010): error C2668: 'std::swap' : ambiguous call to overloaded I do not know why, std::swap should be overoaded... Using g ++ code works perfectly. Without templates (i.e. Point2D is not a template class) this code also works.. Thanks for your help.

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  • Format a timestamp into text

    - by user1257114
    I want to get the Modify date of a file and then format it into a human readable date. I am running a C program that gets information on when a particular file was last modified. My C Code contains a sytem cmd which contains a number of egreps, awks, seds separated by pipes. Using sed or awk or something similar, how can I convert 06 to June (This can be any month so an array or something is required) What I am trying to achieve is to end up with a string similar to: My C code contains: char string1[100] = ""; #define MAXCHAR 100 FILE *fp; char str[MAXCHAR], str2[MAXCHAR]; char* filename = "newfile"; /* stat: run 'stat' on the dtlName file to display status information. egrep: search for the pattern 'Modify' and print the lines containing it. awk: Get columns 2 & 3 sed: replace the . with a space, leaving 3 columns of output awk: only print cols 1 & 2 to newfile sed: replace '-' with ' ' in newfile awk: format output in newfile */ sprintf(string1, "/bin/stat %s \ | egrep Modify \ | /bin/awk '{print $2, $3}' \ | /bin/sed 's/\\./ /g' \ | /bin/awk '{print $1, $2}' \ | /bin/sed 's/-/ /g' \ | /bin/awk '{print $3,$2\", \"$1,\"at\",$4}' > newfile" , dtlName); system(string1); fp = fopen(filename, "r"); while (fgets(str, MAXCHAR, fp) != NULL) sprintf(str2,"%s", str); /* Write information to file */ DisplayReportFile (report); ReportEntry (report,L"Source file: %s, Created: %s\n\n",dtlName,str2);

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  • Google maps api Directions User defined Steps

    - by Via Lactea
    Hi All, I have a google map service with the stores mapped on it. I also have directions service (then you define two addresses or more and it shows you a way on this map, see google map api directions). So I wa?? to show the nearest stores to this way. Of course it could be the store located in the next streat of my way, so it also should be included to the list. So far I just found only an array of steps in the directions object which I get from google maps api. But these steps are predefined by google, so they can be too close one each to other and they also can be too far (if a part of your route is a highway or there is no any special steps on your way etc.) So, what I want to do. I want to make my own steps on the line that I get from google directions (for example to put these steps on my line every 500 meeters etc.), and after that to search every step for any stores around 200 meeters. Is it possible to do? I cannot find any solution of this idea in internet.

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  • Parsing string based on initial format

    - by Kayla
    I'm trying to parse a set of lines and extract certain parts of the string based on an initial format (reading a configuration file). A little more explanation: the format can contain up to 4 parts to be formatted. This case, %S will skip the part, %a-%c will extract the part and will be treated as a string, %d as int. What I am trying to do now is to come up with some clever way to parse it. So far I came up with the following prototype. However, my pointer arithmetic still needs some work to skip/extract the parts. Ultimately each part will be stored on an array of structs. Such as: struct st_temp { char *parta; char *partb; char *partc; char *partd; }; ... #include <stdio.h> #include <string.h> #define DIM(x) (sizeof(x)/sizeof(*(x))) void process (const char *fmt, const char *line) { char c; const char *src = fmt; while ((c = *src++) != '\0') { if (c == 'S'); // skip part else if (c == 'a'); // extract %a else if (c == 'b'); // extract %b else if (c == 'c'); // extract %c else if (c == 'd'); // extract %d (int) else { printf("Unknown format\n"); exit(1); } } } static const char *input[] = { "bar 200.1 / / (zaz) - \"bon 10\"", "foo 100.1 / / (baz) - \"apt 20\"", }; int main (void) { const char *fmt = "%S %a / / (%b) - \"%c %d\""; size_t i; for(i = 0; i < DIM (input); i++) { process (fmt, input[i]); } return (0); }

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  • C# language questions

    - by Water Cooler v2
    1) What is int? Is it any different from the struct System.Int32? I understand that the former is a C# alias (typedef or #define equivalant) for the CLR type System.Int32. Is this understanding correct? 2) When we say: IComparable x = 10; Is that like saying: IComparable x = new System.Int32(); But we can't new a struct, right? or in C like syntax: struct System.In32 *x; x=>someThing = 10; 3) What is String with a capitalized S? I see in Reflector that it is the sealed String class, which, of course, is a reference type, unlike the System.Int32 above, which is a value type. What is string, with an uncapitalized s, though? Is that also the C# alias for this class? Why can I not see the alias definitions in Reflector? 4) Try to follow me down this subtle train of thought, if you please. We know that a storage location of a particular type can only access properties and members on its interface. That means: Person p = new Customer(); p.Name = "Water Cooler v2"; // legal because as Name is defined on Person. but // illegal without an explicit cast even though the backing // store is a Customer, the storage location is of type // Person, which doesn't support the member/method being // accessed/called. p.GetTotalValueOfOrdersMade(); Now, with that inference, consider this scenario: int i = 10; // obvious System.object defines no member to // store an integer value or any other value in. // So, my question really is, when the integer is // boxed, what is the *type* it is actually boxed to. // In other words, what is the type that forms the // backing store on the heap, for this operation? object x = i;

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  • How can we find second maximum from array efficiently?

    - by Xinus
    Is it possible to find the second maximum number from an array of integers by traversing the array only once? As an example, I have a array of five integers from which I want to find second maximum number. Here is an attempt I gave in the interview: #define MIN -1 int main() { int max=MIN,second_max=MIN; int arr[6]={0,1,2,3,4,5}; for(int i=0;i<5;i++){ cout<<"::"<<arr[i]; } for(int i=0;i<5;i++){ if(arr[i]>max){ second_max=max; max=arr[i]; } } cout<<endl<<"Second Max:"<<second_max; int i; cin>>i; return 0; } The interviewer, however, came up with the test case int arr[6]={5,4,3,2,1,0};, which prevents it from going to the if condition the second time. I said to the interviewer that the only way would be to parse the array two times (two for loops). Does anybody have a better solution?

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  • Plugin architecture in C using libdl

    - by LukeN
    I've been toying around, writing a small IRC framework in C that I'm now going to expand with some core functionality - but beyond that, I'd like it to be extensible with plugins! Up until now, whenever I wrote something IRC related (and I wrote a lot, in about 6 different languages now... I'm on fire!) and actually went ahead to implement a plugin architecture, it was inside an interpreted language that had facilities for doing (read: abusing) so, like jamming a whole script file trough eval in Ruby (bad!). Now I want to abuse something in C! Basically there's three things I could do define a simple script language inside of my program use an existing one, embedding an interpreter use libdl to load *.so modules on runtime I'm fond of the third one and raather avoid the other two options if possible. Maybe I'm a masochist of some sort, but I think it could be both fun and useful for learning purposes. Logically thinking, the obvious "pain-chain" would be (lowest to highest) 2 - 1 - 3, for the simple reason that libdl is dealing with raw code that can (and will) explode in my face more often than not. So this question goes out to you, fellow users of stackoverflow, do you think libdl is up to this task, or even a realistic thought?

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  • Is there an user-level accessible font table present in Linux?

    - by youngdood
    Hi again Stackoverflow! Since there is this: http://en.wikipedia.org/wiki/Code_page_437 For MSDOS, is there something similar for Linux systems? Is it possible to access that font data via userland program? I would actually just need an access to the actual bit patterns which define the font, and I would do the rendering myself. I'm fairly sure that something like this exists, but I haven't been able to find what exactly is it and how to access it. After all, e.g. text mode console font has to reside somewhere, and I really do hope it is "rawly" accessible somehow for a userland program. Before I forget, I'm programming my program in C, and have access only to the "standard" linux/posix development headers. The only thing I could came up with myself is to use the fonts in /usr/share/fonts, but having to write my own implementations to extract the data from there doesn't sound really an option; I would really want to achieve this with the least amount of bytes possible, so I feel I'm left with finding a standard way of doing this. It's not really feasible for me to store my own 8x8 ASCII-compatible font with the program either(it takes some 1024 bytes(128 chars * 8x8 bits) just to store the font, which is definitely unacceptable for the strict size limits(some < 1024 bytes for code+data) which I am working with), so being able to use the font data stored at the system itself would greatly simplify my task.

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  • Is the 'var' keyword bad? Or am I just old school?

    - by WaggingSiberian
    Recently I overheard junior developer ask "why do you use 'var' so much?". The mid-level developer responded "I use VAR all the time. I love it! I don't have to figure out the type." I didn't have the time or energy to get into a religious war and hey, I'm still the new guy here :-) I understand var has its place. LINQ comes to mind. But I have also always been told the use of var represents lazy programming and I should just use the correct type to begin with. If it's an int, define it as an int, not a var. When reviewing code, seeing the type makes it easier to follow. My opinion is, it's just lazy but there are exceptions. Var also reminds me of the VB/VBA variant type. It also had its place. I recall (from many years ago) its usage being less-than-desirable type and it was rather resource hungry. Am I just being stuck in my ways? Should we start using var all the time as my co-worker does?

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  • How can I dynamically call the named route in a :partial in rails?

    - by Angela
    I have the following partial. It can be called from three different times in a view as follows: <%= render :partial => "contact_event", :collection => @contacts, :locals => {:event => email} %> Second time: <%= render :partial => "contact_event", :collection => @contacts, :locals => {:event => call} %> Third time: <%= render :partial => "contact_event", :collection => @contacts, :locals => {:event => letter} %> In each instance, call, email, letter refer to a specific instance of a Model Call, Email, or Letter. Here is what I tried to do and conceptually what I'd like to do: assign the route based on the class name that has been passed to the :event from the :partial. What I did was create what the actual url should be. The 'text' of it is correct, but doesn't seem to recognize it as a named route. <% url = "skip_contact_#{event.class.name.tableize.singularize}_url" % <%= link_to_remote "Skip #{url} Remote", :url = skip_contact_email_url(contact_event, event), :update = "update-area-#{contact_event.id}-#{event.id}" % ' My challenge: skip_contact_email_url only works when the event refers to an email. How can I dynamically define skip_contact_email_url to be skip_contact_letter_url if the local variable is letter? Even better, how can I have a single named route that would do the appropriate action?

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  • Parser Error Problem

    - by user177140
    Hi I have found a problem in Multilingual Asp.Net Web Application I have Created a Global.asax file and write the code private void Application_BeginRequest(Object source, EventArgs e) { string[] languages = HttpContext.Current.Request.UserLanguages; if (languages[0].ToLower() != null && languages[0].ToLower()!="") { System.Threading.Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo(languages[0].ToLower()); System.Threading.Thread.CurrentThread.CurrentCulture = System.Globalization.CultureInfo.CreateSpecificCulture(languages[0].ToLower()); } } and define Label Like this <asp:Label ID="Labeldg" runat="server" Text="<%$ Resources:Resource, Labeldg %>"</asp:Label> But it through Parser error like: Parser Error Description: An error occurred during the parsing of a resource required to service this request. Please review the following specific parse error details and modify your source file appropriately. Parser Error Message: The resource object with key 'LblUsrName_Login' was not found. Source Error: </div> <div class="impcLoginText_Login"> <asp:Label ID="LblUsrName" runat="server" Text="<%$ Resources:PageResource, LblUsrName_Login %>" "></asp:Label>

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  • What is the most obfuscated and clever code you've seen? [closed]

    - by ThibThib
    I am aware about the The International Obfuscated C Code Contest, but I am looking for obfuscated AND clever codes (specially short ones) Here is two examples (the first one is a classical one, I think) #define _ F-->00 || F-OO--; long F=00,OO=00; main(){F_OO();printf("%1.3f\n", 4.*-F/OO/OO);}F_OO() { _-_-_-_ _-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_-_-_-_ _-_-_-_-_-_-_-_-_ _-_-_-_ } and #include <unistd.h> float o=0.075,h=1.5,T,r,O,l,I;int _,L=80,s=3200;main(){for(;s%L|| (h-=o,T= -2),s;4 -(r=O*O)<(l=I*I)|++ _==L&&write(1,(--s%L?_<L?--_ %6:6:7)+"World! \n",1)&&(O=I=l=_=r=0,T+=o /2))O=I*2*O+h,I=l+T-r;} I let you compile and run them so as to understand what they are producing. Of course, I am not looking for only obfuscated code, because I guess that every code could be transformed in a way that it is not readable at all I am more looking for small codes that you can eventually understand, with some clever tricks. I will show them to my students as example of clever things that they should not do (it's always better to show clever examples rather than stupid ones...) Thanks

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  • C++ traits question

    - by duli
    I have a templated class template <typename Data> class C { ..... } In most situations, I depend on the compiler to let me substitute types for Data. I call methods foo(), goo() on objects of type Data, so what I substitute needs to provide that. I now need to substitute int and string for my Data type. I do not want to specialize because the class is already too big and would require specializing each method (with only small code change). My options (please tell me if there are more) 1) I can provide wrapper classes around int and string which implement the methods foo(), goo() etc 2) provide a traits class traits that calls foo() or goo() on objects of classes that provide foo(),goo() (these are my present substitutable classes) and specialize these classes for int and string. Questions 1) what are the relative merits of 1 vs 2? 2) My traits classes will have static methods. Can a traits class have non-static methods as well? I see most traits classes define constants in the STL. 3) Do I make the traits classes global or should I pass them in as a template parameter for class C?

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  • Saving a Record with Rails Association

    - by tshauck
    Hi, I've been going through the Rails Guides, but have gotten stuck on associations after going through validations and migrations. So, I have the following models Job and Person, where a Person can have many jobs. I know that in reality there'd be a many-to-many, but I'm trying to get my handle on this first. class Job < ActiveRecord::Base belongs_to :people end and class Person < ActiveRecord::Base has_many :jobs end Here's the schema ActiveRecord::Schema.define(:version => 20110108185924) do create_table "jobs", :force => true do |t| t.string "occupation" t.boolean "like" t.datetime "created_at" t.datetime "updated_at" t.integer "person_id" end create_table "people", :force => true do |t| t.string "first_name" t.string "last_name" t.datetime "created_at" t.datetime "updated_at" end end Is there some I can do the following j = Job.first; j.Person? Then that'd give me access to the Person object associated with the j. I couldn't find it on guides.rubyonrails.org, although it has been very helpful getting a grip on migrations and validations thus far. Thanks PS, If there are any tutorials that covers more of this kind of things links would be great.

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  • C# property exactly the same, defined in two places

    - by Sarah Vessels
    I have the following classes: Defect - represents a type of data that can be found in a database FilterQuery - provides a way of querying the database by setting simple Boolean filters Both Defect and FilterQuery implement the same interface: IDefectProperties. This interface specifies particular fields that are in the database. Different classes have methods that return lists of Defect instances. With FilterQuery, you specify some filters for the particular properties implemented as part of IDefectProperties, and then you run the query and get back a list of Defect instances. My problem is that I end up implementing some properties exactly the same in FilterQuery and Defect. The two are inherently different classes, they just share some of the same properties. For example: public DateTime SubmitDateAsDate { get { return DateTime.Parse(SubmitDate); } set { SubmitDate = value.ToString(); } } This is a property required by IDefectProperties that depends on a different property, SubmitDate, which returns a string instead of a DateTime. Now SubmitDate is implemented differently in Defect and FilterQuery, but SubmitDateAsDate is exactly the same. Is there a way that I can define SubmitDateAsDate in only place, but both Defect and FilterQuery provide it as a property? FilterQuery and Defect already inherit from two different classes, and it wouldn't make sense for them to share an ancestor anyway, I think. I am open to suggestions as to my design here as well.

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  • Operator+ for a subtype of a template class.

    - by baol
    I have a template class that defines a subtype. I'm trying to define the binary operator+ as a template function, but the compiler cannot resolve the template version of the operator+. #include <iostream> template<typename other_type> struct c { c(other_type v) : cs(v) {} struct subtype { subtype(other_type v) : val(v) {} other_type val; } cs; }; template<typename other_type> typename c<other_type>::subtype operator+(const typename c<other_type>::subtype& left, const typename c<other_type>::subtype& right) { return typename c<other_type>::subtype(left.val + right.val); } // This one works // c<int>::subtype operator+(const c<int>::subtype& left, // const c<int>::subtype& right) // { return c<int>::subtype(left.val + right.val); } int main() { c<int> c1 = 1; c<int> c2 = 2; c<int>::subtype cs3 = c1.cs + c2.cs; std::cerr << cs3.val << std::endl; } I think the reason is because the compiler (g++4.3) cannot guess the template type so it's searching for operator+<int> instead of operator+. What's the reason for that? What elegant solution can you suggest?

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  • Is `super` local variable?

    - by Michael
    // A : Parent @implementation A -(id) init { // change self here then return it } @end A A *a = [[A alloc] init]; a. Just wondering, if self is a local variable or global? If it's local then what is the point of self = [super init] in init? I can successfully define some local variable and use like this, why would I need to assign it to self. -(id) init { id tmp = [super init]; if(tmp != nil) { //do stuff } return tmp; } b. If [super init] returns some other object instance and I have to overwrite self then I will not be able to access A's methods any more, since it will be completely new object? Am I right? c. super and self pointing to the same memory and the major difference between them is method lookup order. Am I right? sorry, don't have Mac to try, learning theory as for now...

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