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  • Java Variable Initialization

    - by Samuel Brainard
    Here's a piece of code I wrote. public class cube { private int length; private int breadth; private int height; private int volume; private int density; private int weight; public cube(int l,int b,int h, int d) { length=l; breadth=b; height=h; density=d; } public void volmeShow(){ volume=length*breadth*height; System.out.println("The Volume of the cube is "+this.volume); So if I implement the above cube class like this, public class cubeApp { public static void main(String[] args){ cube mycube = new cube(5,6,9,2); mycube.volumeShow(); I get an output that tells me Volume is 270. But I get an output that says Volume is 0 if I define the volume variable like this: public class cube { private int length; private int breadth; private int height; private int volume=length*breadth*height; private int density; private int weight; public cube(int l,int b,int h, int d) { length=l; breadth=b; height=h; density=d; } public void volmeShow(){ System.out.println("The Volume of the cube is "+this.volume); Can somebody please explain why this is happening? Thanks, Samuel.

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  • I can't get that `bus error` to stop sucking.

    - by Koning Baard XIV
    I have this a class called PPString: PPString.h #ifndef __CPP_PPString #define __CPP_PPString #include "PPObject.h" class PPString : public PPObject { char *stringValue[]; public: char *pointerToCharString(); void setCharString(char *charString[]); void setCharString(const char charString[]); }; #endif PPString.cpp #include "PPString.h" char *PPString::pointerToCharString() { return *stringValue; } void PPString::setCharString(char *charString[]) { *stringValue = *charString; } void PPString::setCharString(const char charString[]) { *stringValue = (char *)charString; } I'm trying to set the stringValue using std::cin: main.cpp PPString myString; myString.setCharString("LOLZ"); std::cout << myString.pointerToCharString() << std::endl; char *aa[1000]; std::cin >> *aa; myString.setCharString(aa); std::cout << myString.pointerToCharString() << std::endl; The first one, which uses a const char works, but the second one, with a char doesn't, and I get this output: copy and paste from STDOUT LOLZ im entering a string now... Bus error where the second line is what I entered, followed by pressing the return key. Can anyone help me fixing this? Thanks...

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  • Dynamic change .click value Jquery IE issue.

    - by user326100
    Hello guys.. it's i first time i'm asking here. Sorry if the answer is available already. I have a very small jQuery script that canges the paramether for onclick attr on a DIV. IT works like as right and left arrows for some content in the middle. BAsically i set the onclick="foo(1)" then when get clicked sld change the value 1 to 2, and keep changing everytime i click. on jQuery functio i'm using: $("#v_arrow_r").attr('onclick','').unbind().click(newclick_next); it works like a charm on FF and Chrome, but does not work on IE !!!! Argh... here the the code: if (start == 24) { var a = 0; var b = 0; } else { var a = start-6; var b = start+6; } next = "home_featured_videos(" + b + ");"; newclick_next = eval("(function(){"+next+"});"); prev = "home_featured_videos(" + a + ");"; newclick_prev = eval("(function(){"+prev+"});"); $('#video-module').css('background',''); $('#video-module').html(response); $("#v_arrow_l").attr('onclick','').unbind().click(newclick_prev); $("#v_arrow_r").attr('onclick','').unbind().click(newclick_next); The html: //CONTENT So like i said.. i define the attr onclick when page open. It work well on IE. but when i click the arrow and call the function the oncli is set to null and i add the function to .click. IE stop working. the click is dead. If anybody have idea why this is happening. Thanx in advance. Kind Regards Varois

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  • Textbox extends outside of the grid cell in .Net 4.0 (but not in 3.5)

    - by Bryant
    There seems to be a change in behaviour between .Net 3.5 and .Net 4.0. If I define a window as: <Window x:Class="WpfApplication1.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="350" Width="500" > <Grid> <Grid.ColumnDefinitions> <ColumnDefinition MinWidth="300" /> <ColumnDefinition /> </Grid.ColumnDefinitions> <TextBox Grid.Column="1" ScrollViewer.CanContentScroll="True" ScrollViewer.HorizontalScrollBarVisibility="Auto" Text="abc abc abc abc abc abc abc abc abcabc abc abcabc abc abc abc abc abc" /> </Grid> </Window> In .Net 3.5 the textbox correctly contains itself within the grid cell but in .Net 4.0 it extends beyond the cell and so gets clipped. This only happens if the MinWidth of the first column is greater than 50% of the overall width. Does anyone know how to get 4.0 to exhibit the same behavior as 3.5?

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  • Ruby & ActiveRecord: referring to integer fields by (uniquely mapped) strings

    - by JP
    While its not my application a simple way to explain my problem is to assume I'm running a URL shortener. Rather than attempt to try and figure out what the next string I should use as the unique section of the URL, I just index all my URLs by integer and map the numbers to strings behind the scenes, essentially just changing the base of the number to, let's say, 62: a-z + A-Z + 0-9. In ActiveRecord I can easily alter the reader for the url_id field so that it returns my base 62 string instead of the number being stored in the database: class Short < ActiveRecord::Base def url_id i = read_attribute(:convo) return '0' if i == 0 s = '' while i > 0 s << CHARS[i.modulo(62)] i /= 62 end s end end but is there a way to tell ActiveRecord to accept Short.find(:first,:conditions=>{:url_id=>'Ab7'}), ie. putting the 'decoding' logic into my Short ActiveRecord class? I guess I could define my own def self.find_by_unique_string(string), but that feels like cheating somehow! Thanks!

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  • [C++] Trouble declaring and recognizing global functions

    - by Sarah
    I've created some mathematical functions that will be used in main() and by member functions in multiple host classes. I was thinking it would be easiest to make these math functions global in scope, but I'm not sure how to do this. I've currently put all the functions in a file called Rdraws.cpp, with the prototypes in Rdraws.h. Even with all the #includes and externs, I'm getting a "symbol not found" error at the first function call in main(). Here's what I have: // Rdraws.cpp #include <cstdlib> using namespace std; #include <cmath> #include "Rdraws.h" #include "rng.h" extern RNG rgen // this is the PRNG used in the simulation; global scope void rmultinom( double p_trans[], int numTrials, int numTrans, int numEachTrans[] ) { // function 1 def } void rmultinom( const double p_trans[], const int numTrials, int numTrans, int numEachTrans[]) { // function 2 def } int rbinom( int nTrials, double pLeaving ) { // function 3 def } // Rdraws.h #ifndef RDRAWS #define RDRAWS void rmultinom( double[], int, int, int[] ); void rmultinom( const double[], const int, int, int[] ); int rbinom( int, double ); #endif // main.cpp ... #include "Rdraws.h" ... extern void rmultinom(double p_trans[], int numTrials, int numTrans, int numEachTrans[]); extern void rmultinom(const double p_trans[], const int numTrials, int numTrans, int numEachTrans[]); extern int rbinom( int n, double p ); ... int main() { ... } I'm pretty new to programming. If there's a dramatically smarter way to do this, I'd love to know.

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  • GetLongPathName Undeclared

    - by iwizardpro
    When I try to compile my code with the function GetLongPathName(), the compiler tells me that the function is undeclared. I have already read the MSDN documentation located @ http://msdn.microsoft.com/en-us/library/aa364980%28VS.85%29.aspx. But, even though I included those header files, I am still getting the undeclared function error. Which header file(s) am I supposed to include when using the function? #include <Windows.h> #include <WinBase.h> #define DLLEXPORT extern "C" __declspec(dllexport) DLLEXPORT char* file_get_long(char* path_original) { long length = 0; TCHAR* buffer = NULL; if(!path_original) { return "-10"; } length = GetLongPathName(path_original, NULL, 0); if(length == 0) { return "-10"; } buffer = new TCHAR[length]; length = GetLongPathName(path_original, buffer, length); if(length == 0) { return "-10"; } return buffer; } And, if it makes a difference, I am currently compiling using Dev-C++ on a Windows Vista 64-bit.

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  • how to solve a weired swig python c++ interfacing type error

    - by user2981648
    I want to use swig to switch a simple cpp function to python and use "scipy.integrate.quadrature" function to calculate the integration. But python 2.7 reports a type error. Do you guys know what is going on here? Thanks a lot. Furthermore, "scipy.integrate.quad" runs smoothly. So is there something special for "scipy.integrate.quadrature" function? The code is in the following: File "testfunctions.h": #ifndef TESTFUNCTIONS_H #define TESTFUNCTIONS_H double test_square(double x); #endif File "testfunctions.cpp": #include "testfunctions.h" double test_square(double x) { return x * x; } File "swig_test.i" : /* File : swig_test.i */ %module swig_test %{ #include "testfunctions.h" %} /* Let's just grab the original header file here */ %include "testfunctions.h" File "test.py": import scipy.integrate import _swig_test print scipy.integrate.quadrature(_swig_test.test_square, 0., 1.) error info: UMD has deleted: _swig_test Traceback (most recent call last): File "<stdin>", line 1, in <module> File "C:\Python27\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 523, in runfile execfile(filename, namespace) File "D:\data\haitaliu\Desktop\Projects\swig_test\Release\test.py", line 4, in <module> print scipy.integrate.quadrature(_swig_test.test_square, 0., 1.) File "C:\Python27\lib\site-packages\scipy\integrate\quadrature.py", line 161, in quadrature newval = fixed_quad(vfunc, a, b, (), n)[0] File "C:\Python27\lib\site-packages\scipy\integrate\quadrature.py", line 61, in fixed_quad return (b-a)/2.0*sum(w*func(y,*args),0), None File "C:\Python27\lib\site-packages\scipy\integrate\quadrature.py", line 90, in vfunc return func(x, *args) TypeError: in method 'test_square', argument 1 of type 'double'

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  • (How) Can I approximate a "dynamic" index (key extractor) for Boost MultiIndex?

    - by Sarah
    I have a MultiIndex container of boost::shared_ptrs to members of class Host. These members contain private arrays bool infections[NUM_SEROTYPES] revealing Hosts' infection statuses with respect to each of 1,...,NUM_SEROTYPES serotypes. I want to be able to determine at any time in the simulation the number of people infected with a given serotype, but I'm not sure how: Ideally, Boost MultiIndex would allow me to sort, for example, by Host::isInfected( int s ), where s is the serotype of interest. From what I understand, MultiIndex key extractors aren't allowed to take arguments. An alternative would be to define an index for each serotype, but I don't see how to write the MultiIndex container typedef ... in such an extensible way. I will be changing the number of serotypes between simulations. (Do experienced programmers think this should be possible? I'll attempt it if so.) There are 2^(NUM_SEROTYPES) possible infection statuses. For small numbers of serotypes, I could use a single index based on this number (or a binary string) and come up with some mapping from this key to actual infection status. Counting is still darn slow. I could maintain a separate structure counting the total numbers of infecteds with each serotype. The synchrony is a bit of a pain, but the memory is fine. I would prefer a slicker option, since I would like to do further sorts on other host attributes (e.g., after counting the number infected with serotype s, count the number of those infected who are also in a particular household and have a particular age). Thanks in advance.

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  • Provider not notified from cookbook_file

    - by wittyhandle
    I'm working on an ssl provider using Vagrant (1.0.5) and chef-solo (10.12.0) I have my provider, called ssl within a cookbook called gtm_cq, I define it as such in my cookbook's default recipe: gtm_cq_ssl "author" do # attributes will come later end I then have my cookbook_file like below that should notify my ssl provider's import action once it pushes the cert up to the server: cookbook_file "#{node[:cq][:ssl][:author_cert_location]}/foo.cer" do source "foo.cer" owner "crx" group "root" mode "0644" notifies :import, resources(:gtm_cq_ssl => "author") end When I run this, the foo.cer gets pushed up as expected, but the import action of my ssl provider is never called. The most I see of any reference is these couple of lines in the log (removed log headers): .. cookbook_file[/opt/cq5/author/foo.cer] sending import action to gtm_cq_ssl[author] (delayed) .. Processing gtm_cq_ssl[author] action import (gtm_cq::author line 34) There's a large very obvious log statement as well as the use of another cookbook_file for a test file to push something up to the server. No log statement, no test file pushed. I'm certain too that the foo.cer file is removed from the server before each test. I found that if I edit my notifies line like so with :immediately notifies :import, resources(:gtm_cq_ssl => "author"), :immediately It seems to work. And I suppose this is ok in my particular case, but it would seem something is not right if that's the only way I can call my provider. Any help on this would be greatly appreciated. Thanks!

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  • Java / Spring MVC 3 validation of an email address

    - by Tim
    I have a Java backend with Spring MVC and I am using validation in this way on my domain object for an email address: import javax.validation.constraints.NotNull; import javax.validation.constraints.Pattern; import javax.validation.constraints.Size; ... @NotNull @Size(min = 1, max = 100) @Pattern(regexp="^([a-zA-Z0-9\\-\\.\\_]+)'+'(\\@)([a-zA-Z0-9\\-\\.]+)'+'(\\.)([a-zA-Z]{2,4})$") private String email; But all I get with these lines of code Set<ConstraintViolation<Person>> failures = validator.validate(personObject); ... Map<String, String> failureMessages = new HashMap<String, String>(); for (ConstraintViolation<Person> failure : failures) { failureMessages.put(failure.getPropertyPath().toString(), failure.getMessage()); System.out.println(failure.getPropertyPath().toString()+" - "+failure.getMessage()) } I get this on the console: email - must match "^([a-zA-Z0-9\\-\\.\\_]+)'+'(\\@)([a-zA-Z0-9\\-\\.]+)'+'(\\.)([a-zA-Z]{2,4})$" but I have as email address [email protected], so the regexp does not match. So I have two prolems: What's wrong here? And how can I define a error message on my own, because display this to the user, that is not a good thing :-) Thank you in advance for your help and Best Regards.

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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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  • Can I pass a non-generic type where a generic type is expected?

    - by Water Cooler v2
    I want to define a set of classes that collect and persist data. I want to call them either on-demand basis, or in a chain-of-responsibility fashion, as the caller pleases. To support the chaining, I have declared my interface like so: interface IDataManager<T, K> { T GetData(K args); void WriteData(Stream stream); void WriteData(T data, Stream stream); IDataCollectionPolicy Policy; IDataManager<T, K> NextDataManager; } But the T's and K's for each concrete types will be different. If I give it like this: IDataManager<T, K> NextDataManager; I assume that the calling code will only be able to chain types that have the same T's and K's. Is there a way I can have it chain any type of IDataManager? One thing that occurs to me is to have IDataManager inherit from a non-generic IDataManager like so: interface IDataManager { } interface IDataManager<T, K>: IDataManager { T GetData(K args); void WriteData(Stream stream); void WriteData(T data, Stream stream); IDataCollectionPolicy Policy; IDataManager NextDataManager; } Is this going to work?

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  • Using pair in c++

    - by user1543957
    Can someone please tell why i am unable to compile the following program #include<iostream> #include<string> #include<cmath> #include<iostream> #include<cfloat> #define MOD 10000009 using namespace std; double distance(pair<int,int> p1,pair<int,int> p2) { double dist; dist = sqrt( (p1.first-p2.first)*(p1.first-p2.first) + (p1.second-p2.second)*(p1.second-p2.second) ); return(dist); } int main() { int N,i,j; cin >> N; pair<int,int> pi[N]; for(i=0;i<N;i++) { cin >> pi[i].first >> pi[i].second; } for(i=0;i<N;i++) { cout << pi[i].first << " "<< pi[i].second << endl; } distance(pi[0],pi[1]); // This line is giving error return 0; }

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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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  • C++ Vector of vectors is messing with me

    - by xbonez
    If I put this code in a .cpp file and run it, it runs just fine: #include <iostream> #include <vector> #include <string> using namespace std; typedef vector<int> row; typedef vector<row> myMatrix; void main() { //cout << endl << "test" << endl; myMatrix mat(2,2); mat[0][1] = 2; cout << endl << mat[0][1] << endl; } But, if I make a .h and a .cpp file with the .h file like this, it gives me boatloads of errors. #ifndef _grid_ #define _grid_ #include<iostream> #include<vector> #include<string> using namespace std; typedef vector<int> row; typedef vector<row> myMatrix; class grid { public: grid(); ~grid(); int getElement(unsigned int ri, unsigned int ci); bool setElement(unsigned int ri, unsigned int ci, unsigned int value); private: myMatrix sudoku_(9,9); }; #endif These are some of the errors I get: warning C4091: 'typedef ' : ignored on left of 'int' when no variable is declared error C4430: missing type specifier - int assumed. Note: C++ does not support default-int

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  • Applied style in WPF ignores properties.

    - by Quenton Jones
    Here's the conundrum. In two different places in my application, I use a border with the exact same appearance. In an never-ending fight against code bloat and unmanageable code, I want to define the border's appearance in a style to use when I create the border. Strangely, several of the properties I set are being ignored. Here's the code I use to create the style. Simple enough. Style borderStyle = new Style(typeof(Border)); borderStyle.Setters.Add(new Setter(Border.BorderBrushProperty, Brushes.Black)); borderStyle.Setters.Add(new Setter(Border.BorderThicknessProperty, new Thickness(4))); borderStyle.Setters.Add(new Setter(Border.OpacityProperty, 1.0)); return borderStyle; But when I set the style, the opacity property is left at its original value of 0.7. I have also tried setting the background of the border to a brush I created. It too is ignored. Thanks for any insights you may have.

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  • Storing multiple discarded datas in a single variable using a string accumulator

    - by dan
    For an assignment for my intro to python course, we are to write a program that generates 100 sets of x,y coordinates. X must be a float between -100.0 and 100.0 inclusive, but not 0. Y is Y = ((1/x) * 3070) but if the absolute value of Y is greater than 100, both numbers must be discarded (BUT STORED) and another set generated. The results must be displayed in a table, and then after the table, the discarded results must be shown. The teacher said we should use a "string accumulator" to store the discarded data. This is what I have so far, and I'm stuck at storing the discarded data. # import random.py import random # import math.py import math # define main def main(): x = random.uniform(-100.0, 100.0) while x == 0: x = random.uniform(-100.0, 100.0) y = ((1/x) * 3070) while math.fabs(y) > 100: xDiscarded = yDiscarded = y = ((1/x) * 3070) As you can see, I run into the problem of when abs(y) 100, I'm not too sure how to store the discarded data and let it accumulate every time abs(y) 100. I'm cool with the data being stored as "351.2, 231.1, 152.2" I just don't know how to turn the variable into a string and store it. We haven't learned arrays yet so I can't do that. Any help would be much appreciated. Thanks!

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  • Why does Go not seem to recognize size_t in a C header file?

    - by Graeme Perrow
    I am trying to write a go library that will act as a front-end for a C library. If one of my C structures contains a size_t, I get compilation errors. AFAIK size_t is a built-in C type, so why wouldn't go recognize it? My header file looks like: typedef struct mystruct { char * buffer; size_t buffer_size; size_t * length; } mystruct; and the errors I'm getting are: gcc failed: In file included from <stdin>:5: mydll.h:4: error: expected specifier-qualifier-list before 'size_t' on input: typedef struct { char *p; int n; } _GoString_; _GoString_ GoString(char *p); char *CString(_GoString_); #include "mydll.h" I've even tried adding either of // typedef unsigned long size_t or // #define size_t unsigned long in the .go file before the // #include, and then I get "gcc produced no output". I have seen these questions, and looked over the example with no success.

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  • fgets throwing unhandled exception while parsing stl

    - by user3478400
    I am new to c++, I am trying to parse a stl file which is of about 64MB and has about ~18K lines in it. The code works fine for first few 100 lines but then fgets throws following exception: "Unhandled exception at 0x77B0BAC5 (ntdll.dll) in STLparser.exe: 0xC0000024: There is a mismatch between the type of object required by the requested operation and the type of object that is specified in the request." I have checked manually the line for which fgets throws exception, there is nothing out of ordinary there. I am out of options for now. Any help to fix this issue will be greatly appreciated. ================CODE========================== #include<fstream> #include<iostream> #include"ParseString.h" #include"Vectors.h" using namespace std; int main(void) { //Define variables FILE *file; char *line = new char; parsestring oneline; int n_Vols = 0, n_Elms = 0, n_nods = -1, E = 0; Nod *nodes = new Nod(); Nod dummy; Elm *elements = new Elm(); int mycounter = 0; //Open file fopen_s(&file, "sample.stl", "r"); while (fgets(line, 1024, file) != NULL) //**********Getting Error Here************* { // populate required data } fclose(file); printf("%d,%d,%d", n_Vols, n_Elms, n_nods); getchar(); return 0; } ===================When broken, execution resumes at this function (not my function, something internal) void __cdecl _unlock ( int locknum ) { /* * leave the critical section. */ LeaveCriticalSection( _locktable[locknum].lock ); }

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  • Is there a jQuery Equivalent of YUI 2 Custom Event Publish/Subscribe Event Model?

    - by Abe
    Hello! I learned how to develop in Javascript using the YUI 2 library and was wondering if there is a jQuery equivalent of Custom Events (http://developer.yahoo.com/yui/event/#customevent) Specifically, I want to be able to define custom events without having to attach the listeners initially. In YUI, I would create a page class and declare different custom events that can be subscribed to. Below is some example code to demonstrate what I want to do, but with jQuery function ListPage() { var me = this; this.initEvent = new YAHOO.util.CustomEvent("initEvent"); this.init = function() { // initialize events, DOM, etc this.initEvent.fire(me); } } In application Javascript, I would then like to subscribe to the initEvent. var page = new ListPage(); page.initEvent.subscribe( function (type, args) { // do stuff here } ); page.init(); Are there any tutorials/examples of something this in jQuery? I understand I can do something similar using bind() and trigger(), but the impression I get is I have to pass in the event handler when I call bind(). Is it possible in jQuery to create the custom event, but pass in the event handler later? I hope my question makes sense. thanks!

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  • how to create an object using self?

    - by Nick
    I thought I understood the use of self while referring to anything in the current class. After encountering this warning and subsequent run failure, I have googled many variants of "define self" or "usage of self" and gotten nowhere. This problem is how to create an object without the warning, and understand why. #import <Cocoa/Cocoa.h> @interface Foo : NSObject { Foo *obj; } -(void)beta; @end #import "Foo.h" @implementation Foo -(void)beta{ obj = [self new]; // 'Foo' may not respond to '-new' } @end Note, if I substitute Foo for self, there's no problem. I thought the class name and self were equivalent, but obviously the compiler doesn't think so. Perhaps an explanation of what's wrong here will not only solve my problem but also enlighten my understanding of the usage of self. Are there any tutorials about proper usage of self? I couldn't find anything beyond something like "self is the receiver of the message," which I didn't help me at all.

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  • Project Euler #119 Make Faster

    - by gangqinlaohu
    Trying to solve Project Euler problem 119: The number 512 is interesting because it is equal to the sum of its digits raised to some power: 5 + 1 + 2 = 8, and 8^3 = 512. Another example of a number with this property is 614656 = 28^4. We shall define an to be the nth term of this sequence and insist that a number must contain at least two digits to have a sum. You are given that a2 = 512 and a10 = 614656. Find a30. Question: Is there a more efficient way to find the answer than just checking every number until a30 is found? My Code int currentNum = 0; long value = 0; for (long a = 11; currentNum != 30; a++){ //maybe a++ is inefficient int test = Util.sumDigits(a); if (isPower(a, test)) { currentNum++; value = a; System.out.println(value + ":" + currentNum); } } System.out.println(value); isPower checks if a is a power of test. Util.sumDigits: public static int sumDigits(long n){ int sum = 0; String s = "" + n; while (!s.equals("")){ sum += Integer.parseInt("" + s.charAt(0)); s = s.substring(1); } return sum; } program has been running for about 30 minutes (might be overflow on the long). Output (so far): 81:1 512:2 2401:3 4913:4 5832:5 17576:6 19683:7 234256:8 390625:9 614656:10 1679616:11 17210368:12 34012224:13 52521875:14 60466176:15 205962976:16 612220032:17

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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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  • 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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