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  • Can i have a negative value as constant expression in Scala?

    - by Klinke
    I have an Java-Annotation that return a double value: @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.FIELD) public @interface DoubleValue { double value(); } When i try to attach the annotation to a field in a scala class and the value is negativ like here: class Test { @DoubleValue(-0.05) var a = _ } i get an compiler error with the message: "annotation argument needs to be a constant; found: 0.05.unary_-". I understood that i need a numerical literal and i looked into the Scala Language Specification and it seems, that the - sign is only used for the exponent but not for the mantissa. Does someone has an idea how i can have a negative value as runtime information using annotations? Thanks, Klinke

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  • Is the old vector get cleared? If yes, how and when?

    - by user180866
    I have the following code: void foo() { vector<double> v(100,1); // line 1 // some code v = vector<double>(200,2); // line 2 // some code } what happened to the vector of size 100 after the second line? Is it gets cleared by itself? If the answer is yes, how and when it is cleared? By the way, is there any other "easy and clean" ways to change the vector as in line 2? I don't want things like v.resize(200); for (int i=0; i<200; i++) v[i] = 2;

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  • How to use the vtable to determine class type

    - by Alex Silverman
    I was recently on an interview for a position where C/C++ is the primary language and during one question I was told that it's possible to use the vtable to determine which class in a hierarchy a base pointer actually stores. So if, for example you have class A { public: A() {} virtual ~A() {} virtual void method1() {} }; class B : public A { public: B() {} virtual ~B() {} virtual void method1() {} }; and you instantiate A * pFoo = new B(), is it indeed possible to use the vtable to determine whether pFoo contains a pointer to an instance of A or B?

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  • What's the C strategy to "imitate" a C++ template ?

    - by Andrei Ciobanu
    After reading some examples on stackoverflow, and following some of the answers for my previous questions (1), I've eventually come with a "strategy" for this. I've come to this: 1) Have a declare section in the .h file. Here I will define the data-structure, and the accesing interface. Eg.: /** * LIST DECLARATION. (DOUBLE LINKED LIST) */ #define NM_TEMPLATE_DECLARE_LIST(type) \ typedef struct nm_list_elem_##type##_s { \ type data; \ struct nm_list_elem_##type##_s *next; \ struct nm_list_elem_##type##_s *prev; \ } nm_list_elem_##type ; \ typedef struct nm_list_##type##_s { \ unsigned int size; \ nm_list_elem_##type *head; \ nm_list_elem_##type *tail; \ int (*cmp)(const type e1, const type e2); \ } nm_list_##type ; \ \ nm_list_##type *nm_list_new_##type##_(int (*cmp)(const type e1, \ const type e2)); \ \ (...other functions ...) 2) Wrap the functions in the interface inside MACROS: /** * LIST INTERFACE */ #define nm_list(type) \ nm_list_##type #define nm_list_elem(type) \ nm_list_elem_##type #define nm_list_new(type,cmp) \ nm_list_new_##type##_(cmp) #define nm_list_delete(type, list, dst) \ nm_list_delete_##type##_(list, dst) #define nm_list_ins_next(type,list, elem, data) \ nm_list_ins_next_##type##_(list, elem, data) (...others...) 3) Implement the functions: /** * LIST FUNCTION DEFINITIONS */ #define NM_TEMPLATE_DEFINE_LIST(type) \ nm_list_##type *nm_list_new_##type##_(int (*cmp)(const type e1, \ const type e2)) \ {\ nm_list_##type *list = NULL; \ list = nm_alloc(sizeof(*list)); \ list->size = 0; \ list->head = NULL; \ list->tail = NULL; \ list->cmp = cmp; \ }\ void nm_list_delete_##type##_(nm_list_##type *list, \ void (*destructor)(nm_list_elem_##type elem)) \ { \ type data; \ while(nm_list_size(list)){ \ data = nm_list_rem_##type(list, tail); \ if(destructor){ \ destructor(data); \ } \ } \ nm_free(list); \ } \ (...others...) In order to use those constructs, I have to create two files (let's call them templates.c and templates.h) . In templates.h I will have to NM_TEMPLATE_DECLARE_LIST(int), NM_TEMPLATE_DECLARE_LIST(double) , while in templates.c I will need to NM_TEMPLATE_DEFINE_LIST(int) , NM_TEMPLATE_DEFINE_LIST(double) , in order to have the code behind a list of ints, doubles and so on, generated. By following this strategy I will have to keep all my "template" declarations in two files, and in the same time, I will need to include templates.h whenever I need the data structures. It's a very "centralized" solution. Do you know other strategy in order to "imitate" (at some point) templates in C++ ? Do you know a way to improve this strategy, in order to keep things in more decentralized manner, so that I won't need the two files: templates.c and templates.h ?

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  • Is there a way to use template specialization to separate new from new[]?

    - by Marlon
    I have an auto pointer class and in the constructor I am passing in a pointer. I want to be able to separate new from new[] in the constructor so that I can properly call delete or delete[] in the destructor. Can this be done through template specialization? I don't want to have to pass in a boolean in the constructor. template <typename T> class MyAutoPtr { public: MyAutoPtr(T* aPtr); }; // in use: MyAutoPtr<int> ptr(new int); MyAutoPtr<int> ptr2(new int[10]);

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  • Inheritance - initialization problem

    - by dumbquestion
    I have a c++ class derived from a base class in a framework. The derived class doesn't have any data members because I need it to be freely convertible into a base class and back - the framework is responsible for loading and saving the objects and I can't change it. My derived class just has functions for accessing the data. But there are a couple of places where I need to store some temporary local variables to speed up access to data in the base class. mydata* MyClass::getData() { if ( !m_mydata ) { // set to NULL in the constructor m_mydata = some_long_and complex_operation_to_get_the_data_in_the_base() } return m_mydata; } The problem is if I just access the object by casting the base class pointer returned from the framework to MyClass* the ctor for MyClass is never called and m_mydata is junk. Is there a way of only initializing the m_mydata pointer once?

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  • MinMax Heap implementation without an array

    - by user576531
    Hi. I found lots of MinMax Heap implementations, that were storing data in an array. It is realy easy to implement, that is way I am looking for something different. I want to create a MinMax Heap using only elements of the Heap with pointers to left child and right child (and afcourse a key to compare). So the Heap have only pointer to the root object (min level), and a root object have a pointer to his children (max level) and so on. I know how to insert a new object (finding a proper path by using binary represenation of int depending on Heap size), but I don't know how to implement the rest (push up (down) the element, find parent or grandparent). Thx for help

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  • Why wont my while loop wont take new input (c++)

    - by Van
    I've written a program to get a string input from a user and parse it into tokens and move a robot according to the input. My problem is trying to issue more than one command. The code looks like: void Navigator::manualDrive() { const int bufSize = 42; char uinput[bufSize]; char delim[] = " "; char *token; while(true) { Navigator::parseInstruction(uinput); } } /* parseInstruction(char *c) -- parses cstring instructions received * and moves robot accordingly */ void Navigator::parseInstruction(char * c) { const int bufSize = 42; char uinput[bufSize]; char delim[] = " "; char *token; cout << "Enter your directions below: \n"; cin.ignore(); cin.getline (uinput, bufSize); token=strtok(uinput, delim); if(strcmp("forward", token) == 0) { int inches; token = strtok(NULL, delim); inches = atoi (token); Navigator::travel(inches); } if(strcmp("back",token) == 0) { int inches; token = strtok(NULL, delim); inches = atoi (token); double value = fabs(0.0735 * fabs(inches) - 0.0550); myRobot.backward(1/*speed*/, value/*time*/); } if(strcmp("turn",token) == 0) { int degrees; token = strtok(NULL, delim); if(strcmp("left",token) == 0) { token = strtok(uinput, delim); degrees = atoi (token); double value = fabs(0.0041 * degrees - 0.0523); myRobot.turnLeft(1/*speed*/, value/*time*/); } } if(strcmp("turn",token) == 0) { int degrees; token = strtok(NULL, delim); if(strcmp("right",token) == 0) { token = strtok(uinput, delim); degrees = atoi (token); double value = fabs(0.0041 * degrees - 0.0523); myRobot.turnRight(1/*speed*/, value/*time*/); } } if(strcmp("stop",token) == 0) { myRobot.motors(0,0); } } In the function manualDrive I have a while loop calling the function parseInstruction infinitely. The program outputs "Enter your directions below: " When I give the program instructions it executes them, and then it outputs "enter your directions below: " again and when I input my directions again it does not execute them and outputs "Enter your directions below: " instead. I'm sure this is a very simple fix I'm just very new to c++. So if you could please help me out and tell me why the program only takes the first set of directions. thanks

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  • C++ inheritance and member function pointers

    - by smh
    In C++, can member function pointers be used to point to derived (or even base) class members? EDIT: Perhaps an example will help. Suppose we have a hierarchy of three classes X, Y, Z in order of inheritance. Y therefore has a base class X and a derived class Z. Now we can define a member function pointer p for class Y. This is written as: void (Y::*p)(); (For simplicity, I'll assume we're only interested in functions with the signature void f() ) This pointer p can now be used to point to member functions of class Y. This question (two questions, really) is then: Can p be used to point to a function in the derived class Z? Can p be used to point to a function in the base class X?

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  • C++ : size of int, long, etc...

    - by Jérôme
    I'm looking for detailed informations regarding the size of basic C++ types. I know that it depends on the architecture (16 bits, 32 bits, 64 bits) and the compiler. But are there any standards ? I'm using Visual Studio 2008 on a 32 bit achitecture. Here is what I get : char : 1 byte short : 2 bytes int : 4 bytes long : 4 bytes float : 4 bytes double : 8 bytes I tried to find, without much success, reliable informations telling the sizes of char, short, int , long, double, float (and other types I don't think of) under different architecture and compiler.

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  • Remove from a std::set<shared_ptr<T>> by T*

    - by Autopulated
    I have a set of shared pointers: std::set<boost::shared_ptr<T>> set; And a pointer: T* p; I would like to efficiently remove the element of set equal to p, but I can't do this with any of the members of set, or any of the standard algorithms, since T* is a completely different type to boost::shared_ptr<T>. A few approaches I can think of are: somehow constructing a new shared_ptr from the pointer that won't take ownership of the pointed to memory (ideal solution, but I can't see how to do this) wrapping / re-implementing shared_ptr so that I can do the above just doing my own binary search over the set Help!

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  • Code crashing compiler: main() returning a struct instead of an int

    - by AndrejaKo
    Hi! I'm experimenting with a piece of C code. Can anyone tell me why is VC 9.0 with SP1 crashing for me? Oh, and the code is meant to be an example used in a discussion why something like void main (void) is evil. struct foo { int i; double d; } main (double argc, struct foo argv) { struct foo a; a.d=0; a.i=0; return a.i; } If I put return a; compiler doesn't crash.

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  • For-Each and Pointers in Java

    - by John
    Ok, so I'm tyring to iterate through an ArrayList and remove a specefic element. However, I am having some trouble using the For-Each like structure. When I run the following code: ArrayList<String> arr = new ArrayList<String>(); //... fill with some values (doesn't really matter) for(String t : arr) { t = " some other value "; //hoping this would change the actual array } for(String t : arr) { System.out.println(t); //however, I still get the same array here } My question in, how can I make 't' a pointer to 'arr' so that I am able to change the values in a for-each loop? I know I could loop through the ArrayList using a different structure, but this one looks so clean and readable, it would just be nice to be able to make 't' a pointer. All comments are appreciated! Even if you say I should just suck it up and use a different construct.

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  • Multiple word Auttosuggest using Lucene.Net

    - by eric
    I am currently working on an search application which uses Lucene.Net to index the data from the database to Index file. I have a product catalog which has Name, short and long description, sku and other fields. The data is stored in Index using StandardAnalyzer. I am trying to add auto suggestion for a text field and using TermEnum to get all the keyword terms and its score from the Index. But the terms returned are of single term. For example, if I type for co, the suggestion returned are costume, count, collection, cowboy, combination etc. But I want the suggestion to return phrases. For exmaple, if I search for co, the suggestions should be cowboy costume, costume for adults, combination locks etc. The following is the code used to get the suggestions: public string[] GetKeywords(string strSearchExp) { IndexReader rd = IndexReader.Open(mIndexLoc); TermEnum tenum = rd.Terms(new Term("Name", strSearchExp)); string[] strResult = new string[10]; int i = 0; Dictionary<string, double> KeywordList = new Dictionary<string, double>(); do { //terms = tenum.Term(); if (tenum.Term() != null) { //strResult[i] = terms.text.ToString(); KeywordList.Add(tenum.Term().text.ToString(), tenum.DocFreq()); } } while (tenum.Next() && tenum.Term().text.StartsWith(strSearchExp) && tenum.Term().text.Length > 1); var sortedDict = (from entry in KeywordList orderby entry.Value descending select entry); foreach (KeyValuePair<string, double> data in sortedDict) { if (data.Key.Length > 1) { strResult[i] = data.Key; i++; } if (i >= 10) //Exit the for Loop if the count exceeds 10 break; } tenum.Close(); rd.Close(); return strResult; } Can anyone please give me directions to achive this? Thanks for looking into this.

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  • Program crash for array copy with ifort

    - by Stefano Borini
    This program crashes with Illegal instruction: 4 on MacOSX Lion and ifort (IFORT) 12.1.0 20111011 program foo real, pointer :: a(:,:), b(:,:) allocate(a(5400, 5400)) allocate(b(5400, 3600)) a=1.0 b(:, 1:3600) = a(:, 1:3600) print *, a print *, b deallocate(a) deallocate(b) end program The same program works with gfortran. I don't see any problem. Any ideas ? Unrolling the copy and performing the explicit loop over the columns works in both compilers. Note that with allocatable instead of pointer I have no problems. The behavior is the same if the statement is either inside a module or not. I confirm the same behavior on Linux using ifort (IFORT) 12.1.3 20120130.

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  • Some issue with bufferedReader

    - by thetna
    I have a java function as follows: public HashMap<String, ArrayList<Double>> embedWords(BufferedReader buffR1 { ArrayList<String > arrayList = new ArrayList<String>(); arrayList = getWords(buffR1); System.out.println("Word size:"+ arrayList.size()); ArrayList<ArrayList<Double>> arrList = getWordFeature(buffR1); System.out.println("Size of arrList:embedWords:"+arrList.size()); } Here , the problem is , the both of the function getWords and getWordFeatures can't give the size value. When i comment function getWords the function getWordFeature returns non-zero value .But when uncommented , the output is as follows: Word size:15055 Size of arrList:embedWords: 0

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  • Operator() as a subscript (C++)

    - by Ivan Gromov
    I use operator() as a subscript operator this way: double CVector::operator() (int i) const { if (i >= 0 && i < this->size) return this->data[i]; else return 0; } double& CVector::operator() (int i) { return (this->data[i]); } It works when I get values, but I get an error when I try to write assign a value using a(i) = 1; UPD: Error text: Unhandled exception at 0x651cf54a (msvcr100d.dll) in CG.exe: 0xC0000005: Access violation reading location 0xccccccc0.

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  • "SQLSTATE[23000]: Integrity constraint violation" in Doctrine

    - by rags
    Hi, i do get an Integrity constraint violation for Doctrine though i really can't see why. Schema.yml User: columns: id: type: integer primary: true autoincrement: true username: type: varchar(64) notnull: true email: type: varchar(128) notnull: true password: type: varchar(128) notnull: true relations: Websites: class: Website local: id foreign: owner type: many foreignType: one onDelete: CASCADE Website: columns: id: type: integer primary: true autoincrement: true active: type: bool owner: type: integer notnull: true plz: type: integer notnull: true longitude: type: double(10,6) notnull: true latitude: type: double(10,6) notnull: true relations: Owner: type: one foreignType: many class: User local: owner foreign: id And here's my data Fixtures (data.yml) Model_User: User_1: username: as email: as****.com password: ***** Model_Website: Website_1: active: true plz: 34222 latitude: 13.12 longitude: 3.56 Owner: User_1

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  • Split text files Accross threads

    - by Kevin
    The problem: I have a few text files (10) with numbers in them on every line. I need to have them split across some threads I create using the pthread library. these threads that are created (worker threads) are to find the largest prime number that gets sent to them (and over all the largest prime from all of the text files). My current thoughts on solutions: I am thinking myself to have two arrays and all of the text files in one array and the other array will contain a binary file that I can read say 1000 lines and send the pointer to the index of that binary file in a struct that contains the id, file pointer, and file position and let it crank through that. a little bit of what I am talking about pthread_create(&threads[index],NULL,calc_sqrt,(void *)threadFields[index]);//Pass struct to each worker Struct: typedef struct threadFields{ int *id, *position; FILE *Fin; }tField; If anyone has any insight or a better solution it would be greatly appreciated Thanks

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  • Somewhat newb question about assy and the heap.

    - by Eric M
    Ultimately I am just trying to figure out how to dynamically allocate heap memory from within assembly. If I call Linux sbrk() from assembly code, can I use the address returned as I would use an address of a statically (ie in the .data section of my program listing) declared chunk of memory? I know Linux uses the hardware MMU if present, so I am not sure if what sbrk returns is a 'raw' pointer to real RAM, or is it a cooked pointer to RAM that may be modified by Linux's VM system? I read this: How are sbrk/brk implemented in Linux?. I suspect I can not use the return value from sbrk() without worry: the MMU fault on access-non-allocated-address must cause the VM to alter the real location in RAM being addressed. Thus assy, not linked against libc or what-have-you, would not know the address has changed. Does this make sense, or am I out to lunch?

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  • parsing primitive types using java.util.Scanner

    - by Rich Fluckiger
    I'm new to java so forgive the noob question. I have created a swing application that basically has three input strings in JTextFields: loanAmount, interestRate and loanYears and a single submit button with the EventAction. I'm trying to use the java.util.Scanner to parse the input to primitive types that I can use in calculations. I'm getting an error in NetBeans indicating that my variables are not recognized? should I not be calling System.in? private void submitButtonActionPerformed(java.awt.event.ActionEvent evt) { Scanner keyInput = new Scanner(System.in); while (true) try{ double amount = keyInput.nextDouble(loanAmount.getText()); double interest = keyInput.nextDouble(interestRate.getText()); int years = keyInput.nextInt(loanYears.getText()); } catch (NumberFormatException nfe){ } }

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  • How does Windows' 'Open with' work?

    - by Frederick
    I was under the impression that when you double click a file (or choose 'Open With' from the right click menu), Windows simply calls the application with the filename as the parameter. Something like this: C: App.exe file.abc However, I just double clicked an .xls file and then checked the PEB of the Excel instance that sprang up. To my surprise the commandline did not contain the filename as a parameter. So that set me wondering. What exactly is mechanism Windows uses to have a file opened by a relevant application? Is there a special API that each application that supports such facility must expose?

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  • strange results with /fp:fast

    - by martinus
    We have some code that looks like this: inline int calc_something(double x) { if (x > 0.0) { // do something return 1; } else { // do something else return 0; } } Unfortunately, when using the flag /fp:fast, we get calc_something(0)==1 so we are clearly taking the wrong code path. This only happens when we use the method at multiple points in our code with different parameters, so I think there is some fishy optimization going on here from the compiler (Microsoft Visual Studio 2008, SP1). Also, the above problem goes away when we change the interface to inline int calc_something(const double& x) { But I have no idea why this fixes the strange behaviour. Can anyone explane this behaviour? If I cannot understand what's going on we will have to remove the /fp:fastswitch, but this would make our application quite a bit slower.

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  • error unidentfied identfier "exams" and i dont know why in c++

    - by user320950
    // basic file operations #include <iostream> #include <fstream> using namespace std; void read_file_in_array(int exam[100][3]); double calculate_total(int exam1[], int exam2[], int exam3[]); // function that calcualates grades to see how many 90,80,70,60 //void display_totals(); int main() { int go,go2,go3; go=read_file_in_array(exam); go2=calculate_total(exam1,exam2,exam3); //go3=display_totals(); cout << go,go2,go3; return 0; }/* int display_totals() { int grade_total; grade_total=calculate_total(exam1,exam2,exam3); return 0; } */ double calculate_total(int exam1[],int exam2[],int exam3[]) { int calc_tot,above90=0, above80=0, above70=0, above60=0,i,j; calc_tot=read_file_in_array(exam); for(i=0;i<100;i++) { exam1[i]=exam[100][0]; exam2[i]=exam[100][1]; exam3[i]=exam[100][2]; if(exam1[i] <=90 && exam1[i] >=100) { above90++; cout << above90; } } return exam3[i]; } void read_file_in_array(double exam[100][3]) { ifstream infile; int num, i=0,j=0; infile.open("grades.txt");// file containing numbers in 3 columns if(infile.fail()) // checks to see if file opended { cout << "error" << endl; } while(!infile.eof()) // reads file to end of line { for(i=0;i<100;i++) // array numbers less than 100 { for(j=0;j<3;j++) // while reading get 1st array or element infile >> exam[i][j]; infile >> exam[i][j]; infile >> exam[i][j]; cout << exam[i][j] << endl; } exam[i][j]=exam1[i]; exam[i][j]=exam2[i]; exam[i][j]=exam3[i]; } infile.close(); }

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  • C: using clock() to measure time in multi-threaded programs

    - by Shinka
    I've always used clock() to measure how much time my application took from start to finish, as; int main(int argc, char *argv[]) { const clock_t START = clock(); // ... const double T_ELAPSED = (double)(clock() - START) / CLOCKS_PER_SEC; } Since I've started using POSIX threads this seem to fail. It looks like clock() increases N times faster with N threads. As I don't know how many threads are going to be running simultaneously, this approach fails. So how can I measure how much time has passed ?

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