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• c++ - what is faster ?

  - by VaioIsBorn

  If we have the following 2 snippets of code in c++ that do the same task: int a, b=somenumber; while(b > 0) { a = b % 3; b /= 3; } or int b=somenumber; while(b > 0) { int a=b%3; b /= 3; } I don't know much about computer architecture/c++ design, but i think that the first code is faster because it declares the integer a at the beginning and just uses it in the while-loop, and in the second code the integer a is being declared everytime the while-loop starts over. Can some one help me with this, am i correct or what and why ?

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• Is a Critical Section around an integer getter and setter redundant?

  - by Tim Gradwell

  Do critical sections inside trivial int accessors actually do anything useful? int GetFoo() { CriticalSection(crit_id); return foo; } void SetFoo(int value) { CriticalSection(crit_id); foo = value; } Is it possible for two threads to be attempting to read and write foo simultaneously? I'd have thought 'no' unless integers are written byte-at-a-time, in which case I can see the use. But I'd have though modern cpus would read/write integers in a single atomic action...

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• What is the problem with this code?

  - by eSKay

  #include<stdio.h> class A { public: int a;}; class B: public A { public: static int b; B(){ b++; printf("B:%d\n",b); } }; int main() { A* a1 = new B[100]; A* a2 = new B(); return 0; } Error: In function `main': undefined reference to `B::b' undefined reference to `B::b' undefined reference to `B::b' undefined reference to `B::b'

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• Can't compile std::map sorting, why?

  - by Vincenzo

  This is my code: map<string, int> errs; struct Compare { bool operator() (map<string, int>::const_iterator l, map<string, int>::const_iterator r) { return ((*l).second < (*r).second); } } comp; sort(errs.begin(), errs.end(), comp); Can't compile. This is what I'm getting: no matching function for call to ‘sort(..’ Why so? Can anyone help? Thanks!

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• Extract inputs from a pointer to array of characters in C / C++

  - by user2066884

  I am writing a command line utility but I cannot find a way to store the commands and arguments. so far I have the following but I get a Segmentation fault: int main(void) { char *command; char *args[MAX_LINE/2 + 1]; int should_run = 1; do{ cout << "cmd> "; int counter = 0; while(cin >> command) { strcpy(args[counter],command); counter++; } cout << args[0] << "\n"; } }

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• array of objects of a class

  - by anurag18294

  #include class test{ int a; char b; public: test() { cout<<"\n\nDefault constructor being called"; } test(int i,char j) { a=i; b=j; cout<<"\n\nConstructor with arguments called"; } }; int main() { test tarray[5]; test newobj(31,'z'); }; In the above code snippet can we intialize values to tarray[5].

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• In a C++ template, is it allowed to return an object with specific type parameters?

  - by nieldw

  When I've got a template with certain type parameters, is it allowed for a function to return an object of this same template, but with different types? In other words, is the following allowed? template<class edgeDecor, class vertexDecor, bool dir> Graph<edgeDecor,int,dir> Graph<edgeDecor,vertexDecor,dir>::Dijkstra(vertex s, bool print = false) const { /* Construct new Graph with apropriate decorators */ Graph<edgeDecor,int,dir> span = new Graph<edgeDecor,int,dir>(); /* ... */ return span; }; If this is not allowed, how can I accomplish the same kind of thing?

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• SQL Server 15MM rows, simple COUNT query. 15+ seconds?

  - by john

  We took over a website from another company after a client decided to switch. We have a table that grows by about 25k records a day, and is currently at 15MM records. The table looks something like: id (PK, int, not null) member_id (int, not null) another_id (int, not null) date (datetime, not null) SELECT COUNT(id) FROM tbl can take up to 15 seconds. A simple inner join on 'another_id' takes over 30 seconds. I can't imagine why this is taking so long. Any advice? SQL Server 2005 Express

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• What is the purpose of AnyVal?

  - by DaoWen

  I can't think of any situation where the type AnyVal would be useful, especially with the addition of the Numeric type for abstracting over Int, Long, etc. Are there any actual use cases for AnyVal, or is it just an artifact that makes the type hierarchy a bit prettier? Just to clarify, I know what AnyVal is, I just can't think of any time that I would actually need it in Scala. When would I ever need a type that encompassed Int, Character and Double? It seems like it's just there to make the type hierarchy prettier (i.e. it looks nicer to have AnyVal and AnyRef as siblings rather than having Int, Character, etc. inherit directly from Any).

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• Missing MethodInfo for overloaded function with different return type

  - by Charvak

  I have a class defined as follows interface ITest { List<T> Find<T>(int i); } class Test: ITest { public T List<T> Find<T>(int i) { return default(T); } List<T> ITest.Find<T>(int i) { return null; } } When I use typeof(Test).GetMethods() (both with and without appropriate BindingFlags) I do not get the MethodInfo for ITest.Find function. What is the best way of getting the MethodInfo for the missing method? Thanks

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• to store char* from function return value

  - by samprat

  Hi folks, I am trying to implement a function which reads from Serial Port ( Linux) and retuns char*. The function works fine but how would I store return value from function. example of function is char *ReadToSerialPort() { char *bufptr; char buffer[256]; // Input buffer/ / //char *bufptr; // Current char in buffer // int nbytes; // Number of bytes read // bufptr = buffer; while ((nbytes = read(fd, bufptr, buffer+sizeof(buffer)-bufptr -1 )) > 0) { bufptr += nbytes; // if (bufptr[-1] == '\n' || bufptr[-1] == '\r') /*if ( bufptr[sizeof(buffer) -1] == '*' && bufptr[0] == '$' ) { break; }*/ } // while ends if ( nbytes ) return bufptr; else return 0; *bufptr = '\0'; } // end ReadAdrPort //In main int main( int argc , char *argv[]) { char *letter; if(strcpy(letter, ReadToSerialPort()) >0 ) { printf("Response is %s\n",letter); } }

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• question regarding "this" pointer in c++

  - by sil3nt

  hello there, i have been given class with int variables x and y in private, and an operator overload function, class Bag{ private: int x; int y; public: Bag(); ~Bag(); //....... //.....etc }; Bag operator+ (Bag new) const{ Bag result(*this); //what does this mean? result.x += new.x; result.y += new.y; } What is the effect of having "Bag result(*this);" there?.

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• problem with Expression not equal types

  - by user428547

  class first { private int? firstID; } class second { private int secondID; private int secondField; } public override Expression<Func<first, bool>> FirstFilter() { Contex db = new Contex(); List<second> list = (from p in db.second select p).ToList(); return b => list.Select(p => p.secondID).Contains(b.firstID); } and i have error: cannot convert from 'System.Collections.Generic.IEnumerable' to 'System.Collections.Generic.IEnumerable' i have tried many diferent ways, but i just don't know how can i fix it.

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• Android-SQLite: How to Count specific value from Column?

  - by sanpatil

  I have two table (TABLE_EXAM,TABLE_RESULT). Here is value of my TABLE_RESULT. result_id exam_id question_id correct_answer 1 2 4 y 2 2 5 y 3 2 6 n 4 2 7 y I need to count how many correct_answer='y' where exam_id=2. I try following code but it return 0. public int calculateResult(int examId,String confirmAnswer) { int correctAnswer=0; try { SQLiteDatabase db=this.getWritableDatabase(); String selectQuery=("select count(correctAnswer) from result where exam_id ='" + examId + "' and correctAnswer ='" + 'y' +"'" ); // String selectQuery=("SELECT COUNT(*)FROM result WHERE exam_id ='" + examId + "' and correctAnswer ='" + confirmAnswer +"'" ); Cursor cursor = db.rawQuery(selectQuery, null); if(cursor.moveToLast()) { correctAnswer=cursor.getInt(3); } } catch(Exception e) { e.printStackTrace(); } return correctAnswer; } In variable confirm_answer i pass "y". Give me some hint or reference. Any help is appreciated. Thanks in Advance

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• IEnumerable<SelectListItem> error question

  - by user281180

  I have the following code, but i`m having error of Error 6 foreach statement cannot operate on variables of type 'int' because 'int' does not contain a public definition for 'GetEnumerator' C:\Dev\DEV\Code\MvcUI\Models\MappingModel.cs 100 13 MvcUI How can I solve this? Note: string [] projectID; Class Employee { int id {get; set;} string Name {get;set;} } public IEnumerable<SelectListItem> GetStudents() { List<SelectListItem> result = new List<SelectListItem>(); foreach (var id in Convert.ToInt32(projectID)) { foreach( Employee emp in Project.Load(id)) result.Add(new SelectListItem { Selected = false, Text = emp.ID.ToString(), Value = emp.Name }); return result.AsEnumerable(); } }

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• c++: at what point should I start using "new char[N]" vs a static buffer "char[Nmax]"

  - by dan

  My question is with regard to C++ Suppose I write a function to return a list of items to the caller. Each item has 2 logical fields: 1) an int ID, and 2) some data whose size may vary, let's say from 4 bytes up to 16Kbytes. So my question is whether to use a data structure like: struct item { int field1; char field2[MAX_LEN]; OR, rather, to allocate field2 from the heap, and require the caller to destroy when he's done: struct item{ int field1; char *field2; // new char[N] -- destroy[] when done! Since the max size of field #2 is large, is makes sense that this would be allocated from the heap, right? So once I know the size N, I call field2 = new char[N], and populate it. Now, is this horribly inefficient? Is it worse in cases where N is always small, i.e. suppose I have 10000 items that have N=4?

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• error defining foreign key PhpMyAdmin

  - by Ngounou lassale

  I am new to PhpMyAdmin. I will like to create a foreign key for my tables. In fact i have create tableI with this structures(A as int(11) autoincrement, B as varchar) TableII ( A_2 as int(11) auto increment, B_2 as varchar, A as int(11). I have declared A as an index in tableII, now when i go to relationship view to precise A as a foreign key i always have this error Erreur lors de la création de la clé étrangère sur ID_Ville (vérifiez le type des colonnes) Erreur ALTER TABLE tb_quartier ADD FOREIGN KEY ( ID_Ville ) REFERENCES ingenieris2.tb_ville ( ID_Ville ) ON DELETE RESTRICT ; Please Help thanks!

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• conversions in C++

  - by lego69

  I have this snippet of the code: header class A { private: int player; public: A(int initPlayer = 0); A(const A&); A& operator=(const A&); ~A(); void foo() const; friend A& operator=(A& i, const A& member); }; operator= A& operator=(A& i, const A& member){ i(member.player); return i; } and I have row in my code: i = *pa1; A *pa1 = new A(a2); at the beginning i was int how can I fix it, thanks in advance I have an error must be non-static function

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• C++ file including C header file

  - by fdeslaur

  I need to include a C header file in my C++ project but g++ throws "not declared in this scope" errors. I read that i need to use extern "C" keyword to fix it but it didn't seem to work for me. Here is a dummy example triggering this error. main.cpp: #include <iostream> extern "C" { #include "includedFile.h" } int main() { int a = 2; int b = 1212; std::cout<< "Hello World!\n"; return 0; } includedFile.h #include <stdint.h> enum TypeOfEnum { ONE, TWO, THREE, FOUR = INT32_MAX, }; The error thrown is : $> g++ main.cpp In file included from main.cpp:4:0: includedFile.h:7:9: error: ‘INT32_MAX’ was not declared in this scope FOUR = INT32_MAX, I saw on this post that I may need #define __STDC_LIMIT_MACROS without any success. Any help is welcome!

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• Cutting Row with Data and moving to different sheet VBA

  - by user3709645

  I'm trying to cut a row that has the specified cell blank and then paste it into another sheet in the same workbook. My coding works fine to delete the row but everything I've tried to cut and paste keeps giving me errors. Here's the working code that deletes the rows: Sub Remove() 'Remove No Denovo &/or No Peak Seq Dim n As Long Dim nLastRow As Long Dim nFirstRow As Long Dim lastRow As Integer ActiveSheet.UsedRange Set r = ActiveSheet.UsedRange nLastRow = r.rows.Count + r.Row - 1 nFirstRow = r.Row For n = nLastRow To nFirstRow Step -1 If Cells(n, "G") = "" Then Cells(n, "G").EntireRow.Delete Next n End Sub Thanks for any help!

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• Obtaining frame pointer in C

  - by assketchum

  I'm trying to get the FP in my C program, I tried two different ways, but they both differ from what I get when I run GDB. The first way I tried, I made a protocol function in C for the Assembly function: int* getEbp(); and my code looks like this: int* ebp = getEbp(); printf("ebp: %08x\n", ebp); // value i get here is 0xbfe2db58 while( esp <= ebp ) esp -= 4; printf( "ebp: %08x, esp" ); //value i get here is 0xbfe2daec My assembly code getEbp: movl %ebp, %eax ret I tried making the prototype function to just return an int, but that also doesn't match up with my GDB output. We are using x86 assembly. EDIT: typos, and my getEsp function looks exactly like the other one: getEsp: movl %esp, %eax ret

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• Weird output as the numbers get bigger in Fibonacci sequence

  - by Jon

  I noticed in my fibonacci sequence that I'm getting negative numbers after a certain point. Does this have to do with the limited range of "int"? or is there something wrong with my code? Here is the code: using std::cout; int main() { int n = 50, f1 = 0, f2 = 1, fn = 0, i = 0; cout << "0 "; for (i = 0; i < n; i++) { fn = f1 + f2; f2 = f1; f1 = fn; cout << fn << " "; }

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• C++: How to design a utility class?

  - by Martijn Courteaux

  Hi, The title says it all. But I don't know if I should go for static methods, just a header, a class, or something else? What would be best practice? But, I don't want to have an instance of a utility class. I want to add functions like: Uint32 MapRGB (int r, int g, int b); const char* CopyString(const char* char); // etc. You know: utility methods...

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• C Struct as an argument

  - by Brian

  I'm wondering what's the difference between sample1 and sample2. Why sometimes I have to pass the struct as an argument and sometimes I can do it without passing it in the function? and how would it be if samplex function needs several structs to work with? would you pass several structs as an argument? struct x { int a; int b; char *c; }; void sample1(struct x **z;){ printf(" first member is %d \n", z[0]->a); } void sample2(){ struct x **z; printf(" first member is %d \n", z[0]->a); // seg fault } int main(void) { struct x **z; sample1(z); sample2(); return 0; }

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• casting a node to integer

  - by user1708762

  The code gives an error saying that "no operator matches these two operands" in the if comparison statement. I interpret,it should mean that "a node can't be converted/casted into an integer". But, the print statement prints an integer value for w[2] when used with %d format. Why is that happening? Isn't printf casting it? NODE *w=(NODE *)malloc(4*sizeof(NODE)); if(w[2]==0) printf("%d\n",w[2]); The structure of the node is- struct node{ int key; struct node *father; struct node *child[S]; int *ss; int current; };

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