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• MYSQL Inserting rows that reference main rows.

  - by Andrew M

  I'm transferring my access logs into a database. I've got two tables: urlRequests id : int(10) host : varchar(100) path: varchar(300) unique index (host, path) urlAccesses id : int(10) request : int(10) <-- reference to urlRequests row ip : int(4) query : varchar(300) time : timestamp I need to insert a row into urlAccesses for every page load, but first a row in urlRequests has to exist with the requested host and path so that urlAccesses's row can reference it. I know I can do it this way: A. check if a row exists in urlRequests B. insert a row in urlRequests if it needs it C. insert a row into urlAccesses with the urlRequests's row id referenced That's three queries for every page load if the urlRequests row doesn't exist. I'm very new to MySQL, so I'm guessing that there's a way to go about this that would be faster and use less queries.

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• Showing an image after loading it from sql database

  - by user330075

  I have a problem showing the image form database in a view Details and a ImageController. Inside the view I have: img src=Url.Action("GetFile","Image", new {id= Model.id}) and in controller: public FileContentResult GetFile(int idl) { //int idl = 32; SqlDataReader rdr; byte[] fileContent = null; ........... return File(,,); } When the view is called, function GetFile it just won't work. But if I cut out the parameter int id1 and I instantiate it as a variable it does work. public FileContentResult GetFile() { int idl = 32; SqlDataReader rdr; byte[] fileContent = null; ........... return File(,,); } Why?

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• We say Reference are const pointers. Why I am able to assign a new variable to ref B? The below prog

  - by sandeep

  #include<iostream.h> int main() { int a=10; int &b=a; cout<<"B"<<'\n'<<b; cout<<"A"<<'\n'<<a; b=100; cout<<"B"<<'\n'<<b; cout<<"A"<<'\n'<<a; int c=20; b=c; cout<<"C"<<'\n'<<c; cout<<"B"<<'\n'<<b; }

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• Boost threading/mutexs, why does this work?

  - by Flamewires

  Code: #include <iostream> #include "stdafx.h" #include <boost/thread.hpp> #include <boost/thread/mutex.hpp> using namespace std; boost::mutex mut; double results[10]; void doubler(int x) { //boost::mutex::scoped_lock lck(mut); results[x] = x*2; } int _tmain(int argc, _TCHAR* argv[]) { boost::thread_group thds; for (int x = 10; x>0; x--) { boost::thread *Thread = new boost::thread(&doubler, x); thds.add_thread(Thread); } thds.join_all(); for (int x = 0; x<10; x++) { cout << results[x] << endl; } return 0; } Output: 0 2 4 6 8 10 12 14 16 18 Press any key to continue . . . So...my question is why does this work(as far as i can tell, i ran it about 20 times), producing the above output, even with the locking commented out? I thought the general idea was: in each thread: calculate 2*x copy results to CPU register(s) store calculation in correct part of array copy results back to main(shared) memory I would think that under all but perfect conditions this would result in some part of the results array having 0 values. Is it only copying the required double of the array to a cpu register? Or is it just too short of a calculation to get preempted before it writes the result back to ram? Thanks.

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• How to wrap a C function whose parameters are pointer to structs, so that it can be called from Lua?

  - by pierr

  I have the follwing C function. How should I wrap it so it can be called from a Lua script? typedef struct tagT{ int a ; int b ; } type_t; int lib_a_f_4(type_t *t) { return t->a * t->b ; } I know how to wrapr it if the function parameter type were int or char *. Should I use table type for a C structure? EDIT: I am using SWIG for the wraping , according to this doc, It seems that I should automatically have this funtion new_type_t(2,3) , but it is not the case. If you wrap a C structure, it is also mapped to a Lua userdata. By adding a metatable to the userdata, this provides a very natural interface. For example, struct Point{ int x,y; }; is used as follows: p=example.new_Point() p.x=3 p.y=5 print(p.x,p.y) 3 5 Similar access is provided for unions and the data members of C++ classes. C structures are created using a function new_Point(), but for C++ classes are created using just the name Point().

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• This recursive function puzzles me, what is going on?

  - by Fred

  I was playing around with recursion and did this simple function. I was assuming that it would print out 9-0 to stdout, but, it prints 0-9. I can't see how that happens at all. int main() { rec(10); return 0; } int rec(int n){ if(n > 0) printf("%d\n", rec(n -1)); return n; }

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• In C# why can't a conditional operator implicitly cast to a nullable type

  - by Tim Jarvis

  I am curious as to why an implicit cast fails in... int? someValue = SomeCondition ? ResultOfSomeCalc() : null; and why I have to perform an explicit cast instead int? someValue = SomeCondition ? ResultofSomeCalc() : (int?)null; It seems to me that the compiler has all the information it need to make an implicit casting decision, no?

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• How to check that string is not null or Nan and is less than 108 and greater than 1?

  - by Steven Spielberg

  Do you know how to use int in Javascript? How can I check that a string contains an int or not? How can I check that int is less than 108 and greater than 1?

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• [Netbeans 6.9] Java MethodOverloading error with double values

  - by Nimitips

  Here is a part of my code I'm having trouble with: ===Class Overload=== public class Overload { public void testOverLoadeds() { System.out.printf("Square of integer 7 is %d\n",square(7)); System.out.printf("Square of double 7.5 is %d\n",square(7.5)); }//..end testOverloadeds public int square(int intValue) { System.out. printf("\nCalled square with int argument: %d\n",intValue); return intValue * intValue; }//..end square int public double square(double doubleValue) { System.out.printf("\nCalled square with double argument: %d\n", doubleValue); return doubleValue * doubleValue; }//..end square double }//..end class overload ===Main=== public static void main(String[] args) { Overload methodOverload = new Overload(); methodOverload.testOverLoadeds(); } It compiles with no error, however when I try to run it the output is: Called square with int argument: 7 Square of integer 7 is 49 Exception in thread "main" java.util.IllegalFormatConversionException: d != java.lang.Double at java.util.Formatter$FormatSpecifier.failConversion(Formatter.java:3999) at java.util.Formatter$FormatSpecifier.printInteger(Formatter.java:2709) at java.util.Formatter$FormatSpecifier.print(Formatter.java:2661) at java.util.Formatter.format(Formatter.java:2433) at java.io.PrintStream.format(PrintStream.java:920) at java.io.PrintStream.printf(PrintStream.java:821) at methodoverload.Overload.square(Overload.java:19) at methodoverload.Overload.testOverLoadeds(Overload.java:8) at methodoverload.Main.main(Main.java:9) Called square with double argument:Java Result: 1 What am I doing wrong? I'm on Ubuntu 10.10, Netbeans 6.9. Thanks.

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• GDI+ Resize Function

  - by Tyler

  So my logic is flawed and I need a better and correct way to resize an image in my c# app I need a function similar to this setup public void ResizeImageForWeb(string OriginalFile, string NewFile, int MaxWidth, int MaxHeight, int Quality) { // Resize Code } Basically, I'm a web designer lost trying to programming a desktop app.

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• Optional parameters for interfaces

  - by bryanjonker

  Using c# 4.0 -- building an interface and a class that implements the interface. I want to declare an optional parameter in the interface and have it be reflected in the class. So, I have the following: public interface IFoo { void Bar(int i, int j=0); } public class Foo { void Bar(int i, int j=0) { // do stuff } } This compiles, but it doesn't look right. The interface needs to have the optional parameters, because otherwise it doesn't reflect correctly in the interface method signature. Should I skip the optional parameter and just use a nullable type? Or will this work as intended with no side effects or consequences?

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• Concurrency problem with arrays (Java)

  - by Johannes

  For an algorithm I'm working on I tried to develop a blacklisting mechanism that can blacklist arrays in a specific way: If "1, 2, 3" is blacklisted "1, 2, 3, 4, 5" is also considered blacklisted. I'm quite happy with the solution I've come up with so far. But there seem to be some serious problems when I access a blacklist from multiple threads. The method "contains" (see code below) sometimes returns true, even if an array is not blacklisted. This problem does not occur if I only use one thread, so it most likely is a concurrency problem. I've tried adding some synchronization, but it didn't change anything. I also tried some slightly different implementations using java.util.concurrent classes. Any ideas on how to fix this? public class Blacklist { private static final int ARRAY_GROWTH = 10; private final Node root = new Node(); private static class Node{ private volatile Node[] childNodes = new Node[ARRAY_GROWTH]; private volatile boolean blacklisted = false; public void blacklist(){ this.blacklisted = true; this.childNodes = null; } } public void add(final int[] array){ synchronized (root) { Node currentNode = this.root; for(final int edge : array){ if(currentNode.blacklisted) return; else if(currentNode.childNodes.length <= edge) { currentNode.childNodes = Arrays.copyOf(currentNode.childNodes, edge + ARRAY_GROWTH); } if(currentNode.childNodes[edge] == null) { currentNode.childNodes[edge] = new Node(); } currentNode = currentNode.childNodes[edge]; } currentNode.blacklist(); } } public boolean contains(final int[] array){ synchronized (root) { Node currentNode = this.root; for(final int edge : array){ if(currentNode.blacklisted) return true; else if(currentNode.childNodes.length <= edge || currentNode.childNodes[edge] == null) return false; currentNode = currentNode.childNodes[edge]; } return currentNode.blacklisted; } } }

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• Count seconds and minutes with MCU timer/interrupt?

  - by arynhard

  I am trying to figure out how to create a timer for my C8051F020 MCU. The following code uses the value passed to init_Timer2() with the following formula: 65535-(0.1 / (12/2000000)=48868. I set up the timer to count every time it executes and for every 10 counts, count one second. This is based on the above formula. 48868 when passed to init_Timer2 will produce a 0.1 second delay. It would take ten of them per second. However, when I test the timer it is a little fast. At ten seconds the timer reports 11 seconds, at 20 seconds the timer reports 22 seconds. I would like to get as close to a perfect second as I can. Here is my code: #include <compiler_defs.h> #include <C8051F020_defs.h> void init_Clock(void); void init_Watchdog(void); void init_Ports(void); void init_Timer2(unsigned int counts); void start_Timer2(void); void timer2_ISR(void); unsigned int timer2_Count; unsigned int seconds; unsigned int minutes; int main(void) { init_Clock(); init_Watchdog(); init_Ports(); start_Timer2(); P5 &= 0xFF; while (1); } //============================================================= //Functions //============================================================= void init_Clock(void) { OSCICN = 0x04; //2Mhz //OSCICN = 0x07; //16Mhz } void init_Watchdog(void) { //Disable watchdog timer WDTCN = 0xDE; WDTCN = 0xAD; } void init_Ports(void) { XBR0 = 0x00; XBR1 = 0x00; XBR2 = 0x40; P0 = 0x00; P0MDOUT = 0x00; P5 = 0x00; //Set P5 to 1111 P74OUT = 0x08; //Set P5 4 - 7 (LEDs) to push pull (Output) } void init_Timer2(unsigned int counts) { CKCON = 0x00; //Set all timers to system clock divided by 12 T2CON = 0x00; //Set timer 2 to timer mode RCAP2 = counts; T2 = 0xFFFF; //655535 IE |= 0x20; //Enable timer 2 T2CON |= 0x04; //Start timer 2 } void start_Timer2(void) { EA = 0; init_Timer2(48868); EA = 1; } void timer2_ISR(void) interrupt 5 { T2CON &= ~(0x80); P5 ^= 0xF0; timer2_Count++; if(timer2_Count % 10 == 0) { seconds++; } if(seconds % 60 == 0 && seconds != 0) { minutes++; } }

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• sqlite3 date operations when joining two tables in a view?

  - by duncan

  In short, how to add minutes to a datetime from an integer located in another table, in one select statement, by joining them? I have a table P(int id, ..., int minutes) and a table S(int id, int p_id, datetime start) I want to generate a view that gives me PS(S.id, P.id, S.start + P.minutes) by joining S.p_id=P.id The problem is, if I was generating the query from the application, I can do stuff like: select datetime('2010-04-21 14:00', '+20 minutes'); 2010-04-21 14:20:00 By creating the string '+20 minutes' in the application and then passing it to sqlite. However I can't find a way to create this string in the select itself: select p.*,datetime(s.start_at, formatstring('+%s minutes', p.minutes)) from p,s where s.p_id=p.id; Because sqlite as far the documentation tells, does not provide any string format function, nor can I see any alternative way of expressing the date modifiers.

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• Display a variable when a select box option is selected

  - by user782104

  For example, the select box <select><option selected="" value="">Please Select</option><option value='txt'>Text</option><option value='int'>Numbers</option><option value='bool' >Boolean</option></select> has a string $messageList=array ( 'txt'=>'text message', 'int'=>'int message','bool'=>'bool message'); What i would like to achieve is to display correspond message when the optition is select?

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• Getting tree construction with ANTLR

  - by prosseek

  As asked and answered in http://stackoverflow.com/questions/2999755/removing-left-recursion-in-antlr , I could remove the left recursion E - E + T|T T - T * F|F F - INT | ( E ) After left recursion removal, I get the following one E - TE' E' - null | + TE' T - FT' T' - null | * FT' Then, how to make the tree construction with the modified grammar? With the input 1+2, I want to have a tree ^('+' ^(INT 1) ^(INT 2)). Or similar. grammar T; options { output=AST; language=Python; ASTLabelType=CommonTree; } start : e - e ; e : t ep - ??? ; ep : | '+' t ep - ??? ; t : f tp - ??? ; tp : | '*' f tp - ??? ; f : INT | '(' e ')' - e ; INT : '0'..'9'+ ; WS: (' '|'\n'|'\r')+ {$channel=HIDDEN;} ;

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• C header file won't compile with C, but will with C++.

  - by Leif Andersen

  I have the following chunk of a header file BKE_mesh.h: /* Connectivity data */ typedef struct IndexNode { struct IndexNode *next, *prev; int index; } IndexNode; void create_vert_face_map(ListBase **map, IndexNode **mem, const struct MFace *mface, const int totvert, const int totface); void create_vert_edge_map(ListBase **map, IndexNode **mem, const struct MEdge *medge, const int totvert, const int totedge); Note that the header file was prepared for the possibility of being used in a C++ file, as it had: #ifdef __cplusplus extern "C" { #endif at the top of the file, and the needed finish at the bottom. But the class implementing it was written in C. Next, whenever I try to #include the header file, I get an odd error. If the file has a .cpp extension, it compiles just fine, no complaints whatsoever. However, if I do: #include "BKE_mesh.h" inside of a file with a .c extension, I get the following errors: expected ')' before '*' token for the two last functions, in specific, the variable: ListBase **map in both classes. (Note that earlier in the header file, it declared, but not defined ListBase). So, my question is: why is this valid C++ code, but not C code? Thank you.

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• Generate a commutative hash based on three sets of numbers?

  - by DarkAmgine

  I need to generate a commutative hash based on three sets of "score" structs. Each score has a "start", an "end" and a "number". Both start and end are usually huge numbers (8-9 digits) but number is just from 1 to 4. I need them to be commutative so the order does not matter. I'm using XOR at the moment but it seems to be giving bad results. Since I'm working with large large datasets, I'd prefer a performance-friendly solution. Any suggestions? Thanks =] public static int getCustomHash(cnvRegion c1, cnvRegion c2, cnvRegion c3) { int part1 = (c1.startLocation * c2.startLocation * c3.startLocation); int part2 = (c1.endLocation * c2.endLocation * c3.endLocation); int part3 = (c1.copyNumber + c2.copyNumber + c3.copyNumber)*23735160; return part1 ^ part2 ^ part3; }

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• C++ function-pointer and inheritance

  - by pingvinus

  In parent class I have function, that operates under an array of functions, declared in child-class, number of functions for every child-class may vary. But since every function uses some object-variables, I can't declare them as static. I've try to do something like this: class A { public: typedef int (A::*func)(); func * fs; void f() { /*call functions from this->fs*/ } }; class B : public A { public: int smth; B(int smth) { this->smth = smth; this->fs = new func[1]; fs[0] = &B::f; } int f() { return smth + 1; } }; But, obviously it doesn't work. Any suggestions?

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• "Right" way to deallocate an std::vector object

  - by Jacob

  The first solution is: std::vector<int> *vec = new std::vector<int>; assert(vec != NULL); // ... delete vec; An alternative is: std::vector<int> v; //... vec.clear(); vec.swap(std::vector<int>(vec)); The second solution's a bit of a trick --- what's the "right" way to do it?

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• Rowwise iteration of a dictionay object

  - by mono

  I have a dictionary object like: Dictionary<string, HashSet<int>> dict = new Dictionary<string, HashSet<int>>(); dict.Add("foo", new HashSet<int>() { 15,12,16,18}); dict.Add("boo", new HashSet<int>() { 16,47,45,21 }); I have to print in such a way such that result would be as following at each iteration: It1: foo boo //only the key in a row It2: 15 16 It3: 16 47 Can anyone help me to achieve this. Thanks.

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• a constructor as a delegate - is it possible in C#?

  - by akavel

  I have a class like below: class Foo { public Foo(int x) { ... } } and I need to pass to a certain method a delegate like this: delegate Foo FooGenerator(int x); Is it possible to pass the constructor directly as a FooGenerator value, without having to type: delegate(int x) { return new Foo(x); } ? EDIT: For my personal use, the question refers to .NET 2.0, but hints/responses for 3.0+ are welcome as well.

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• Is it possible to have a function pointer to a template function in c++?

  - by LoudNPossiblyRight

  I want to know if it's possible to create a template function and then create a function pointer that points to that template function. Is this possible? I'm using VS2008, what's wrong with this code? template<typename T> T __cdecl tfunc(const T &x, const T &y){ return (x < y ? x : y); } int (*tfunc_ptr)(int, int) = &tfunc;

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• undefined reference to static member variable

  - by Max

  Hi. I have this class that has a static member. it is also a base class for several other classes in my program. Here's its header file: #ifndef YARL_OBJECT_HPP #define YARL_OBJECT_HPP namespace yarlObject { class YarlObject { // Member Variables private: static int nextID; // keeps track of the next ID number to be used int ID; // the identifier for a specific object // Member Functions public: YarlObject(): ID(++nextID) {} virtual ~YarlObject() {} int getID() const {return ID;} }; } #endif and here's its implementation file. #include "YarlObject.hpp" namespace yarlObject { int YarlObject::nextID = 0; } I'm using g++, and it returns three undefined reference to 'yarlObject::YarlObject::nextID linker errors. If I change the ++nextID phrase in the constructor to just nextID, then I only get one error, and if I change it to 1, then it links correctly. I imagine it's something simple, but what's going on?

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• how to wrapper a c function whose parameters are a point to struct so that it can be called by lua s

  - by pierr

  Hi, I have follwing C function. How should I wrapper it so it can be called by lua script? typedef struct tagT{ int a ; int b ; }type_t; int lib_a_f_4(type_t *t) { return t->a * t->b ; } I know how to wrapper it if the function parameter type were int or char *. Should I use table type for a C structure? I am a lua beginner and thanks for help.

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