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  • Need help profiling .NET caching extension method.

    - by rockinthesixstring
    I've got the following extension Public Module CacheExtensions Sub New() End Sub Private sync As New Object() Public Const DefaultCacheExpiration As Integer = 1200 ''# 20 minutes <Extension()> Public Function GetOrStore(Of T)(ByVal cache As Cache, ByVal key As String, ByVal generator As Func(Of T)) As T Return cache.GetOrStore(key, If(generator IsNot Nothing, generator(), Nothing), DefaultCacheExpiration) End Function <Extension()> Public Function GetOrStore(Of T)(ByVal cache As Cache, ByVal key As String, ByVal generator As Func(Of T), ByVal expireInSeconds As Double) As T Return cache.GetOrStore(key, If(generator IsNot Nothing, generator(), Nothing), expireInSeconds) End Function <Extension()> Public Function GetOrStore(Of T)(ByVal cache As Cache, ByVal key As String, ByVal obj As T) As T Return cache.GetOrStore(key, obj, DefaultCacheExpiration) End Function <Extension()> Public Function GetOrStore(Of T)(ByVal cache As Cache, ByVal key As String, ByVal obj As T, ByVal expireInSeconds As Double) As T Dim result = cache(key) If result Is Nothing Then SyncLock sync If result Is Nothing Then result = If(obj IsNot Nothing, obj, Nothing) cache.Insert(key, result, Nothing, DateTime.Now.AddSeconds(expireInSeconds), cache.NoSlidingExpiration) End If End SyncLock End If Return DirectCast(result, T) End Function End Module From here, I'm using the extension is a TagService to get a list of tags Public Function GetTagNames() As List(Of String) Implements Domain.ITagService.GetTags ''# We're not using a dynamic Cache key because the list of TagNames ''# will persist across all users in all regions. Return HttpRuntime.Cache.GetOrStore(Of List(Of String))("TagNamesOnly", Function() _TagRepository.Read().Select(Function(t) t.Name).OrderBy(Function(t) t).ToList()) End Function All of this is pretty much straight forward except when I put a breakpoint on _TagRepository.Read(). The problem is that it is getting called on every request, when I thought that it is only to be called when Result Is Nothing Am I missing something here?

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  • Objective-C ref count and autorelease

    - by turbovince
    Hey guys, suppose the following code: int main (int argc, const char * argv[]) { //[...] Rectangle* myRect = [[Rectangle alloc] init]; Vector2* newOrigin = [[[Vector2 alloc] init] autorelease]; // ref count 1 [newOrigin setX: 50.0f]; [myRect setOrigin: newOrigin]; // ref count 2 [myRect.origin setXY: 25.0f :100.0f]; // ref count goes to 3... why ? [myRect release]; [pool drain]; return 0; } Rectangle's origin is declared as a (retain) synthesized property. Just wondering 2 things: Why does ref count goes to 3 when using the getter accessor of Rectangle's origin? Am I doing something wrong ? With a ref count of 3, I don't understand how this snippet of code cannot leak. Calling release on myRect will make it go down to 2 since I call release on the origin in dealloc(). But then, when does autorelease take effect? Thanks!

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  • [FIXED] Scan file contents into an array of a structure.

    - by ZaZu
    Hello, I have a structure in my program that contains a particular array. I want to scan a random file with numbers and put the contents into that array. This is my code : ( NOTE : This is a sample from a bigger program, so I need the structure and arrays as declared ) The contents of the file are basically : 5 4 3 2 5 3 4 2 #include<stdio.h> #define first 500 #define sec 500 struct trial{ int f; int r; float what[first][sec]; }; int trialtest(trial *test); main(){ trial test; trialtest(&test); } int trialtest(trial *test){ int z,x,i; FILE *fin; fin=fopen("randomfile.txt","r"); for(i=0;i<5;i++){ fscanf(fin,"%5.2f\t",(*test).what[z][x]); } fclose(fin); return 0; } But the problem is, whenever this I run this code, I get this error : (25) : warning 508 - Data of type 'double' supplied where a pointer is required I tried adding do{ for(i=0;i<5;i++){ q=fscanf(fin,"%5.2f\t",(*test).what[z][x]); } }while(q!=EOF); But that didnt work either, it gives the same error. Does anyone have a solution to this problem ?

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  • an algorhithm for filtering out raw txt files

    - by Roman Luštrik
    Imagine you have a .txt file of the following structure: >>> header >>> header >>> header K L M 200 0.1 1 201 0.8 1 202 0.01 3 ... 800 0.4 2 >>> end of file 50 0.1 1 75 0.78 5 ... I would like to read all the data except lines denoted by >>> and lines below the >>> end of file line. So far I've solved this using read.table(comment.char = ">", skip = x, nrow = y) (x and y are currently fixed). This reads the data between the header and >>> end of file. However, I would like to make my function a bit more plastic regarding the number of rows. Data may have values larger than 800, and consequently more rows. I could scan or readLines the file and see which row corresponds to the >>> end of file and calculate the number of lines to be read. What approach would you use?

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  • C++ program crashes at runtime

    - by qwerty
    Hello, I have this simple c++ program #include <cstdlib> #include <iostream> #include <math.h> #include <stdlib.h> #include <time.h> #include <vector> using namespace std; int aleator(int n) { return (rand()%n)+1; } int main() { int r; int indexes[100]={0}; // const int size=100; //int a[size]; std::vector<int>v; srand(time(0)); for (int i=0;i<25;i++) { int index = aleator(100); if (indexes[index] != 0) { // try again i--; continue; } indexes[index] = 1; cout << v[index] ; } cout<<" "<<endl; system("pause"); return 0; } But at runtime it crashes, so i got that error with 'Send error report' and 'Don't send'. What i'm doing wrong? Thanks!

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  • OpenSceneGraph C++ Access Violation reading location 0x00421000

    - by Kobojunkie
    Working with OpenSceneGraph, and I keep running into this violation issue that I would appreciate some help with. The problem is with the particular line below which happens to be the first in my main function. osg::ref_ptr<osg::Node> bench = osgDB::readNodeFile("Models/test.IVE"); I have my models folder right in my directory. The error is as below. Unhandled exception at 0x68630A6C (msvcr100.dll) in OSG3D.exe: 0xC0000005: Access violation reading location 0x00421000. And this is where the problem seems to be coming up. /** Read an osg::Node from file. * Return valid osg::Node on success, * return NULL on failure. * The osgDB::Registry is used to load the appropriate ReaderWriter plugin * for the filename extension, and this plugin then handles the request * to read the specified file.*/ inline osg::Node* readNodeFile(const std::string& filename) { return readNodeFile(filename,Registry::instance()->getOptions()); } I would appreciate details on how best to tackle this kind of exception message in the future. Are there tools that make this easy to debug or are there ways to capture the exact issues and fix them? I would appreciate any help with this. My ultimate goal is to learn how to better debug C++ related issues please. With this, it means reading through the compiler error list http://msdn.microsoft.com/en-us/library/850cstw1(v=vs.71).aspx is not enough

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  • iPhone - Using sql database - insert statement failing

    - by Satyam svv
    Hi, I'm using sqlite database in my iphone app. I've a table which has 3 integer columns. I'm using following code to write to that database table. -(BOOL)insertTestResult { NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString* documentsDirectory = [paths objectAtIndex:0]; NSString* dataBasePath = [documentsDirectory stringByAppendingPathComponent:@"test21.sqlite3"]; BOOL success = NO; sqlite3* database = 0; if(sqlite3_open([dataBasePath UTF8String], &database) == SQLITE_OK) { BOOL res = (insertResultStatement == nil) ? createStatement(insertResult, &insertResultStatement, database) : YES; if(res) { int i = 1; sqlite3_bind_int(insertResultStatement, 0, i); sqlite3_bind_int(insertResultStatement, 1, i); sqlite3_bind_int(insertResultStatement, 2, i); int err = sqlite3_step(insertResultStatement); if(SQLITE_ERROR == err) { NSAssert1(0, @"Error while inserting Result. '%s'", sqlite3_errmsg(database)); success = NO; } else { success = YES; } sqlite3_finalize(insertResultStatement); insertResultStatement = nil; } } sqlite3_close(database); return success;} The command sqlite3_step is always giving err as 19. I'm not able to understand where's the issue. Tables are created using following queries: CREATE TABLE [Patient] (PID integer NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,PFirstName text NOT NULL,PLastName text,PSex text NOT NULL,PDOB text NOT NULL,PEducation text NOT NULL,PHandedness text,PType text) CREATE TABLE PatientResult(PID INTEGER,PFreeScore INTEGER NOT NULL,PForcedScore INTEGER NOT NULL,FOREIGN KEY (PID) REFERENCES Patient(PID)) I've only one entry in Patient table with PID = 1 BOOL createStatement(const char* query, sqlite3_stmt** stmt, sqlite3* database){ BOOL res = (sqlite3_prepare_v2(database, query, -1, stmt, NULL) == SQLITE_OK); if(!res) NSLog( @"Error while creating %s => '%s'", query, sqlite3_errmsg(database)); return res;}

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  • Strange compilation error on reference passing argument to function

    - by Grewdrewgoo Goobergabbsoen
    Here's the code: #include <iostream> using namespace std; void mysize(int &size, int size2); int main() { int *p; int val; p = &val; cout << p; mysize(&val, 20); // Error is pointed here! } void mysize(int &size, int size2) { cout << sizeof(size); size2 = size2 + 6000; cout << size2; } Here's the error output from GCC: In function 'int main()': Line 10: error: invalid initialization of non-const reference of type 'int&' from a temporary of type 'int*' compilation terminated due to -Wfatal-errors. What does that imply? I do not understand the error message ... invalid initialization of a non-constant? I declared the prototype function above with two parameters to take, one a reference of an integer and one just an integer value itself. I passed the reference of the int (see line 10), yet this error keeps being thrown at me. What is the issue?

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  • Why does this code leak? (simple codesnippet)

    - by Ela782
    Visual Studio shows me several leaks (a few hundred lines), in total more than a few MB. I traced it down to the following "helloWorld example". The leak disappears if I comment out the H5::DataSet.getSpace() line. #include "stdafx.h" #include <iostream> #include "cpp/H5Cpp.h" int main(int argc, char *argv[]) { _CrtSetDbgFlag ( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF ); // dump leaks at return H5::H5File myfile; try { myfile = H5::H5File("C:\\Users\\yyy\\myfile.h5", H5F_ACC_RDONLY); } catch (H5::Exception& e) { std::string msg( std::string( "Could not open HDF5 file.\n" ) + e.getCDetailMsg() ); throw msg; } H5::Group myGroup = myfile.openGroup("/so/me/group"); H5::DataSet myDS = myGroup.openDataSet("./myfloatvec"); hsize_t dims[1]; //myDS.getSpace().getSimpleExtentDims(dims, NULL); // <-- here's the leak H5::DataSpace dsp = myDS.getSpace(); // The H5::DataSpace seems to leak dsp.getSimpleExtentDims(dims, NULL); //dsp.close(); // <-- doesn't help either std::cout << "Dims: " << dims[0] << std::endl; // <-- Works as expected return 0; } Any help would be appreciated. I've been on this for hours, I hate unclean code...

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  • C++ CRTP(template pattern) question

    - by aaa
    following piece of code does not compile, the problem is in T::rank not be inaccessible (I think) or uninitialized in parent template. Can you tell me exactly what the problem is? is passing rank explicitly the only way? or is there a way to query tensor class directly? Thank you #include <boost/utility/enable_if.hpp> template<class T, // size_t N, class enable = void> struct tensor_operator; // template<class T, size_t N> template<class T> struct tensor_operator<T, typename boost::enable_if_c< T::rank == 4>::type > { tensor_operator(T &tensor) : tensor_(tensor) {} T& operator()(int i,int j,int k,int l) { return tensor_.layout.element_at(i, j, k, l); } T &tensor_; }; template<size_t N, typename T = double> // struct tensor : tensor_operator<tensor<N,T>, N> { struct tensor : tensor_operator<tensor<N,T> > { static const size_t rank = N; }; I know the workaround, however am interested in mechanics of template instantiation for self-education

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  • Getting functions of inherited functions to be called

    - by wrongusername
    Let's say I have a base class Animal from which a class Cow inherits, and a Barn class containing an Animal vector, and let's say the Animal class has a virtual function scream(), which Cow overrides. With the following code: Animal.h #ifndef _ANIMAL_H #define _ANIMAL_H #include <iostream> using namespace std; class Animal { public: Animal() {}; virtual void scream() {cout << "aaaAAAAAAAAAAGHHHHHHHHHH!!! ahhh..." << endl;} }; #endif /* _ANIMAL_H */ Cow.h #ifndef _COW_H #define _COW_H #include "Animal.h" class Cow: public Animal { public: Cow() {} void scream() {cout << "MOOooooOOOOOOOO!!!" << endl;} }; #endif /* _COW_H */ Barn.h #ifndef _BARN_H #define _BARN_H #include "Animal.h" #include <vector> class Barn { std::vector<Animal> animals; public: Barn() {} void insertAnimal(Animal animal) {animals.push_back(animal);} void tortureAnimals() { for(int a = 0; a < animals.size(); a++) animals[a].scream(); } }; #endif /* _BARN_H */ and finally main.cpp #include <stdlib.h> #include "Barn.h" #include "Cow.h" #include "Chicken.h" /* * */ int main(int argc, char** argv) { Barn barn; barn.insertAnimal(Cow()); barn.tortureAnimals(); return (EXIT_SUCCESS); } I get this output: aaaAAAAAAAAAAGHHHHHHHHHH!!! ahhh... How should I code this to get MOOooooOOOOOOOO!!! (and whatever other classes inheriting Animal wants scream() to be) instead?

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  • C++ socket protocol design issue (ring inclusion)

    - by Martin Lauridsen
    So I have these two classes, mpqs_client and client_protocol. The mpqs_client class handles a Boost socket connection to a server (sending and receiving messages with some specific format. Upon receiving a message, it calls a static method, parse_message(..), in the class client_protocol, and this method should analyse the message received and perform some corresponding action. Given some specific input, the parse_message method needs to send some data back to the server. As mentioned, this happens through the class mpqs_client. So I could, from mpqs_client, pass "this" to parse_message(..) in client_protocol. However, this leads to a two-way association relationship between the two classes. Something which I reckon is not desireable. Also, to implement this, I would need to include the other in each one, and this gives me a terrible pain. I am thinking this is more of a design issue. What is the best solution here? Code is posted below. Class mpqs_client: #include "mpqs_client.h" mpqs_client::mpqs_client(boost::asio::io_service& io_service, tcp::resolver::iterator endpoint_iterator) : io_service_(io_service), socket_(io_service) { ... } ... void mpqs_client::write(const network_message& msg) { io_service_.post(boost::bind(&mpqs_client::do_write, this, msg)); } Class client_protocol: #include "../network_message.hpp" #include "../protocol_consts.h" class client_protocol { public: static void parse_message(network_message& msg, mpqs_sieve **instance_, mpqs_client &client_) { ... switch (type) { case MPQS_DATA: ... break; case POLYNOMIAL_DATA: ... break; default: break; } }

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  • How to cast C struct just another struct type if their memory size are equal?

    - by Eonil
    I have 2 matrix structs means equal data but have different form like these: // Matrix type 1. typedef float Scalar; typedef struct { Scalar e[4]; } Vector; typedef struct { Vector e[4]; } Matrix; // Matrix type 2 (you may know this if you're iPhone developer) struct CATransform3D { CGFloat m11, m12, m13, m14; CGFloat m21, m22, m23, m24; CGFloat m31, m32, m33, m34; CGFloat m41, m42, m43, m44; }; typedef struct CATransform3D CATransform3D; Their memory size are equal. So I believe there is a way to convert these types without any pointer operations or copy like this: // Implemented from external lib. CATransform3D CATransform3DMakeScale (CGFloat sx, CGFloat sy, CGFloat sz); Matrix m = (Matrix)CATransform3DMakeScale ( 1, 2, 3 ); Is this possible? Currently compiler prints an "error: conversion to non-scalar type requested" message.

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  • How can I hardcode input with the "select" system call in C?

    - by Archer
    If I understand this system call "select" correctly, it will loop waiting for user input from the keyboard or from an outside server. Every time I call "message_loop", I'm going to type in the same few lines of input each time. Is there a way to hard code this in so I don't have to type it in each time? void message_loop(FILE* fpin, FILE* fpout, Socket sock) { fd_set readfds, readfds_bak ; int in, max_fd, n, ret ; char buf[MAXMESG]; in = fileno(fpin) ; FD_ZERO(&readfds) ; FD_SET(in, &readfds) ; FD_SET(sock.socketfd, &readfds) ; readfds_bak = readfds ; max_fd = ((in > sock.socketfd) ? in : sock.socketfd) + 1 ; while(1){ readfds = readfds_bak ; /* select function */ if((ret = select(max_fd, &readfds, NULL, NULL, NULL)) < 0){ perror("select") ; break ; } else if (ret != 0) { if(FD_ISSET(in, &readfds)){ /* keyboard input */ fgets(buf, MAXMESG, fpin) ; if(send_message(buf, sock) == -1) break ; } if(FD_ISSET(sock.socketfd, &readfds)){ /* messages from server */ n = receive_message(buf, MAXMESG, &sock) ; if(n == -1) break ; else if(n > 0){ fputs(buf, fpout) ; fputc('\n', fpout) ; } fflush(stdout) ; } } } }

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  • Are C++ exceptions sufficient to implement thread-local storage?

    - by Potatoswatter
    I was commenting on an answer that thread-local storage is nice and recalled another informative discussion about exceptions where I supposed The only special thing about the execution environment within the throw block is that the exception object is referenced by rethrow. Putting two and two together, wouldn't executing an entire thread inside a function-catch-block of its main function imbue it with thread-local storage? It seems to work fine: #include <iostream> #include <pthread.h> using namespace std; struct thlocal { string name; thlocal( string const &n ) : name(n) {} }; thlocal &get_thread() { try { throw; } catch( thlocal &local ) { return local; } } void print_thread() { cerr << get_thread().name << endl; } void *kid( void *local_v ) try { thlocal &local = * static_cast< thlocal * >( local_v ); throw local; } catch( thlocal & ) { print_thread(); return NULL; } int main() try { thlocal local( "main" ); throw local; } catch( thlocal & ) { print_thread(); pthread_t th; thlocal kid_local( "kid" ); pthread_create( &th, NULL, &kid, &kid_local ); pthread_join( th, NULL ); print_thread(); return 0; } Is this novel or well-characterized? Was my initial premise correct? What kind of overhead does get_thread incur in, say, GCC and VC++? It would require throwing only exceptions derived from struct thlocal, but altogether this doesn't feel like an unproductive insomnia-ridden Sunday morning…

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  • Simple binary File I/O problem with cstdio(c++)

    - by Atilla Filiz
    The c++ program below fails to read the file. I know using cstdio is not good practice but that what I am used to and it should work anyway. $ ls -l l.uyvy -rw-r--r-- 1 atilla atilla 614400 2010-04-24 18:11 l.uyvy $ ./a.out l.uyvy Read 0 bytes out of 614400, possibly wrong file code: #include<cstdio> int main(int argc, char* argv[]) { FILE *fp; if(argc<2) { printf("usage: %s <input>\n",argv[0]); return 1; } fp=fopen(argv[1],"rb"); if(!fp) { printf("erör, cannot open %s for reading\n",argv[1]); return -1; } int bytes_read=fread(imgdata,1,2*IMAGE_SIZE,fp); //2bytes per pixel fclose(fp); if(bytes_read < 2*IMAGE_SIZE) { printf("Read %d bytes out of %d, possibly wrong file\n", bytes_read, 2*IMAGE_SIZE); return -1; } return 0; }

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  • C++ Suppress Automatic Initialization and Destruction

    - by Travis G
    How does one suppress the automatic initialization and destruction of a type? While it is wonderful that T buffer[100] automatically initializes all the elements of buffer, and destroys them when they fall out of scope, this is not the behavior I want. #include <iostream> static int created = 0, destroyed = 0; struct S { S() { ++created; } ~S() { ++destroyed; } }; template <typename T, size_t KCount> class Array { private: T m_buffer[KCount]; public: Array() { // some way to suppress the automatic initialization of m_buffer } ~Array() { // some way to suppress the automatic destruction of m_buffer } }; int main() { { Array<S, 100> arr; } std::cout << "Created:\t" << created << std::endl; std::cout << "Destroyed:\t" << destroyed << std::endl; return 0; } The output of this program is: Created: 100 Destroyed: 100 I would like it to be: Created: 0 Destroyed: 0 My only idea is to make m_buffer some trivially constructed and destructed type like char and then rely on operator[] to wrap the pointer math for me, although this seems like a horribly hacked solution. Another solution would be to use malloc and free, but that gives a level of indirection that I do not want.

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  • Advice: Python Framework Server/Worker Queue management (not Website)

    - by Muppet Geoff
    I am looking for some advice/opinions of which Python Framework to use in an implementation of multiple 'Worker' PCs co-ordinated from a central Queue Manager. For completeness, the 'Worker' PCs will be running Audio Conversion routines (which I do not need advice on, and have standalone code that works). The Audio conversion takes a long time, and I need to co-ordinate an arbitrary number of the 'Workers' from a central location, handing them conversion tasks (such as where to get the source files, or where to ask for the job configuration) with them reporting back some additional info, such as the runtime of the converted audio etc. At present, I have a script that makes a webservice call to get the 'configuration' for a conversion task, based on source files located on the worker already (we manually copy the source files to the worker, and that triggers a conversion routine). I want to change this, so that we can distribute conversion tasks ("Oy you, process this: xxx") based on availability, and in an ideal world, based on pending tasks too. There is a chance that Workers can go offline mid-conversion (but this is not likely). All the workers are Windows based, the co-ordinator can be WIndows or Linux. I have (in my initial searches) come across the following - and I know that some are cross-dependent: Celery (with RabbitMQ) Twisted Django Using a framework, rather than home-brewing, seems to make more sense to me right now. I have a limited timeframe in which to develop this functional extension. An additional consideration would be using a Framework that is compatible with PyQT/PySide so that I can write a simple UI to display Queue status etc. I appreciate that the specifics above are a little vague, and I hope that someone can offer me a pointer or two. Again: I am looking for general advice on which Python framework to investigate further, for developing a Server/Worker 'Queue management' solution, for non-web activities (this is why DJango didn't seem the right fit).

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  • C++ design related question

    - by Kotti
    Hi! Here is the question's plot: suppose I have some abstract classes for objects, let's call it Object. It's definition would include 2D position and dimensions. Let it also have some virtual void Render(Backend& backend) const = 0 method used for rendering. Now I specialize my inheritance tree and add Rectangle and Ellipse class. Guess they won't have their own properties, but they will have their own virtual void Render method. Let's say I implemented these methods, so that Render for Rectangle actually draws some rectangle, and the same for ellipse. Now, I add some object called Plane, which is defined as class Plane : public Rectangle and has a private member of std::vector<Object*> plane_objects; Right after that I add a method to add some object to my plane. And here comes the question. If I design this method as void AddObject(Object& object) I would face trouble like I won't be able to call virtual functions, because I would have to do something like plane_objects.push_back(new Object(object)); and this should be push_back(new Rectangle(object)) for rectangles and new Circle(...) for circles. If I implement this method as void AddObject(Object* object), it looks good, but then somewhere else this means making call like plane.AddObject(new Rectangle(params)); and this is generally a mess because then it's not clear which part of my program should free the allocated memory. ["when destroying the plane? why? are we sure that calls to AddObject were only done as AddObject(new something).] I guess the problems caused by using the second approach could be solved using smart pointers, but I am sure there have to be something better. Any ideas?

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  • Scanning, Checking, Converting, Copying values ... How to ? -- C --

    - by ZaZu
    Hi there, Its been a while now and im still trying to get a certain code to work. I asked some question about different commands etc. before, but now I hope this is the final one (combining all questions in one code). I basically want to : *Scan an input (should be character ? ) *Check if its a number *If not, return error *Convert that character into a float number *Copy the value to another variable ( I called it imp here) Here is what I came up with : #include<stdio.h> #include<stdlib.h> #include<ctype.h> main(){ int digits; float imp=0; int alpha; do{ printf("Enter input\n\n"); scanf("\n%c",&alpha); digits=isdigit(alpha); if(digits==0){ printf("error\n\n"); } imp=atof(alpha); }while(digits==0); } The problem is this code does not work at all ... It gives me that atof must be of a const char and whenever I try changing it around, it just keeps failing. I am frustrated and forced to ask here, because I believe I have tried alot and I keep failing, but I wont be relieved until I get it to work xD So I really need your help guys. Please tell me why isnt this code working, what am I doing wrong ? I am still learning C and really appreciate your help :)

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  • C struct written in file, open with Java

    - by DaunnC
    For example in C I have structure: typedef struct { int number; double x1; double y1; double x2; double y2; double x3; double y3; } CTRstruct;` Then I write it to file fwrite(&tr, 1, sizeof(tr), fp); (tr - its CTRstruct var, fp - File pointer); Then I need to read it with Java! I really don't know how to read struct from file... I tried to read it with ObjectInputStream(), last idea is to read with RandomAccessFile() but I also don't know how to... (readLong(), readDouble() also doesn't work, it works ofcource but doesn't read correct data). So, any idea how to read C struct from binary file with Java? If it's interesting, my version to read integer (but it's ugly, & I don't know what to do with double): public class MyDataInputStream extends DataInputStream{ public MyDataInputStream(InputStream AIs) { super(AIs); } public int readInt1() throws IOException{ int ch1 = in.read(); int ch2 = in.read(); int ch3 = in.read(); int ch4 = in.read(); if ((ch1 | ch2 | ch3 | ch4) < 0) throw new EOFException(); return ((ch4 << 24) + (ch3 << 16) + (ch2 << 8) + (ch1 << 0)); } with double we can deal the same way (like with int or with long (8bytes) & then convert to double with native func).

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  • Changing type of object in a conditional

    - by David Doria
    I'm having a bit of trouble with dynamic_casting. I need to determine at runtime the type of an object. Here is a demo: include include class PersonClass { public: std::string Name; virtual void test(){}; //it is annoying that this has to be here... }; class LawyerClass : public PersonClass { public: void GoToCourt(){}; }; class DoctorClass : public PersonClass { public: void GoToSurgery(){}; }; int main(int argc, char *argv[]) { PersonClass* person = new PersonClass; if(true) { person = dynamic_cast(person); } else { person = dynamic_cast(person); } person-GoToCourt(); return 0; } I would like to do the above. The only legal way I found to do it is to define all of the objects before hand: PersonClass* person = new PersonClass; LawyerClass* lawyer; DoctorClass* doctor; if(true) { lawyer = dynamic_cast(person); } else { doctor = dynamic_cast(person); } if(true) { lawyer-GoToCourt(); } The main problem with this (besides having to define a bunch of objects that won't be use) is that I have to change the name of the 'person' variable. Is there a better way? (I am not allowed to change any of the classes (Person, Lawyer, or Doctor) because they are part of a library that people who will use my code have and won't want to change). Thanks, Dave

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  • How is the C++ synthesized move constructor affected by volatile and virtual members?

    - by user1827766
    Look at the following code: struct node { node(); //node(const node&); //#1 //node(node&&); //#2 virtual //#3 ~node (); node* volatile //#4 next; }; main() { node m(node()); //#5 node n=node(); //#6 } When compiled with gcc-4.6.1 it produces the following error: g++ -g --std=c++0x -c -o node.o node.cc node.cc: In constructor node::node(node&&): node.cc:3:8: error: expression node::next has side-effects node.cc: In function int main(): node.cc:18:14: note: synthesized method node::node(node&&) first required here As I understand the compiler fails to create default move or copy constructor on line #6, if I uncomment either line #1 or #2 it compiles fine, that is clear. The code compiles fine without c++0x option, so the error is related to default move constructor. However, what in the node class prevents default move constructor to be created? If I comment any of the lines #3 or #4 (i.e. make the destructor non-virtual or make data member non-volatile) it compiles again, so is it the combination of these two makes it not to compile? Another puzzle, line #5 does not cause an compilation error, what is different from line #6? Is it all specific for gcc? or gcc-4.6.1?

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  • C Programming. How to deep copy a struct?

    - by user69514
    I have the following two structs where "child struct" has a "rusage struct" as an element. Then I create two structs of type "child" let's call them childA and childB How do I copy just the rusage struct from childA to childB? typedef struct{ int numb; char *name; pid_t pid; long userT; long systemT; struct rusage usage; }child; typedef struct{ struct timeval ru_utime; /* user time used */ struct timeval ru_stime; /* system time used */ long ru_maxrss; /* maximum resident set size */ long ru_ixrss; /* integral shared memory size */ long ru_idrss; /* integral unshared data size */ long ru_isrss; /* integral unshared stack size */ long ru_minflt; /* page reclaims */ long ru_majflt; /* page faults */ long ru_nswap; /* swaps */ long ru_inblock; /* block input operations */ long ru_oublock; /* block output operations */ long ru_msgsnd; /* messages sent */ long ru_msgrcv; /* messages received */ long ru_nsignals; /* signals received */ long ru_nvcsw; /* voluntary context switches */ long ru_nivcsw; /* involuntary context switches */ }rusage; I did the following, but I guess it copies the memory location, because if I changed the value of usage in childA, it also changes in childB. memcpy(&childA,&childB, sizeof(rusage)); I know that gives childB all the values from childA. I have already taken care of the others fields in childB, I just need to be able to copy the rusage struct called usage that resides in the "child" struct.

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  • How to optimize paging for large in memory database

    - by snakefoot
    I have an application where the entire database is implemented in memory using a stl-map for each table in the database. Each item in the stl-map is a complex object with references to other items in the other stl-maps. The application works with a large amount of data, so it uses more than 500 MByte RAM. Clients are able to contact the application and get a filtered version of the entire database. This is done by running through the entire database, and finding items relevant for the client. When the application have been running for an hour or so, then Windows 2003 SP2 starts to page out parts of the RAM for the application (Eventhough there is 16 GByte RAM on the machine). After the application have been partly paged out then a client logon takes a long time (10 mins) because it now generates a page fault for each pointer lookup in the stl-map. I can see it is possible to tell Windows to lock memory in RAM, but this is generally only recommended for device drivers, and only for "small" amounts of memory. I guess a poor mans solution could be to loop through the entire memory database, and thus tell Windows we are still interested in keeping the datamodel in RAM. I guess another poor mans solution could be to disable the pagefile completely on Windows. I guess the expensive solution would be a SQL database, and then rewrite the entire application to use a database layer. Then hopefully the database system will have implemented means to for fast access. Are there other more elegant solutions ?

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