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  • PDFParsing & extracting the images only in iPhone application.

    - by sagar
    Hello - Every one. ** : My Query : ** I want to extract only images from entire pdf document. ( Using Objective C - for iPhone Application ) : My Efforts : I have gone through this link which has details regarding different operators of PDF Document. ( http://mail-archives.apache.org/mod_mbox/pdfbox-commits/200912.mbox/%[email protected]%3E ) I also studied this document - ( http://developer.apple.com/mac/library/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_pdf_scan/dq_pdf_scan.html#//apple_ref/doc/uid/TP30001066-CH220-TPXREF101 ) I also have gone through entire document of PDFReference.pdf ( From original Adobe Site ) PDFReference.pdf (Adobe Document - says that - for image there are following operators ) q Q BI EI I have placed following table get the image myTable = CGPDFOperatorTableCreate(); CGPDFOperatorTableSetCallback(myTable, "q", arrayCallback2); CGPDFOperatorTableSetCallback(myTable, "TJ", arrayCallback); CGPDFOperatorTableSetCallback(myTable, "Tj", stringCallback); I have following arrayCallback2 method for getting image void arrayCallback2(CGPDFScannerRef inScanner, void *userInfo) { // how to extract image from this code // means I have tried too many different ways. following is incorrect way & not giving image // CGPDFStreamRef stream; // represents a sequence of bytes // if (CGPDFDictionaryGetStream (d, "BI", &stream)){ // CGPDFDataFormat t=CGPDFDataFormatJPEG2000; // CFDataRef data = CGPDFStreamCopyData (stream, &t); // } } above arrayCallback2 method is called for operator "q", But I don't know How to extract the image from it. In short. What should be the solution for extracting the images from the pdf documents? Thanks in advance for your kind help. Sagar kothari.

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  • How to enforce users to create objects of class derived from mine with "new" only?

    - by sharptooth
    To implement reference counting we use an IUnknown-like interface and a smart pointer template class. The interface has implementation for all the reference-count methods, including Release(): void IUnknownLike::Release() { if( --refCount == 0 ) { delete this; } } The smart pointer template class has a copy constructor and an assignment operator both accepting raw pointers. So users can do the following: class Class : public IUnknownLike { }; void someFunction( CSmartPointer<Class> object ); //whatever function Class object; someFunction( &object ); and the program runs into undefined behavior - the object is created with reference count zero, the smart pointer is constructed and bumps it to one, then the function returns, smart pointer is destroyed, calls Release() which leads to delete of a stack-allocated variable. Users can as well do the following: struct COuter { //whatever else; Class inner;// IUnknownLike descendant }; COuter object; somefunction( &object.Inner ); and again an object not created with new is deleted. Undefined behavior at its best. Is there any way to change the IUnknownLike interface so that the user is forced to use new for creating all objects derived from IUnknownLike - both directly derived and indirectly derived (with classes in between the most derived and the base)?

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  • vector <T *> destructor

    - by Daniel.Z
    I have a class defined like: Class A { public: int num; A *parent; vector<A *> children; ... // constructor without parameters A(void) { this->num = 3; this->parent = 0; for (int i=0;i<num;++i) children.push_back(new A(this,num-1)); } // constructor with parameters A(A *a,int n) { this->num = n; this->children->parent = a; for (int i=0;i<num;++i) this->children.push_back(new A(this,this->num-1)); } }; now, the constructor works fine. there are some problem with destructor. currently, the destructor is defined as: A::~A(void) { if (this->parent!=0) this->parent = 0; for (int i=0;i<(int)children.size();++i) this->children[i]->~A(); vector <A *> ().swap(this->children); } but every time when I debug it, it will break at: void deallocate(pointer _Ptr, size_type) { // deallocate object at _Ptr, ignore size ::operator delete(_Ptr); } it looks like I cannot delete the pointer in the vector of this-children, is there any way that I can de-construct the class successfully?

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  • [C++] My First Go With Function Templates

    - by bobber205
    Thought it was pretty straight forward. But I get a "iterator not dereferencable" errro when running the below code. What's wrong? template<typename T> struct SumsTo : public std::binary_function<T, T, bool> { int myInt; SumsTo(int a) { myInt = a; } bool operator()(const T& l, const T& r) { cout << l << " + " << r; if ((l + r) == myInt) { cout << " does add to " << myInt; } else { cout << " DOES NOT add to " << myInt; } return true; } }; void main() { list<int> l1; l1.push_back(1); l1.push_back(2); l1.push_back(3); l1.push_back(4); list<int> l2; l2.push_back(9); l2.push_back(8); l2.push_back(7); l2.push_back(6); transform(l1.begin(), l1.end(), l2.begin(), l2.end(), SumsTo<int>(10) ); }

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  • How do I send floats in window messages.

    - by yngvedh
    Hi, What is the best way to send a float in a windows message using c++ casting operators? The reason I ask is that the approach which first occurred to me did not work. For the record I'm using the standard win32 function to send messages: PostWindowMessage(UINT nMsg, WPARAM wParam, LPARAM lParam) What does not work: Using static_cast<WPARAM>() does not work since WPARAM is typedef'ed to UINT_PTR and will do a numeric conversion from float to int, effectively truncating the value of the float. Using reinterpret_cast<WPARAM>() does not work since it is meant for use with pointers and fails with a compilation error. I can think of two workarounds at the moment: Using reinterpret_cast in conjunction with the address of operator: float f = 42.0f; ::PostWindowMessage(WM_SOME_MESSAGE, *reinterpret_cast<WPARAM*>(&f), 0); Using an union: union { WPARAM wParam, float f }; f = 42.0f; ::PostWindowMessage(WM_SOME_MESSAGE, wParam, 0); Which of these are preffered? Are there any other more elegant way of accomplishing this?

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  • Why does instanceof seem to work in a static generic function sometimes?

    - by michael
    Greetings. This is my first post in this site. I thought that because of type erasure, one could not expect the following code to compile, and indeed, it did not compile on an earlier version of Eclipse. My understanding was that instanceof was a run-time operator and could not know about the generic type which would be, by run-time, compiled away: public static <E extends Comparable<? super E>> void SampleForQuestion(E e) { if ( !(e instanceof String) ) System.out.println("I am not a String"); else System.out.println("I am a String"); } However, I was surprised to see that one of your threads actually included some code like this in an answer, and my latest Eclipse (Galileo on Windows with JVM 1.6 rev 20) is perfectly happy with it -- and it works, too. (I did notice that someone said it worked on Eclipse but not in another IDE/JDK in that thread, but don't remember the specifics.) Can someone explain why it works, and more importantly, because I have to guide my students, whether it should be expected to work in the future. Thank you. (I hope the code formatting comes through correctly - it looks indented correctly from my perspective and there are no tabs.)

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  • What does it mean to pass a &variable to a function? E.g., string& insert ( size_t pos1, const strin

    - by Bob Montgomery
    I understand passing a pointer, and returning a pointer: char * strcat ( char * destination, const char * source ); You're passing a variable that contains the address to a char; returning the same. But what does it mean to pass something using the reference operator? Or to return it? string& insert ( size_t pos1, const string& str ); I mean, I understand what actually happens, I just don't understand the notation. Why isn't the notation this instead: string * insert ( size_t pos1, const string * str ); //made up I presume it has something to do with passing/returning the instance of a class, but what? Is this syntax valid; if not why not and if so what does it mean? char & strcat ( char & destination, const char & source ); //made up (all of the function declarations, except the last made-up two, are from http://www.cplusplus.com )

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  • How do the operators < and > work with pointers?

    - by Øystein
    Just for fun, I had a std::list of const char*, each element pointing to a null-terminated text string, and ran a std::list::sort() on it. As it happens, it sort of (no pun intended) did not sort the strings. Considering that it was working on pointers, that makes sense. According to the documentation of std::list::sort(), it (by default) uses the operator < between the elements to compare. Forgetting about the list for a moment, my actual question is: How do these (, <, =, <=) operators work on pointers in C++ and C? Do they simply compare the actual memory addresses? char* p1 = (char*) 0xDAB0BC47; char* p2 = (char*) 0xBABEC475; e.g. on a 32-bit, little-endian system, p1 p2 because 0xDAB0BC47 0xBABEC475? Testing seems to confirm this, but I thought it'd be good to put it on StackOverflow for future reference. C and C++ both do some weird things to pointers, so you never really know...

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  • C++ find multiple keys from a std::multimap

    - by sch0ck9
    I have a STL::multimap and I search to populate a std::list with value which key is duplicated. Can I find/insert to a std::list the value of elements for all key where count 1 without counting them one by one? std::multimap<int, std::string> mm ; mm[0] = "a" ; mm[1] = "b" ; mm[0] = "c" ; mm[2] = "j" ; mm[2] = "k" ; std::list<std::string> lst ; lst might contains "a" ,"c","j","k" ; I try this template <class K, class V> class extract_value { private: K last_key_ ; std::list<V> m_list_value ; std::pair<K, V> first_elem ; public: extract_value(const K& k_): last_key_(k_) { } void operator() (std::pair<const K, V> elem) { if (last_key_ == elem.first) { m_list_value.push_back(elem.second) ; } else { // First entry last_key_ = elem.first; first_elem= elem ; } } std::list<V> get_value() { return m_list_value ; } }; ex_ = for_each(mm.begin(),mm.end(), extract_value<int, std::string>(0)) ; std::list<std::string> lst = ex_.get_value() ; I'm not sure that this code compile.

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  • Using an ActiveX control without a form/dialog/window in C++, VS 2008

    - by younevertell
    an ActiveX control generated by Visual Basic 6, very old stuff, it has a couple of methods and one event. now I have to use the control in C++, visual studio 2008, but I don't like to generate a form/dialog/window as constainer. I add some MFC class From ActiveX Control. Now the wrap class has all the methods defined in the ActiveX control. I definitely need add event handler to take care of the event fired by ActiveX control. With a form/dialgue/window, it could be done by below BEGIN_EVENTSINK_MAP ON_EVENT. My questions are 1. how to add the event handler without a form/dialgue/window. Is this impossible? 2. Could I manually add constructor in the ActiveX control wrap class, so I could use new operator to get an instance on the heap? Thanks Add the Event Sinks Map near the start of the definition (.cpp) file. The BEGIN_EVENTSINK_MAP macro takes the container's Class name, then the base class name as parameters. The container's class name is used again in the AFX_EVENTSINK_MAP macro and the ON_EVENT macro.

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  • C++ Matrix class hierachy

    - by bpw1621
    Should a matrix software library have a root class (e.g., MatrixBase) from which more specialized (or more constrained) matrix classes (e.g., SparseMatrix, UpperTriangluarMatrix, etc.) derive? If so, should the derived classes be derived publicly/protectively/privately? If not, should they be composed with a implementation class encapsulating common functionality and be otherwise unrelated? Something else? I was having a conversation about this with a software developer colleague (I am not per se) who mentioned that it is a common programming design mistake to derive a more restricted class from a more general one (e.g., he used the example of how it was not a good idea to derive a Circle class from an Ellipse class as similar to the matrix design issue) even when it is true that a SparseMatrix "IS A" MatrixBase. The interface presented by both the base and derived classes should be the same for basic operations; for specialized operations, a derived class would have additional functionality that might not be possible to implement for an arbitrary MatrixBase object. For example, we can compute the cholesky decomposition only for a PositiveDefiniteMatrix class object; however, multiplication by a scalar should work the same way for both the base and derived classes. Also, even if the underlying data storage implementation differs the operator()(int,int) should work as expected for any type of matrix class. I have started looking at a few open-source matrix libraries and it appears like this is kind of a mixed bag (or maybe I'm looking at a mixed bag of libraries). I am planning on helping out with a refactoring of a math library where this has been a point of contention and I'd like to have opinions (that is unless there really is an objective right answer to this question) as to what design philosophy would be best and what are the pros and cons to any reasonable approach.

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  • How should I properly format this code?

    - by ct2k7
    Hi, I've a small issue here. I am using an if statement with UIAlertView and I have two situations, both result in UIAlertViews. However, in one situation, I want to dismiss just the UIAlertView, the other, I want the UIAlertView to be dismissed and view to return to root view. This code describes is: if([serverOutput isEqualToString:@"login.true"]){ [Alert dismissWithClickedButtonIndex:0 animated:YES]; [UIApplication sharedApplication].networkActivityIndicatorVisible = NO; UIAlertView *success = [[UIAlertView alloc] initWithTitle:@"Success" message:@"The transaction was a success!" delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil]; [success show]; [success release]; } else { UIAlertView *failure = [[UIAlertView alloc] initWithTitle:@"Failure" message:@"The transaction failed. Contact sales operator!" delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil]; [failure show]; [failure release]; } } -(void)alertView: (UIAlertView *)success clickedButtonAtIndex: (NSInteger)buttonIndex{ switch(buttonIndex) { case 0: { [self.navigationController popToRootViewControllerAnimated:YES]; } } } So, in both cases, they follow the above action, but obviously, that's not what I want. Any ideas on what I do here?

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  • Linq2Sql: query - subquery optimisation

    - by Budda
    I have the following query: IList<InfrStadium> stadiums = (from sector in DbContext.sectors where sector.Type=typeValue select new InfrStadium(sector.TeamId) ).ToList(); and InfrStadium class constructor: private InfrStadium(int teamId) { IList<Sector> teamSectors = (from sector in DbContext.sectors where sector.TeamId==teamId select sector) .ToList<>(); ... work with data } Current implementation perform 1+n queries, where n - number of records fetched the 1st time. I want to optimize that. And another one I would love to do using 'group' operator in way like this: IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IEnumerable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } But attempt to launch query causes the following error: Expression of type 'System.Int32' cannot be used for constructor parameter of type 'System.Collections.Generic.IEnumerable`1[InfrStadiumSector]' Question 1: Could you please explain, what is wrong here, I don't understand why 'team_sectors' is applied as 'System.Int32'? I've tried to change query a little (replace IEnumerable with IQueryeable): IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors.AsQueryable()) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IQueryeable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } In this case I've received another but similar error: Expression of type 'System.Int32' cannot be used for parameter of type 'System.Collections.Generic.IEnumerable1[InfrStadiumSector]' of method 'System.Linq.IQueryable1[InfrStadiumSector] AsQueryableInfrStadiumSector' Question 2: Actually, the same question: can't understand at all what is going on here... P.S. I have another to optimize query idea (describe here: Linq2Sql: query optimisation) but I would love to find a solution with 1 request to DB).

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  • Javascript Getting Objects to Fallback to One Another

    - by Ian
    Here's a ugly bit of Javascript it would be nice to find a workaround. Javascript has no classes, and that is a good thing. But it implements fallback between objects in a rather ugly way. The foundational construct should be to have one object that, when a property fails to be found, it falls back to another object. So if we want a to fall back to b we would want to do something like: a = {sun:1}; b = {dock:2}; a.__fallback__ = b; then a.dock == 2; But, Javascript instead provides a new operator and prototypes. So we do the far less elegant: function A(sun) { this.sun = sun; }; A.prototype.dock = 2; a = new A(1); a.dock == 2; But aside from elegance, this is also strictly less powerful, because it means that anything created with A gets the same fallback object. What I would like to do is liberate Javascript from this artificial limitation and have the ability to give any individual object any other individual object as its fallback. That way I could keep the current behavior when it makes sense, but use object-level inheritance when that makes sense. My initial approach is to create a dummy constructor function: function setFallback(from_obj, to_obj) { from_obj.constructor = function () {}; from_obj.constructor.prototype = to_obj; } a = {sun:1}; b = {dock:2}; setFallback(a, b); But unfortunately: a.dock == undefined; Any ideas why this doesn't work, or any solutions for an implementation of setFallback? (I'm running on V8, via node.js, in case this is platform dependent)

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  • Solved: Help with this compile error

    - by Scott
    I just picked up an old project and I'm not sure what the following error could mean. g++ -o BufferedReader.o -c -g -Wall -std=c++0x -I/usr/include/xmms2 -Ijsoncpp/include/json/ -fopenmp -I/usr/include/ImageMagick -I/usr/include/xmms2 -I/usr/include/libvisual-0.4 -D_GNU_SOURCE=1 -D_REENTRANT -I/usr/include/SDL -DQT_CORE_LIB -DQT_GUI_LIB -DQT_SCRIPT_LIB -DQT_SHARED -I/usr/include/QtCore -I/usr/include/QtGui -I/usr/include/QtScript BufferedReader.cpp In file included from BufferedReader.cpp:23: /usr/include/string.h:36:42: error: missing binary operator before token "(" In file included from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/cwchar:47, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/bits/postypes.h:42, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/iosfwd:42, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/ios:39, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/istream:40, from /usr/lib/gcc/i686-redhat-linux/4.4.3/../../../../include/c++/4.4.3/sstream:39, from BufferedReader.cpp:24: At line 24 of BufferedReader.cpp is #include <string.h>. I've tried it with just <string> but get the same thing. Any clue? Here's the snippet of code from string.h /* Tell the caller that we provide correct C++ prototypes. */ #if defined __cplusplus && __GNUC_PREREQ (4, 4) //line 36 # define __CORRECT_ISO_CPP_STRING_H_PROTO #endif Does that mean __GNUC_PREREQ isn't defined? Edit: Changing -Ijsoncpp/include/json/ to Ijsoncpp/include stopped the errors. I noticed I was including <json/json.h>. I'm about to switch to JsonGlib though, which is the reason I pulled the project up again. So it's all good. :)

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  • Combining two data sets and plotting in matlab

    - by bautrey
    I am doing experiments with different operational amplifier circuits and I need to plot my measured results onto a graph. I have two data sets: freq1 = [.1 .2 .5 .7 1 3 4 6 10 20 35 45 60 75 90 100]; %kHz Vo1 = [1.2 1.6 1.2 2 2 2.4 14.8 20.4 26.4 30.4 53.6 68.8 90 114 140 152]; %mV V1 = 19.6; Acm = Vo1/(1000*V1); And: freq2 = [.1 .5 1 30 60 70 85 100]; %kHz Vo1 = [3.96 3.96 3.96 3.84 3.86 3.88 3.88 3.88]; %V V1 = .96; Ad = Vo1/(2*V1); (I would show my plots but apparently I need more reps for that) I need to plot the equation, CMRR vs freq: CMRR = 20*log10(abs(Ad/Acm)); The size of Ad and Acm are different and the frequency points do not match up, but the boundaries of both of these is the same, 100Hz to 100kHz (x-axis). On the line of CMRR, Matlab says that Ad and Acm matrix dimensions do not agree. How I think I would solve this is using freq1 as the x-axis for CMRR and then taking approximated points from Ad according to the value on freq1. Or I could do function approximations of Ad and Acm and then do the divide operator on those. I do not know how I would code up this two ideas. Any other ideas would helpful, especially simpler ones. Thanks

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  • Casting Type array to Generic array?

    - by George R
    The short version of the question - why can't I do this? I'm restricted to .NET 3.5. T[] genericArray; // Obviously T should be float! genericArray = new T[3]{ 1.0f, 2.0f, 0.0f }; // Can't do this either, why the hell not genericArray = new float[3]{ 1.0f, 2.0f, 0.0f }; Longer version - I'm working with the Unity engine here, although that's not important. What is - I'm trying to throw conversion between its fixed Vector2 (2 floats) and Vector3 (3 floats) and my generic Vector< class. I can't cast types directly to a generic array. using UnityEngine; public struct Vector { private readonly T[] _axes; #region Constructors public Vector(int axisCount) { this._axes = new T[axisCount]; } public Vector(T x, T y) { this._axes = new T[2] { x, y }; } public Vector(T x, T y, T z) { this._axes = new T[3]{x, y, z}; } public Vector(Vector2 vector2) { // This doesn't work this._axes = new T[2] { vector2.x, vector2.y }; } public Vector(Vector3 vector3) { // Nor does this this._axes = new T[3] { vector3.x, vector3.y, vector3.z }; } #endregion #region Properties public T this[int i] { get { return _axes[i]; } set { _axes[i] = value; } } public T X { get { return _axes[0];} set { _axes[0] = value; } } public T Y { get { return _axes[1]; } set { _axes[1] = value; } } public T Z { get { return this._axes.Length (Vector2 vector2) { Vector vector = new Vector(vector2); return vector; } public static explicit operator Vector(Vector3 vector3) { Vector vector = new Vector(vector3); return vector; } #endregion }

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  • LINQ to Entites - Left Outer Join - SQL 2000

    - by user255234
    Hi! I'm using Linq to Entities. I have the following query in my code, it includes left outer Join: var surgeonList = (from item in context.T1_STM_Surgeon.Include("T1_STM_SurgeonTitle") .Include("OTER").Include("OSLP") join reptable in context.OSLP on item.Rep equals reptable.SlpCode into surgRepresentative where item.ID == surgeonId select new { ID = item.ID, First = item.First, Last = item.Last, Rep = (surgRepresentative.FirstOrDefault() != null) ? surgRepresentative.FirstOrDefault().SlpName : "N/A", Reg = item.OTER.descript, PrimClinic = item.T1_STM_ClinicalCenter.Name, Titles = item.T1_STM_SurgeonTitle, Phone = item.Phone, Email = item.Email, Address1 = item.Address1, Address2 = item.Address2, City = item.City, State = item.State, Zip = item.Zip, Comments = item.Comments, Active = item.Active, DateEntered = item.DateEntered }) .ToList(); My DEV server has SQL 2008, so the code works just fine. When I moved this code to client's production server - they use SQL 2000, I started getting "Incorrect syntax near '(' ". I've tried changing the ProviderManifestToken to 2000 in my .edmx file, then I started getting "The execution of this query requires the APPLY operator, which is not supported in versions of SQL Server earlier than SQL Server 2005." I tied changing the token to 2005, the "Incorrect syntax near '(' " is back. Can anybody help me to find a workaround for this? Thank you very much in advance!

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  • Coordinating typedefs and structs in std::multiset (C++)

    - by Sarah
    I'm not a professional programmer, so please don't hesitate to state the obvious. My goal is to use a std::multiset container (typedef EventMultiSet) called currentEvents to organize a list of structs, of type Event, and to have members of class Host occasionally add new Event structs to currentEvents. The structs are supposed to be sorted by one of their members, time. I am not sure how much of what I am trying to do is legal; the g++ compiler reports (in "Host.h") "error: 'EventMultiSet' has not been declared." Here's what I'm doing: // Event.h struct Event { public: bool operator < ( const Event & rhs ) const { return ( time < rhs.time ); } double time; int eventID; int hostID; }; // Host.h ... void calcLifeHist( double, EventMultiSet * ); // produces compiler error ... void addEvent( double, int, int, EventMultiSet * ); // produces compiler error // Host.cpp #include "Event.h" ... // main.cpp #include "Event.h" ... typedef std::multiset< Event, std::less< Event > > EventMultiSet; EventMultiSet currentEvents; EventMultiSet * cePtr = &currentEvents; ... Major questions Where should I include the EventMultiSet typedef? Are my EventMultiSet pointers obviously problematic? Is the compare function within my Event struct (in theory) okay? Thank you very much in advance.

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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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  • Is memory allocation in linux non-blocking?

    - by Mark
    I am curious to know if the allocating memory using a default new operator is a non-blocking operation. e.g. struct Node { int a,b; }; ... Node foo = new Node(); If multiple threads tried to create a new Node and if one of them was suspended by the OS in the middle of allocation, would it block other threads from making progress? The reason why I ask is because I had a concurrent data structure that created new nodes. I then modified the algorithm to recycle the nodes. The throughput performance of the two algorithms was virtually identical on a 24 core machine. However, I then created an interference program that ran on all the system cores in order to create as much OS pre-emption as possible. The throughput performance of the algorithm that created new nodes decreased by a factor of 5 relative the the algorithm that recycled nodes. I'm curious to know why this would occur. Thanks. *Edit : pointing me to the code for the c++ memory allocator for linux would be helpful as well. I tried looking before posting this question, but had trouble finding it.

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  • Understanding C++ pointers (when they point to a pointer)

    - by Stephano
    I think I understand references and pointers pretty well. Here is what I (think I) know: int i = 5; //i is a primitive type, the value is 5, i do not know the address. int *ptr; //a pointer to an int. i have no way if knowing the value yet. ptr = &i; //now i have an address for the value of i (called ptr) *ptr = 10; //go get the value stored at ptr and change it to 10 Please feel free to comment or correct these statements. Now I'm trying to make the jump to arrays of pointers. Here is what I do not know: char **char_ptrs = new char *[50]; Node **node_ptrs = new Node *[50]; My understanding is that I have 2 arrays of pointers, one set of pointers to chars and one to nodes. So if I wanted to set the values, I would do something like this: char_ptrs[0] = new char[20]; node_ptrs[0] = new Node; Now I have a pointer, in the 0 position of my array, in each respective array. Again, feel free to comment here if I'm confused. So, what does the ** operator do? Likewise, what is putting a single * next to the instantiation doing (*[50])? (what is that called exactly, instantiation?)

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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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  • How to use a class's type as the type argument for an inherited collection property in C#

    - by Edelweiss Peimann
    I am trying to create a representation of various types of card that inherit from a generic card class and which all contain references to their owning decks. I tried re-declaring them, as suggested here, but it still won't convert to the specific card type. The code I currently have is as such: public class Deck<T> : List<T> where T : Card { void Shuffle() { throw new NotImplementedException("Shuffle not yet implemented."); } } public class Card { public Deck<Card> OwningDeck { get; set; } } public class FooCard : Card { public Deck<FooCard> OwningDeck { get { return (Deck<FooCard>)base.OwningDeck; } set { OwningDeck = value; } } } The compile-time error I am getting: Error 2 Cannot convert type 'Game.Cards.Deck' to 'Game.Cards.Deck' And a warning suggesting I use a new operator to specify that the hiding is intentional. Would doing so be a violation of convention? Is there a better way? My question to stackoverflow is this: Can what I am trying to do be done elegantly in the .NET type system? If so, can some examples be provided?

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  • Template trick to optimize out allocations

    - by anon
    I have: struct DoubleVec { std::vector<double> data; }; DoubleVec operator+(const DoubleVec& lhs, const DoubleVec& rhs) { DoubleVec ans(lhs.size()); for(int i = 0; i < lhs.size(); ++i) { ans[i] = lhs[i]] + rhs[i]; // assume lhs.size() == rhs.size() } return ans; } DoubleVec someFunc(DoubleVec a, DoubleVec b, DoubleVec c, DoubleVec d) { DoubleVec ans = a + b + c + d; } Now, in the above, the "a + b + c + d" will cause the creation of 3 temporary DoubleVec's -- is there a way to optimize this away with some type of template magic ... i.e. to optimize it down to something equivalent to: DoubleVec ans(a.size()); for(int i = 0; i < ans.size(); i++) ans[i] = a[i] + b[i] + c[i] + d[i]; You can assume all DoubleVec's have the same # of elements. The high level idea is to have do some type of templateied magic on "+", which "delays the computation" until the =, at which point it looks into itself, goes hmm ... I'm just adding thes numbers, and syntheizes a[i] + b[i] + c[i] + d[i] ... instead of all the temporaries. Thanks!

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