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  • Please explain some of Paul Graham's points on LISP

    - by kunjaan
    I need some help understanding some of the points from Paul Graham's article http://www.paulgraham.com/diff.html A new concept of variables. In Lisp, all variables are effectively pointers. Values are what have types, not variables, and assigning or binding variables means copying pointers, not what they point to. A symbol type. Symbols differ from strings in that you can test equality by comparing a pointer. A notation for code using trees of symbols. The whole language always available. There is no real distinction between read-time, compile-time, and runtime. You can compile or run code while reading, read or run code while compiling, and read or compile code at runtime. What do these points mean How are they different in languages like C or Java? Do any other languages other than LISP family languages have any of these constructs now?

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  • StackOverflow Exception in Umanaged Dll When Called from Managed DLL

    - by Ngu Soon Hui
    My question is similar to this one here, but there are some difference. I have a fortran dll as the backend, and a C# exe as the front end. I use PInvoke to pass data between them. There are 22 parameters between the C# and the fortran code. And some of them are integer, double, pointers ( C# pointers), array and whatnot. So it's a mix of types. The problem is that for small arrays, the code works fine, however, for large arrays (~10k element size), a stackoverflowexception was thrown right after my code enters into the managed code. Any idea why this is the case, and how to fix this?

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  • IE8 + Jquery ajax call giving parsererror : for json data which seems valid in Firefox

    - by PlanetUnknown
    The ajax call works fine in FF. the data returned is in JSON here is an example from FF firebug - {"noProfiles": "No profiles have been created, lets start now !"} When I try to print the error in IE8 (& in compatibility modes as well), it says "parsererror". But the output seems to be valid JSON. Here is the ajax function call I'm making. Any pointers would be great ! $.ajax({ type: "GET", url: "/get_all_profile_details/", data: "", dataType: "json", beforeSend: function() {alert("before send called");}, success: function(jsonData) { alert("data received"); }, error: function(xhr, txt, err){ alert("xhr: " + xhr + "\n textStatus: " + txt + "\n errorThrown: " + err); } }); The alerts in the error function above give - xhr:<blank> textstatus:parsererror errorThrown: undefined Any pointers would be great ! Note : jquery : 1.3.2

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  • Free Large datasets to experiment with Hadoop

    - by Sundar
    Do you know any large datasets to experiment with Hadoop which is free/low cost? Any pointers/links related is appreciated. Prefernce: Atleast one GB of data. Production log data of webserver. Few of them which I found so far: http://dumps.wikimedia.org/enwiki/20100130/ http://wiki.freebase.com/wiki/Data_dumps http://aws.amazon.com/publicdatasets/ Also can we run our own crawler to gather data from sites e.g. Wikipedia? Any pointers on how to do this is appreciated as well.

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  • Parameter passing become pointer for integer

    - by Kangkan
    I am working on a c/Linux app for a device. I consume a web service (in WCF/c#) and use gSOAP for the same. The issue is that the parameters in the service methods become pointers for simple data types like int, short etc also. I initially used the same service exposed as ASMX web service and the client proxy generated using gSOAP created methods with parameters passed as values. But once the service has been upgraded to WCF, all the parameters became pointers. Can somebody help?

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  • Is there a COM object that just implements IUnknown I can use?

    - by Matt
    For an asynchronous Windows API, I can provide an IUnknown state parameter to associate calls to the API with calls from the callback. It's my understanding that COM guarantees that two IUnknown pointers to the same object will be of the same value. Thus, if I only want to associate API calls with callbacks, IUnknown should be all I need, by comparing the values of the pointers. Is there a stock implementation of IUnknown I can use? Of course it would be trivial to implement myself, but for such a base component of COM, I'm wondering if Windows or ATL provides one I should use instead. Thanks, --Matt

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  • speech bubbles like in comics for iphone

    - by plspl
    I am new to iphone application development. I am building an iphone app where the user needs to be able to add speech bubbles (think comics) over existing images. I have some questions on how to implement this, Have an empty speech bubble image and overlay it over existing image - Do I use a separate UIImage for the speech bubble? Or should I draw the speech bubble myself? Allow the user to move the speech bubble using touch- Any pointers or examples would be great! Also let him resize the speech depending on the amount of text - Any pointers or examples would be great! Finally he should be able to add text to speech bubble - Is there a way to add textbox over an existing image? Thanks,

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  • Patterns for simulating optional "out" parameters in C#?

    - by Jesse McGrew
    I'm translating an API from C to C#, and one of the functions allocates a number of related objects, some of which are optional. The C version accepts several pointer parameters which are used to return integer handles to the objects, and the caller can pass NULL for some of the pointers to avoid allocating those objects: void initialize(int *mainObjPtr, int *subObjPtr, int *anotherSubObjPtr); initialize(&mainObj, &subObj, NULL); For the C# version, the obvious translation would use out parameters instead of pointers: public static void Initialize(out int mainObj, out int subObj, out int anotherSubObj); ... but this leaves no way to indicate which objects are unwanted. Are there any well-known examples of C# APIs doing something similar that I could imitate? If not, any suggestions?

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  • Reverse a singly linked list

    - by Madhan
    I would be wondered if there exists some logic to reverse the linked list using only two pointers. The following is used to reverse the single linked list using three pointers namely p, q, r: struct node { int data; struct node *link; }; void reverse() { struct node *p = first, *q = NULL, *r; while (p != NULL) { r = q; q = p; p = p->link; q->link = r; } q = first; } Is there any other alternate to reverse the linked list? what would be the best logic to reverse a singly linked list, in terms of time complexity?

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  • why does this code crash?

    - by ashish yadav
    why does this code crash? is using strcat illegal on character pointers? #include <stdio.h> #include <string.h> int main() { char *s1 = "Hello, "; char *s2 = "world!"; char *s3 = strcat(s1, s2); printf("%s",s3); return 0; } please give a proper way with referring to both array and pointers.

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  • How does multiple implementing multiple COM interfaces work in C++?

    - by Martin
    I am trying to understand this example code regarding Browser Helper Objects. Inside, the author implements a single class which exposes multiple interfaces (IObjectWithSite, IDispatch). His QueryInterface function performs the following: if(riid == IID_IUnknown) *ppv = static_cast<BHO*>(this); else if(riid == IID_IObjectWithSite) *ppv = static_cast<IObjectWithSite*>(this); else if (riid == IID_IDispatch) *ppv = static_cast<IDispatch*>(this); I have learned that from a C perspective, interface pointers are just pointers to VTables. So I take it to mean that C++ is capable of returning the VTable of any implemented interface using static_cast. Does this mean that a class constructed in this way has a bunch of VTables in memory (IObjectWithSite, IDispatch, etc)? What does C++ do with the name collisions on the different interfaces (they each have a QueryInterface, AddRef and Release function), can I implement different methods for each of these?

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  • Passing objects by reference or not in C#

    - by Piku
    Suppose I have a class like this: public class ThingManager { List<SomeClass> ItemList; public void AddToList (SomeClass Item) { ItemList.Add(Item); } public void ProcessListItems() { // go through list one item at a time, get item from list, // modify item according to class' purpose } } Assume "SomeClass" is a fairly large class containing methods and members that are quite complex (List<s and arrays, for example) and that there may be a large quantity of them, so not copying vast amounts of data around the program is important. Should the "AddToList" method have "ref" in it or not? And why? It's like trying to learn pointers in C all over again ;-) (which is probably why I am getting confused, I'm trying to relate these to pointers. In C it'd be "SomeClass *Item" and a list of "SomeClass *" variables)

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  • What's the performance penalty of weak_ptr?

    - by Kornel Kisielewicz
    I'm currently designing a object structure for a game, and the most natural organization in my case became a tree. Being a great fan of smart pointers I use shared_ptr's exclusively. However, in this case, the children in the tree will need access to it's parent (example -- beings on map need to be able to access map data -- ergo the data of their parents. The direction of owning is of course that a map owns it's beings, so holds shared pointers to them. To access the map data from within a being we however need a pointer to the parent -- the smart pointer way is to use a reference, ergo a weak_ptr. However, I once read that locking a weak_ptr is a expensive operation -- maybe that's not true anymore -- but considering that the weak_ptr will be locked very often, I'm concerned that this design is doomed with poor performance. Hence the question: What is the performance penalty of locking a weak_ptr? How significant is it?

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  • C++ Passing `this` into method by reference

    - by David
    I have a class constructor that expects a reference to another class object to be passed in as an argument. I understand that references are preferable to pointers when no pointer arithmetic will be performed or when a null value will not exist. This is the header declaration of the constructor: class MixerLine { private: MIXERLINE _mixerLine; public: MixerLine(const MixerDevice& const parentMixer, DWORD destinationIndex); ~MixerLine(); } This is the code that calls the constructor (MixerDevice.cpp): void MixerDevice::enumerateLines() { DWORD numLines = getDestinationCount(); for(DWORD i=0;i<numLines;i++) { MixerLine mixerLine( this, i ); // other code here removed } } Compilation of MixerDevice.cpp fails with this error: Error 3 error C2664: 'MixerLine::MixerLine(const MixerDevice &,DWORD)' : cannot convert parameter 1 from 'MixerDevice *const ' to 'const MixerDevice &' But I thought pointer values could be assigned to pointers, e.g. Foo* foo = new Foo(); Foo& bar = foo;

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  • Template function as a template argument

    - by Kos
    I've just got confused how to implement something in a generic way in C++. It's a bit convoluted, so let me explain step by step. Consider such code: void a(int) { // do something } void b(int) { // something else } void function1() { a(123); a(456); } void function2() { b(123); b(456); } void test() { function1(); function2(); } It's easily noticable that function1 and function2 do the same, with the only different part being the internal function. Therefore, I want to make function generic to avoid code redundancy. I can do it using function pointers or templates. Let me choose the latter for now. My thinking is that it's better since the compiler will surely be able to inline the functions - am I correct? Can compilers still inline the calls if they are made via function pointers? This is a side-question. OK, back to the original point... A solution with templates: void a(int) { // do something } void b(int) { // something else } template<void (*param)(int) > void function() { param(123); param(456); } void test() { function<a>(); function<b>(); } All OK. But I'm running into a problem: Can I still do that if a and b are generics themselves? template<typename T> void a(T t) { // do something } template<typename T> void b(T t) { // something else } template< ...param... > // ??? void function() { param<SomeType>(someobj); param<AnotherType>(someotherobj); } void test() { function<a>(); function<b>(); } I know that a template parameter can be one of: a type, a template type, a value of a type. None of those seems to cover my situation. My main question is hence: How do I solve that, i.e. define function() in the last example? (Yes, function pointers seem to be a workaround in this exact case - provided they can also be inlined - but I'm looking for a general solution for this class of problems).

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  • List of functions references

    - by Ockonal
    Hello, I'm using boost::function for making references to the functions. Can I make a list of references? For example: boost::function<bool (Entity &handle)> behaviorRef; And I need in a list of such pointers. For example: std::vector<behaviorRef> listPointers; Of course it's wrong code due to behaviorRef isn't a type. So the question is: how can I store a list of pointers for the function?

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  • Elegant way for a recursive C++ template to do something different with the leaf class?

    - by Costas
    I have a C++ class template that makes an Array of pointers. This also gets typedefed to make Arrays of Arrays and so on: typedef Array<Elem> ElemArray; typedef Array<ElemArray> ElemArrayArray; typedef Array<ElemArrayArray> ElemArrayArrayArray; I would like to be able to set one leaf node from another by copying the pointer so they both refer to the same Elem. But I also want to be able to set one Array (or Array of Arrays etc) from another. In this case I don't want to copy the pointers, I want to keep the arrays seperate and descend into each one until I get to the leaf node, at where I finally copy the pointers. I have code that does this (below). When you set something in an Array it calls a CopyIn method to do the copying. But because this is templated it also has to call the CopyIn method on the leaf class, which means I have to add a dummy method to every leaf class that just returns false. I have also tried adding a flag to the template to tell it whether it contains Arrays or not, and so whether to call the CopyIn method. This works fine - the CopyIn method of the leaf nodes never gets called, but it still has to be there for the compile to work! Is there a better way to do this? #include <stdio.h> class Elem { public: Elem(int v) : mI(v) {} void Print() { printf("%d\n",mI); } bool CopyIn(Elem *v) { return false; } int mI; }; template < typename T > class Array { public: Array(int size) : mB(0), mN(size) { mB = new T* [size]; for (int i=0; i<mN; i++) mB[i] = new T(mN); } ~Array() { for (int i=0; i<mN; i++) delete mB[i]; delete [] mB; } T* Get(int i) { return mB[i]; } void Set(int i, T* v) { if (! mB[i]->CopyIn(v) ) { // its not an array, so copy the pointer mB[i] = v; } } bool CopyIn(Array<T>* v) { for (int i=0; i<mN; i++) { if (v && i < v->mN ) { if ( ! mB[i]->CopyIn( v->mB[i] )) { // its not an array, so copy the pointer mB[i] = v->mB[i]; } } else { mB[i] = 0; } } return true; // we did the copy, no need to copy pointer } void Print() { for (int i=0; i<mN; i++) { printf("[%d] ",i); mB[i]->Print(); } } private: T **mB; int mN; }; typedef Array<Elem> ElemArray; typedef Array<ElemArray> ElemArrayArray; typedef Array<ElemArrayArray> ElemArrayArrayArray; int main () { ElemArrayArrayArray* a = new ElemArrayArrayArray(2); ElemArrayArrayArray* b = new ElemArrayArrayArray(3); // In this case I need to copy the pointer to the Elem into the ElemArrayArray a->Get(0)->Get(0)->Set(0, b->Get(0)->Get(0)->Get(0)); // in this case I need go down through a and b until I get the to Elems // so I can copy the pointers a->Set(1,b->Get(2)); b->Get(0)->Get(0)->Get(0)->mI = 42; // this will also set a[0,0,0] b->Get(2)->Get(1)->Get(1)->mI = 96; // this will also set a[1,1,1] // should be 42,2, 2,2, 3,3, 3,96 a->Print(); }

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  • IE8 + Jquery ajax call giving parsererror from dJango : for json data which seems valid in Firefox

    - by PlanetUnknown
    The ajax call works fine in FF. the data returned is in JSON here is an example from FF firebug - {"noProfiles": "No profiles have been created, lets start now !"} When I try to print the error in IE8 (& in compatibility modes as well), it says "parsererror". But the output seems to be valid JSON. Here is the ajax function call I'm making. Any pointers would be great ! $.ajax({ type: "GET", url: "/get_all_profile_details/", data: "", dataType: "json", beforeSend: function() {alert("before send called");}, success: function(jsonData) { alert("data received"); }, error: function(xhr, txt, err){ alert("xhr: " + xhr + "\n textStatus: " + txt + "\n errorThrown: " + err); } }); The alerts in the error function above give - xhr:<blank> textstatus:parsererror errorThrown: undefined Any pointers would be great ! Note : jquery : 1.3.2

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  • Generic calls to OnResetDevice() and OnLostDevice()

    - by bobobobo
    This is kind of a COM question to do with DirectX. So, both ID3DXSprite and ID3DXFont and a bunch of the other ID3DX* objects require you to call OnLostDevice() when the d3d device is lost AND OnResetDevice() when the device is reset. What I want to do is maintain an array of all ID3DX* objects and simply call OnResetDevice() and OnLostDevice() on each whenever the device is lost or reset. However I can't seem to find a BASE CLASS for the ID3DX* classes... they all seem to COM-ually inherit from IUnknown. Is there a way to do this or do I have to maintain separate arrays of ID3DXFont* pointers, ID3DXSprite* pointers, etc?

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  • Algorithm Question.. Linked List..

    - by AGeek
    Hi, Scenario is as follows:- I want to reverse the direction of the singly linked list, In other words, after the reversal all pointers should now point backwards.. Well the algorithm should take linear time. The solution that i have thought of using another datastructure A Stack.. With the help of which the singly linked list would be easily reversed, with all pointers pointing backwards.. But i am in doubt, that whether the following implementation yeild linear time complexity.. Please comment on this.. And if any other efficient algorithm is in place, then please discuss.. Thanks.

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  • Function template accepting nothing less than a bidirectional iterator or a pointer

    - by san
    I need a function template that accepts two iterators that could be pointers. If the two arguments are random_access iterators I want the return type to be an object of std::iterator<random_access_iterator_tag, ...> type else a std::iterator<bidirectional_iterator_tag, ...> type. I also want the code to refuse compilation if the arguments are neither a bidirectional iterator, nor a pointer. I cannot have dependency on third party libraries e.g. Boost Could you help me with the signature of this function so that it accepts bidirectional iterators as well as pointers, but not say input_iterator, output_iterator, forward_iterators. One partial solution I can think of is the following template<class T> T foo( T iter1, T iter2) { const T tmp1 = reverse_iterator<T>(iter1); const T tmp2 = reverse_iterator<T>(iter2); // do something } The idea is that if it is not bidirectional the compiler will not let me construct a reverse_iterator from it.

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  • Understanding the concept of Inodes

    - by darkie15
    Hi All, I am referring to the link: http://www.tux4u.nl/freedocs/unix/draw/inode.pdf I am confused on parts: 1 12 direct block pointers 2 1 single indirect block pointer 3 1 double indirect block pointer 4 1 triple indirect block pointer Now the diagram says that each pointer is 32/64 bits. [Query]: Why and how are these values inferred? I mean why specifically have only 32 or 64 bit pointers? The diagram says, One data block{8 KB} for each pointer {4 bytes/8 bytes} [Query]: How does this actually work out? i.e. 8*1024 bytes / 8 bytes = 1024 bytes? What is the logic behind having a 8 bytes pointer for 8KB block? Regards, darkie.

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