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• Set argument pointer to point to new memory inside a function (without returning it) IN C

  - by user321605

  Hello, Hopefully my title was descriptive enough to attract the right help. I want to write a function that will return 1 thing, and modify a provided pointer in another. My current function declaration is . . . char * afterURL replaceURLS(char * body) What I want to do is copy all of body's data into a new string, and set body to point to this new data. I then want afterURL to point to a location within the new string. My issue is getting the actual pointer that is passed in to this function to point to the new data. Thanks in advance! Rob

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• Reading function pointer syntax

  - by bobobobo

  Everytime I look at a C function pointer, my eyes glaze over. I can't read them. From here, here are 2 examples of function pointer TYPEDEFS: typedef int (*AddFunc)(int,int); typedef void (*FunctionFunc)(); Now I'm used to something like: typedef vector<int> VectorOfInts ; Which I read as typedef vector<int> /* as */ VectorOfInts ; But I can't read the above 2 typedefs. The bracketing and the asterisk placement, it's just not logical. Why is the * beside the word AddFunc..?

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• pointer and malloc [closed]

  - by gcc

  How many methods/ways are there taking input by using with pointer and dynamic memory? Input: 3 1 2 n k l 2 1 2 p 4 55 62 * # x (x is stop value, first input always integer) Example code: p=malloc(sizeof(int)); scanf("%d",&num_arrays); while(1) { scanf("%c",&(*(p+i))); if(*(p+i)=='x') break; ++i; } "3" is stored in num_arrays. The other input values are stored in pointer[array].

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• how to copy an array into somewhere else in the memory by using the pointer

  - by user2758510

  I am completely new in c++ programming. I want to copy the array called distances into where pointer is pointing to and then I want to print out the resul to see if it is worked or not. this is what I have done: int distances[4][6]={{1,0,0,0,1,0},{1,1,0,0,1,1},{1,0,0,0,0,0},{1,1,0,1,0,0}}; int *ptr; ptr = new int[sizeof(distances[0])]; for(int i=0; i<sizeof(distances[0]); i++){ ptr=distances[i]; ptr++; } I do not know how to print out the contents of the pointer to see how it works.

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• base pointer to derived class

  - by Jay

  Suppose there are Base class and Derived class. Base *A = new Base; Here A is a pointer point to Base class, and new constructs one that A points to. I also saw Base *B = new Derived; How to explain this? B is a pointer to Base Class, and a Derived class constructed and pointed by B? If there is a function derived from Base class, say, Virtual void f(), and it's been overridden in Derived class, then B->f() will invoke which version of the function? version in Base class, or version that overridden in Derived Class. What if there is a new function void g()in Derived, is B->g() going to invoke this function properly? One more is, is int *a = new double; or int *a = new int; legal?

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• puts() a pointer in C

  - by Sergey Gavruk

  I have a function: char *make_text(void) { char txt[MAXLEN]; //make something return txt; } Thats my main program: int main(void) { char *s = make_text(); puts(s); getch(); return 0; } puts(s) returns 0 and its nothing printed. Whats happened?

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• How to read some bytes from BYTE*

  - by chekalin-v

  I have BYTE pointer. For example the length of this BYTE array is 10. How can I read 4 bytes from 3 position BYTE array? Now I doing it so BYTE *source = "1234567890\0"; BYTE* tmp = new BYTE[4+1](); for(int i=0; i<4; i++) { tmp[i] = source[i+3]; }

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• Passing a pointer to a function in objective-c

  - by Chiodo

  Hi, i've a stupid questiona about passing pointer. I've this: @interface MyClass : NSObject myobj* foo; -(void)doSomething:(myobj*)aObj; @end @implementation MyClass -(void)doSomething:(myobj*)aObj { cFuncCall(&aObj); //alloc memory and init the object } -(id)init { //init stuff... [self doSomething:foo]; // foo retun 0x0!!! } @end why foo return nil??? It should be initialized by cFuncCall!

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• reopen or read and say why not reopened [closed]

  - by gcc

  input 23 3 4 4 42 n 23 0 9 9 n n n 3 9 9 x //according to input,i should create int pointer arrays. pointer arrays // starting from 1 (that is initial arrays is arrays[1].when program sees n ,it // must be jumb to arrays 2 // the first int input 23 is num_arrays which used in malloc(sizeof(int)*num_arrays expected output: elements of arrays[1] 3 4 5 42 elements of arrays[2] 23 0 9 9 elements of arrays[5] 3 9 9 another input 12 2 3 4 n n 2 3 4 n 12 3 x expected output elements of arrays[1] 2 3 4 elements of arrays[3] 2 3 4 elements of arrays[4] 12 3 specification: x is stopper n is comman to create new pointer array i am new in this site anyone help me how can i write

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• C++ run error: pointer being freed was not allocated

  - by Dale Reves

  I'm learning c++ and am working on a program that keeps giving me a 'pointer being freed was not allocated' error. It's a grocery store program that inputs data from a txt file, then user can enter item# & qty. I've read through similar questions but what's throwing me off is the 'pointer' issue. I would appreciate if someone could take a look and help me out. I'm using Netbeans IDE 7.2 on a Mac. I'll just post the whole piece I have so far. Thx. #include <iostream> #include <fstream> #include <string> #include <vector> using namespace std; class Product { public: // PLU Code int getiPluCode() { return iPluCode; } void setiPluCode( int iTempPluCode) { iPluCode = iTempPluCode; } // Description string getsDescription() { return sDescription; } void setsDescription( string sTempDescription) { sDescription = sTempDescription; } // Price double getdPrice() { return dPrice; } void setdPrice( double dTempPrice) { dPrice = dTempPrice; } // Type..weight or unit int getiType() { return iType; } void setiType( int iTempType) { iType = iTempType; } // Inventory quantity double getdInventory() { return dInventory; } void setdInventory( double dTempInventory) { dInventory = dTempInventory; } private: int iPluCode; string sDescription; double dPrice; int iType; double dInventory; }; int main () { Product paInventory[21]; // Create inventory array Product paPurchase[21]; // Create customer purchase array // Constructor to open inventory input file ifstream InputInventory ("inventory.txt", ios::in); //If ifstream could not open the file if (!InputInventory) { cerr << "File could not be opened" << endl; exit (1); }//end if int x = 0; while (!InputInventory.eof () ) { int iTempPluCode; string sTempDescription; double dTempPrice; int iTempType; double dTempInventory; InputInventory >> iTempPluCode >> sTempDescription >> dTempPrice >> iTempType >> dTempInventory; paInventory[x].setiPluCode(iTempPluCode); paInventory[x].setsDescription(sTempDescription); paInventory[x].setdPrice(dTempPrice); paInventory[x].setiType(iTempType); paInventory[x].setdInventory(dTempInventory); x++; } bool bQuit = false; //CREATE MY TOTAL VARIABLE HERE! int iUserItemCount; do { int iUserPLUCode; double dUserAmount; double dAmountAvailable; int iProductIndex = -1; //CREATE MY SUBTOTAL VARIABLE HERE! while(iProductIndex == -1) { cout<<"Please enter the PLU Code of the product."<< endl; cin>>iUserPLUCode; for(int i = 0; i < 21; i++) { if(iUserPLUCode == paInventory[i].getiPluCode()) { dAmountAvailable = paInventory[i].getdInventory(); iProductIndex = i; } } //PLU code entry validation if(iProductIndex == -1) { cout << "You have entered an invalid PLU Code."; } } cout<<"Enter the quantity to buy.\n"<< "There are "<< dAmountAvailable << "available.\n"; cin>> dUserAmount; while(dUserAmount > dAmountAvailable) { cout<<"That's too many, please try again"; cin>>dUserAmount; } paPurchase[iUserItemCount].setiPluCode(iUserPLUCode);// Array of objects function calls paPurchase[iUserItemCount].setdInventory(dUserAmount); paPurchase[iUserItemCount].setdPrice(paInventory[iProductIndex].getdPrice()); paInventory[iProductIndex].setdInventory( paInventory[iProductIndex].getdInventory() - dUserAmount ); iUserItemCount++; cout <<"Are you done purchasing items? Enter 1 for yes and 0 for no.\n"; cin >> bQuit; //NOTE: Put Amount * quantity for subtotal //NOTE: Put code to update subtotal (total += subtotal) // NOTE: Need to create the output txt file! }while(!bQuit); return 0; }

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• How do I repass a function pointer in C++

  - by fneep

  Firstly, I am very new to function pointers and their horrible syntax so play nice. I am writing a method to filter all pixels in my bitmap based on a function that I pass in. I have written the method to dereference it and call it in the pixel buffer but I also need a wrapper method in my bitmap class that takes the function pointer and passes it on. How do I do it? What is the syntax? I'm a little stumped. Here is my code with all the irrelevant bits stripped out and files combined (read all variables initialized filled etc.). struct sColour { unsigned char r, g, b, a; }; class cPixelBuffer { private: sColour* _pixels; int _width; int _height; int _buffersize; public: void FilterAll(sColour (*FilterFunc)(sColour)); }; void cPixelBuffer::FilterAll(sColour (*FilterFunc)(sColour)) { // fast fast fast hacky FAST for (int i = 0; i < _buffersize; i++) { _pixels[i] = (*FilterFunc)(_pixels[i]); } } class cBitmap { private: cPixelBuffer* _pixels; public: inline void cBitmap::Filter(sColour (*FilterFunc)(sColour)) { //HERE!! } };

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• Pointer problem in C for char*

  - by egebilmuh

  Hi guys, i use pointer for holding name and research lab property. But when i print the existing Vertex ,when i print the vertex, i cant see so -called attributes properly. For example though real value of name is "lancelot" , i see it as wrong such as "asdasdasdasd" struct vertex { int value; char*name; char* researchLab; struct vertex *next; struct edge *list; }; void GRAPHinsertV(Graph G, int value,char*name,char*researchLab) { //create new Vertex. Vertex newV = malloc(sizeof newV); // set value of new variable to which belongs the person. newV->value = value; newV->name=name; newV->researchLab=researchLab; newV->next = G->head; newV->list = NULL; G->head = newV; G->V++; } /*** The method creates new person. **/ void createNewPerson(Graph G) { int id; char name[30]; char researchLab[30]; // get requeired variables. printf("Enter id of the person to be added.\n"); scanf("%d",&id); printf("Enter name of the person to be added.\n"); scanf("%s",name); printf("Enter researc lab of the person to be added\n"); scanf("%s",researchLab); // insert the people to the social network. GRAPHinsertV(G,id,name,researchLab); } void ListAllPeople(Graph G) { Vertex tmp; Edge list; for(tmp = G->head;tmp!=NULL;tmp=tmp->next) { fprintf(stdout,"V:%d\t%s\t%s\n",tmp->value,tmp->name,tmp->researchLab); } system("pause"); }

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• Getting value from pointer

  - by Eric

  Hi, I'm having problem getting the value from a pointer. I have the following code in C++: void* Nodo::readArray(VarHash& var, string varName, int posicion, float& d) { //some code before... void* res; float num = bit.getFloatFromArray(arregloTemp); //THIS FUNCTION RETURN A FLOAT AND IT'S OK cout << "NUMBER " << num << endl; d = num; res = &num; return res } int main() { float d = 0.0; void* res = n.readArray(v, "c", 0, d); //THE VALUES OF THE ARRAY ARE: {65.5, 66.5}; float* car3 = (float*)res; cout << "RESULT_READARRAY " << *car3 << endl; cout << "FLOAT REFERENCE: " << d << endl; } The result of running this code is the following: NUMBER 65.5 RESULT_READARRAY -1.2001 //INCORRECT IT SHOULD BE LIKE NUMBER FLOAT REFERENCE: 65.5 //CORRECT NUMBER 66.5 RESULT_READARRAY -1.2001 //INCORRECT IT SHOULD BE LIKE NUMBER FLOAT REFERENCE: 66.5 //CORRECT For some reason, when I get the value of the pointer returned by the function called readArray is incorrect. I'm passing a float variable(d) as a reference in the same function just to verify that the value is ok, and as you can see, THE FLOAT REFERENCE matches the NUMBER. If I declare the variable num(read array) as a static float, the first RESULT_READARRAY will be 65.5, that is correct, however, the next value will be the same instead of 66.5. Let me show you the result of running the code using static float variable: NUMBER 65.5 RESULT_READARRAY 65.5 //PERFECT FLOAT REFERENCE: 65.5 //¨PERFECT NUMBER 65.5 //THIS IS INCORRECT, IT SHOULD BE 66.5 RESULT_READARRAY 65.5 FLOAT REFERENCE: 65.5 Do you know how can I get the correct value returned by the function called readArray()?

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• Equivalent to window.setTimeout() for C++

  - by bobobobo

  In javascript there's this sweet, sweet function window.setTimeout( func, 1000 ) ; which will asynchronously invoke func after 1000 ms. I want to do something similar in C++ (without multithreading), so I put together a sample loop like: #include <stdio.h> struct Callback { // The _time_ this function will be executed. double execTime ; // The function to execute after execTime has passed void* func ; } ; // Sample function to execute void go() { puts( "GO" ) ; } // Global program-wide sense of time double time ; int main() { // start the timer time = 0 ; // Make a sample callback Callback c1 ; c1.execTime = 10000 ; c1.func = go ; while( 1 ) { // its time to execute it if( time c1.execTime ) { c1.func ; // !! doesn't work! } time++; } } How can I make something like this work?

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• Assign C++ instance method to a global-function-pointer ?

  - by umanga

  Greetings, My project structure is as follows: \- base (C static library) callbacks.h callbacks.c paint_node.c . . * libBase.a \-app (C++ application) main.cpp In C library 'base' , I have declared global-function-pointer as: in singleheader file callbacks.h #ifndef CALLBACKS_H_ #define CALLBACKS_H_ extern void (*putPixelCallBack)(); extern void (*putImageCallBack)(); #endif /* CALLBACKS_H_ */ in single C file they are initialized as callbacks.c #include "callbacks.h" void (*putPixelCallBack)(); void (*putImageCallBack)(); Other C files access this callback-functions as: paint_node.c #include "callbacks.h" void paint_node(node *node,int index){ //Call callbackfunction . . putPixelCallBack(node->x,node->y,index); } I compile these C files and generate a static library 'libBase.a' Then in C++ application, I want to assign C++ instance method to this global function-pointer: I did something like follows : in Sacm.cpp file #include "Sacm.h" extern void (*putPixelCallBack)(); extern void (*putImageCallBack)(); void Sacm::doDetection() { putPixelCallBack=(void(*)())&paintPixel; //call somefunctions in 'libBase' C library } void Sacm::paintPixel(int x,int y,int index) { qpainter.begin(this); qpainter.drawPoint(x,y); qpainter.end(); } But when compiling it gives the error: sacmtest.cpp: In member function ‘void Sacm::doDetection()’: sacmtest.cpp:113: error: ISO C++ forbids taking the address of an unqualified or parenthesized non-static member function to form a pointer to member function. Say ‘&Sacm::paintPixel’ sacmtest.cpp:113: error: converting from ‘void (Sacm::)(int, int, int)’ to ‘void ()()’ Any tips?

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• bubble sort on array of c structures not sorting properly

  - by xmpirate

  I have the following program for books record and I want to sort the records on name of book. the code isn't showing any error but it's not sorting all the records. #include "stdio.h" #include "string.h" #define SIZE 5 struct books{ //define struct char name[100],author[100]; int year,copies; }; struct books book1[SIZE],book2[SIZE],*pointer; //define struct vars void sort(struct books *,int); //define sort func main() { int i; char c; for(i=0;i<SIZE;i++) //scanning values { gets(book1[i].name); gets(book1[i].author); scanf("%d%d",&book1[i].year,&book1[i].copies); while((c = getchar()) != '\n' && c != EOF); } pointer=book1; sort(pointer,SIZE); //sort call i=0; //printing values while(i<SIZE) { printf("##########################################################################\n"); printf("Book: %s\nAuthor: %s\nYear of Publication: %d\nNo of Copies: %d\n",book1[i].name,book1[i].author,book1[i].year,book1[i].copies); printf("##########################################################################\n"); i++; } } void sort(struct books *pointer,int n) { int i,j,sorted=0; struct books temp; for(i=0;(i<n-1)&&(sorted==0);i++) //bubble sort on the book name { sorted=1; for(j=0;j<n-i-1;j++) { if(strcmp((*pointer).name,(*(pointer+1)).name)>0) { //copy to temp val strcpy(temp.name,(*pointer).name); strcpy(temp.author,(*pointer).author); temp.year=(*pointer).year; temp.copies=(*pointer).copies; //copy next val strcpy((*pointer).name,(*(pointer+1)).name); strcpy((*pointer).author,(*(pointer+1)).author); (*pointer).year=(*(pointer+1)).year; (*pointer).copies=(*(pointer+1)).copies; //copy back temp val strcpy((*(pointer+1)).name,temp.name); strcpy((*(pointer+1)).author,temp.author); (*(pointer+1)).year=temp.year; (*(pointer+1)).copies=temp.copies; sorted=0; } *pointer++; } } } My Imput The C Programming Language X Y Z 1934 56 Inferno Dan Brown 1993 453 harry Potter and the soccers stone J K Rowling 2012 150 Ruby On Rails jim aurther nil 2004 130 Learn Python Easy Way gmaps4rails 1967 100 And the output ########################################################################## Book: Inferno Author: Dan Brown Year of Publication: 1993 No of Copies: 453 ########################################################################## ########################################################################## Book: The C Programming Language Author: X Y Z Year of Publication: 1934 No of Copies: 56 ########################################################################## ########################################################################## Book: Ruby On Rails Author: jim aurther nil Year of Publication: 2004 No of Copies: 130 ########################################################################## ########################################################################## Book: Learn Python Easy Way Author: gmaps4rails Year of Publication: 1967 No of Copies: 100 ########################################################################## ########################################################################## Book: Author: Year of Publication: 0 No of Copies: 0 ########################################################################## We can see the above sorting is wrong? What I'm I doing wrong?

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• Callback function and function pointer trouble in C++ for a BST

  - by Brendon C.

  I have to create a binary search tree which is templated and can deal with any data types, including abstract data types like objects. Since it is unknown what types of data an object might have and which data is going to be compared, the client side must create a comparison function and also a print function (because also not sure which data has to be printed). I have edited some C code which I was directed to and tried to template, but I cannot figure out how to configure the client display function. I suspect variable 'tree_node' of class BinarySearchTree has to be passed in, but I am not sure how to do this. For this program I'm creating an integer binary search tree and reading data from a file. Any help on the code or the problem would be greatly appreciated :) Main.cpp #include "BinarySearchTreeTemplated.h" #include <iostream> #include <fstream> #include <string> using namespace std; /*Comparison function*/ int cmp_fn(void *data1, void *data2) { if (*((int*)data1) > *((int*)data2)) return 1; else if (*((int*)data1) < *((int*)data2)) return -1; else return 0; } static void displayNode() //<--------NEED HELP HERE { if (node) cout << " " << *((int)node->data) } int main() { ifstream infile("rinput.txt"); BinarySearchTree<int> tree; while (true) { int tmp1; infile >> tmp1; if (infile.eof()) break; tree.insertRoot(tmp1); } return 0; } BinarySearchTree.h (a bit too big to format here) http://pastebin.com/4kSVrPhm

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• Accessing derived class members with a base class pointer

  - by LRB

  I am making a simple console game in C++ I would like to know if I can access members from the 'entPlayer' class while using a pointer that is pointing to the base class ( 'Entity' ): class Entity { public: void setId(int id) { Id = id; } int getId() { return Id; } protected: int Id; }; class entPlayer : public Entity { string Name; public: entPlayer() { Name = ""; Id = 0; } void setName(string name) { Name = name; } string getName() { return Name; } }; Entity *createEntity(string Type) { Entity *Ent = NULL; if (Type == "player") { Ent = new entPlayer; } return Ent; } void main() { Entity *ply = createEntity("player"); ply->setName("Test"); ply->setId(1); cout << ply->getName() << endl; cout << ply->getId() << endl; delete ply; } How would I be able to call ply-setName etc? OR If it's not possible that way, what would be a better way?

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• Recommendations for screen-capture tool that retains menus and mouse pointer

  - by Chris Farmer

  There are several screen capture tool questions already on this site, but I think I have a slight tweak to the usual. I'd like a handy screen capture utility that can: Run in Windows 7 Capture a sub-region of the screen Show the current state of the mouse cursor and any active menus I'd like to use it for writing docs that refer to specific application menu items. I like the built-in snipping tool in Windows 7, but the act of using it dismisses my menus, and it doesn't get the mouse cursor either. Do any such tools exist? EDIT: Ahh, I wasn't familiar with the "delayed capture" options of these tools, but they all seem to fit the bill. Thanks!

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• Selective Pointer device remapping in linux

  - by user6368

  I just got an HP 2710p (hp tablet, with digitizer), and I've played around with linux for a while now, and thought I would go ahead and install it. Everything works fine, excepting normal tablet functions, which is to be expected. I'm working on the screen rotation, and there are on-screen keyboards, etc, but I'm having issues with the stylus. I can tap and left click with the stylus as normal, but the side button (which in windows functions as a right mouse button) appears as a 'button 2' to xev (a middle/scroll wheel button). I can switch 'button 2' and 'button 3' universally using xmodmap, but I'd like to do so exclusively for stylus so I don't screw up regular pointing devices. Altering xorg.conf (which is surprisingly bare) with the recommended sections (adding sections for each of the stylus buttons) does nothing. I'm running crunchbang, which is an ubuntu/debian varient with openbox as the windows manager. Thanks Also, as a seperate note, does anybody know how to detect when I rotate and/or latch the lid shut? I was thinking maybe I could run a script to switch the buttons when I close it, but I can't find any information.

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• Toshiba laptop only shows black screen with mouse pointer after starting up

  - by BubblySue

  I only see black screen after the startup. It just shows the logo and the status bar upon start, then it goes black screen with moveable cursor. I tried alt+ctrl+del, but it doesn't work. I pressed shift 5 times and it makes a sound. I already removed battery and restarted it, but still the same. I can go to safe mode and scanned thru there. Still, desktop won't show up. Don't know what else to check?

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• Toshiba laptop only shows black screen with mouse pointer after starting up

  - by BubblySue

  I only see black screen after the startup. It just shows the logo and the status bar upon start, then it goes black screen with moveable cursor. I tried alt+ctrl+del, but it doesn't work. I pressed shift 5 times and it makes a sound. I already removed battery and restarted it, but still the same. I can go to safe mode and scanned thru there. Still, desktop won't show up. Don't know what else to check?

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• DNS Pointer to old server name

  - by TechKnow Dude

  We have a SBS2003 server that was migrated to a new hardware platform, the computer name has changed but the domain is the same. The desktop's are trying to do offline files to the old server name. There is a nslookup entry for the old server name and a DNS entry for the old server. How do we safely remove the old DNS entry without breaking the computer offline folder storage locally. Can we change the pointing location on the offline file storage to point to the new server name.

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• Image annotation with Inkscape, Pointer and explanation for objects in picture

  - by None

  I need straight paths with end markers for associating text to parts of the image. For better readability, it needs to be high-contrast, i.e. a white line with black outline. Stroke to path will create a group of a box and a circle from the line with end marker. This makes placement of the markers more difficult, as with the node tool it is just a matter of dragging the end nodes of a line segment. I will try to place the markers as line for now and only finally converting them to an outline.

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• Converting a pointer for a base class into an inherited class

  - by Shawn B

  Hey, I'm working on a small roguelike game, and for any object/"thing" that is not a part of the map is based off an XEntity class. There are several classes that depend on it, such as XPlayer, XItem, and XMonster. My problem is, that I want to convert a pointer from XEntity to XItem when I know that an object is in item. The sample code I am using to pick up an item is this, it is when a different entity picks up an item it is standing over. void XEntity::PickupItem() { XEntity *Ent = MapList; // Start of a linked list while(true) { if(Ent == NULL) { break; } if(Ent->Flags & ENT_ITEM) { Ent->RemoveEntity(); // Unlink from the map's linked list XItem *Item = Ent // Problem is here, type-safety // Code to link into inventory is here break; } Ent = Ent->MapList; } } My first thought was to create a method in XEntity that returns itself as an XItem pointer, but it creates circular dependencies that are unresolvable. I'm pretty stumped about this one. Any help is greatly appreciated.

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