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• Pointers to threads

  - by viswanathan

  Suppose i have pointer to a thread like this CWinThread *m_pThread = AfxBeginThread(StartThread, this, THREAD_PRIORITY_NORMAL, 0, 0); Now in my StartThread function assume i did all operations and the function returned like this UINT CClassThread::StartThread(LPVOID pVoid) { return true; } Will my m_pThread be invalid when the return statement is executed?

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• Pointers to structs

  - by Bobby

  I have the following struct: struct Datastore_T { Partition_Datastores_T cmtDatastores; // bytes 0 to 499 Partition_Datastores_T cdhDatastores; // bytes 500 to 999 Partition_Datastores_T gncDatastores; // bytes 1000 to 1499 Partition_Datastores_T inpDatastores; // bytes 1500 1999 Partition_Datastores_T outDatastores; // bytes 2000 to 2499 Partition_Datastores_T tmlDatastores; // bytes 2500 to 2999 Partition_Datastores_T sm_Datastores; // bytes 3000 to 3499 }; I want to set a char* to struct of this type like so: struct Datastore_T datastores; // Elided: datastores is initialized with data here char* DatastoreStartAddr = (char*)&datastores; memset(DatastoreStartAddr, 0, sizeof(Datastore_T)); The problem I have is that the value that DatastoreStartAddr points to always has a value of zero when it should point to the struct that has been initialized with data. Meaning if I change the values in the struct using the struct directly, the values pointed to by DatastoreStartAddr should also change b/c they are pointing to the same address. But this is not happening. What am I doing wrong?

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• va_arg with pointers

  - by Yktula

  I want to initialize a linked list with pointer arguments like so: /* * Initialize a linked list using variadic arguments * Returns the number of structures initialized */ int init_structures(struct structure *first, ...) { struct structure *s; unsigned int count = 0; va_list va; va_start(va, first); for (s = first; s != NULL; s = va_arg(va, (struct structure *))) { if ((s = malloc(sizeof(struct structure))) == NULL) { perror("malloc"); exit(EXIT_FAILURE); } count++; } va_end(va); return count; } The problem is that clang errors type name requires a specifier or qualifier at va_arg(va, (struct structure *)), and says that the type specifier defaults to int. It also notes instantiated form at (struct structure *) and struct structure *. This, what seems to be getting assigned to s is int (struct structure *). It compiles fine when parentheses are removed from (struct structure *), but the structures that are supposed to be initialized are inaccessible. Why is int assumed when parentheses are around the type argument passed to va_arg? How can I fix this?

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• C question about pointers and arrays

  - by Dj

  char a[]="HELLO"; char *p="HELLO"; will a[2] and p[2] fetch the same character?

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• Viewing array of pointers to structures in Visual Studio in the debugger

  - by Fozi

  I'm having a problem displaying the contents of a pointer array with its contents in the debugger. If I just add the pointer to the watch only the fist entry is visible. But if I add the length to it the debugger assumes that I have something like array[length][length]. Picture The first entry is the broken one, looks the same with ,2 or with any ,2 x. The second one is what I would like to see, but for more entries. Edit: The two entries displayed as [x][1] are invalid. I'm using VS 2005 but I think I had this problem on 2008 as well. Is this a bug or am I doing something wrong?

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• If statement question iphone?

  - by NextRev

  I am creating a game where where you complete shapes and the area gets filled in. However, if there is an enemy bird within your shape, it will not fill in. I want to make it so that if you do trap a bird within your shape, you will lose a life. How can I write an if statement that pretty much says if the below code doesn't take place, then you lose a life. If it helps losing a life is called doDie in my code. -(void)fillMutablePath{ CGPoint movePoint = CGPointFromString([pointsToFillArray objectAtIndex:0]); CGPathMoveToPoint(fillPath, NULL, movePoint.x, movePoint.y); for (int i=0; i<[pointsToFillArray count]; i++) { CGPoint tempPoint = CGPointFromString([pointsToFillArray objectAtIndex:i]); CGPathAddLineToPoint(fillPath, NULL, tempPoint.x, tempPoint.y); } CGContextAddPath(gameViewObj._myContext, fillPath); CGContextFillPath(gameViewObj._myContext); CGPathRelease(fillPath); [pointsToFillArray removeAllObjects]; } if(fillMutablePath doesn't take place when making a shape){ [self doDie]; } Like i said above, the reason fillMutablePath wouldn't take place is because a bird would be trapped within the shape. Any help would be much appreciated!!

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• Pointers, links, object and reference count

  - by EugeneP

  String a = "a"; // allocate memory and write address of a memory block to a variable String b = "b"; // in a and b hold addresses b = a; // copy a address into b. // Now what? b value is completely lost and will be garbage collected //* next step a = null; // now a does not hold a valid address to any data, // still data of a object exist somewhere, yet we cannot get access to it. Correct me if there's a mistake somewhere in my reflexions. My question is: suppose anInstance object of type Instance has a property ' surname ' anInstance.getSurname() returns "MySurname". now String s = anInstance.getSurname(); anInstance = null; question is - is it true that getSurname value, namely MySurname will not be garbage collected because and only because it has active reference counter 0, and if other properties of anInstance have a zero reference counter, they'll be garbage collected?

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• Array of pointers in Objective-C using NSArray

  - by Amir

  Hello, I am writting program for my iphone and have a qestion. lets say i have class named my_obj class my_obj { NSString *name; NSinteger *id; NSinteger *foo; NSString *boo; } now i allocate 100 objects from type my_obj and insert them to array from type NSArray. then i want to sort the Array in two different ways. one by the name and the second by the id. i want to allocate another two arrays from type NSArray *arraySortByName *arraySortById what i need to do if i just want the sorted arrays to be referenced to the original array so i will get two sorted arrays that point to the original array (that didnt changed!) i other word i dont want to allocate another 100 objects to each sorted array.

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• A question on vectors, pointers and iterators

  - by xbonez

  Guys, I have a midterm examination tomorrow, and I was looking over the sample paper, and I'm not sure about this question. Any help would be appreciated. Let v be a vector<Thingie*>, so that each element v[i] contains a pointer to a Thingie. If p is a vector<Thingie*>::iterator, answer the following questions: what type is p? what type is *p? what code provides the address of the actual Thingie? what code provides the actual Thingie?

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• Unable to free const pointers in C

  - by lego69

  How can I free a const char*? I allocated new memory using malloc, and when I'm trying to free it I always receive the error "incompatible pointer type" The code that causes this is something like: char* name="Arnold"; const char* str=(const char*)malloc(strlen(name)+1); free(str); // error here

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• Double indirection and structures passed into a function

  - by ZPS

  I am curious why this code works: typedef struct test_struct { int id; } test_struct; void test_func(test_struct ** my_struct) { test_struct my_test_struct; my_test_struct.id=267; *my_struct = &my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); } This works, but pointing to the memory address of a functions local variable is a big no-no, right? But if i used a structure pointer and malloc, that would be the correct way, right? void test_func(test_struct ** my_struct) { test_struct *my_test_struct; my_test_struct = malloc(sizeof(test_struct)); my_test_struct->id=267; *my_struct = my_test_struct; } int main () { test_struct * main_struct; test_func(&main_struct); printf("%d\n",main_struct->id); }

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• How to store a function in a member of class? (Using function as callback)

  - by Dane

  I want to store a function as a class member and call it inside the class? Pretty much like a callback function. My class draw a document but every document must drawn differently. So I want to assign a function (written outside of the class) into one of the members of the class and then call it when I want to draw the document. This function mostly is responsible for transforming objects according to each specific document. Here is my class: class CDocument { public: CDocument(); ~CDocument(); void *TransFunc(); } void Transform() { } int main() CDocument* Doc = new CDocument(); Doc->TransFunc = Transform(); } I know that this is probably simple question, but I couldn't find the answer by googling or searching SO.

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• Passing array to function with pointer loses array size information!

  - by Narek

  If I write int main() { int a[100] = {1,2,3,4,}; cout<<sizeof(a)/sizeof(a[0])<<endl; return 0; } I get 400! If I write void func(int *a); int main() { int a[100] = {1,2,3,4,}; func(a); return 0; } void func(int *a) { cout<<sizeof(a)/sizeof(a[0])<<endl; } Then I get 400! So why passing array to function with pointer loses array size information?

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• Pointers for monitoring drupal 6 site needed, difference in server aw stats and the core "statistics

  - by Saurabh

  The IP addresses logged in by the Drupal 6 core "Statistics" module are not being displayed by the AW statistics displayed by my hosting server (hostgator). I am not able to comprehend why and which statistics are more reliable ? Also I would request some light to be shed on the best practices to monitor a Drupal 6 website. Thanks for your help people.

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• Seg Fault with malloc'd pointers

  - by anon

  I'm making a thread class to use as a wrapper for pthreads. I have a Queue class to use as a queue, but I'm having trouble with it. It seems to allocate and fill the queue struct fine, but when I try to get the data from it, it Seg. faults. http://pastebin.com/Bquqzxt0 (the printf's are for debugging, both throw seg faults) edit: the queue is stored in a dynamically allocated "struct queueset" array as a pointer to the data and an index for the data

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• Segmentation fault on returning from main (very short and simple code, no arrays or pointers)

  - by Gábor Kovács

  I've been wondering why the following trivial code produces a segmentation fault when returning from main(): //Produces "Error while dumping state (probably corrupted stack); Segmentation fault" #include <iostream> #include <fstream> #include <vector> using namespace std; class Test { vector<int> numbers; }; int main() { Test a; ifstream infile; cout << "Last statement..." << endl; // this gets executed return 0; } Interestingly, 1) if only one of the two variables is declared, I don't get the error, 2) if I declare a vector variable instead of an object with a vector member, everything's fine, 3) if I declare an ofstream instead of an ifstream, again, everything works fine. Something appears to be wrong with this specific combination... Could this be a compiler bug? I use gcc version 3.4.4 with cygwin. Thanks for the tips in advance. Gábor

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• Setting pointers to structs

  - by Bobby

  I have the following struct: struct Datastore_T { Partition_Datastores_T cmtDatastores; // bytes 0 to 499 Partition_Datastores_T cdhDatastores; // bytes 500 to 999 Partition_Datastores_T gncDatastores; // bytes 1000 to 1499 Partition_Datastores_T inpDatastores; // bytes 1500 1999 Partition_Datastores_T outDatastores; // bytes 2000 to 2499 Partition_Datastores_T tmlDatastores; // bytes 2500 to 2999 Partition_Datastores_T sm_Datastores; // bytes 3000 to 3499 }; I want to set a char* to struct of this type like so: struct Datastore_T datastores; // Elided: datastores is initialized with data here char* DatastoreStartAddr = (char*)&datastores; memset(DatastoreStartAddr, 0, 3500); The problem I have is that DatastoreStartAddr always has a value of zero when it should point to the struct that has been initialized with data. What am I doing wrong?

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• Do not properly deleted pointers fragment memory?

  - by SoulBeaver

  That's basically the question. If I have a pointer int *a = &someIntVar and I do not delete it over the course of the program, does it stay in memory after the program has terminated? Is this a case of data fragmentation?

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• C++ Pointers to functions.

  - by Andy Leman

  using namespace std; int addition (int a, int b) { return (a+b); } int subtraction (int a, int b) { return (a-b); } int operation (int x, int y, int (*functocall)(int,int)) { int g; g = (*functocall)(x,y); return(g); } int main() { int m,n; int (*minus)(int,int) = subtraction; m = operation (7,5,addition); n = operation (20,m,minus); cout << n; return 0; } Can anybody explain this line for me int (*minus)(int,int) = subtraction; Thanks a lot!

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• How to "pin" C++/CLI pointers

  - by Kumar

  I am wrapping up a class which reading a custom binary data file and makes the data available to a .net/c# class However a couple of lines down the code, i start getting the memory access violation error which i believe is due to the GC moving memory around, the class is managed Here's the code if ( ! reader.OpenFile(...) ) return ; foreach(string fieldName in fields) { int colIndex = reader.GetColIndex( fieldName ); int colType = reader.GetColType( colIndex ); // error is raised here on 2nd iteration } for ( int r = 0 ; r < reader.NumFields(); r++ ) { foreach(string fieldName in fields) { int colIndex = reader.GetColIndex( fieldName ); int colType = reader.GetColType( colIndex ); // error is raised here on 2nd iteration switch ( colType ) { case 0 : // INT processField( r, fieldName, reader.GetInt(r,colIndex) ); break ; .... } } } .... i've looked at interior_ptr, pin_ptr but they give an error c3160 cannot be in a managed class Any workaround ? BTW, this is my 1st C++ program in a very long time !

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• Pointer to another classs as a property

  - by arjacsoh

  Why I receive an error when I try to create a property to another class through a pointer like that: #ifndef SQUARE_H #define SQUARE_H #include <string> //using namespace std; #include "Player.h" class Square { public: Square(int); void process(); protected: int ID; Player* PlayerOn; <--- }; #endif and the Player class is : #ifndef PLAYER_H #define PLAYER_H #include <string> //using namespace std; #include "Square.h" class Player { public: Player(int,int); // ~Player(void); int playDice(); private: int ID; int money; }; #endif I receive: syntax error missing ; before * (on the declaration of Player* PlayerOn;) and missing type specifier (on the same line...)

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• subscript operator on pointers

  - by Lodle

  If i have a pointer to an object that has an overloaded subscript operator ( [] ) why cant i do this: MyClass *a = new MyClass(); a[1]; but have to do this instead: MyClass *a = new MyClass(); (*a)[1];

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• C++ class with char pointers returning garbage

  - by JMP

  I created a class "Entry" to handle Dictionary entries, but in my main(), I create the Entry() and try to cout the char typed public members, but I get garbage. When I look at the Watch list in debugger, I see the values being set, but as soon as I access the values, there is garbage. Can anyone elaborate on what I might be missing? #include <iostream> using namespace std; class Entry { public: Entry(const char *line); char *Word; char *Definition; }; Entry::Entry(const char *line) { char tmp[100]; strcpy(tmp, line); Word = strtok(tmp, ",") + '\0'; Definition = strtok(0,",") + '\0'; } int main() { Entry *e = new Entry("drink,What you need after a long day's work"); cout << "Word: " << e->Word << endl; cout << "Def: " << e->Definition << endl; cout << endl; delete e; e = 0; return 0; }

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• Function pointers in javascript using django

  - by Hulk

  Is this a valid function pointer code below, In views , def change(request): dict={} function_ptr="create()" dict.update({'function_ptr' : function_ptr}) return render_to_response('mpjt/create.html',context_instance=RequestContext(request,{'dict': dict})) In create.html $(document).ready(function() { var a = '{{dict.function_ptr}}' func_ptr(a); function create() { alert('got respponse'); } }); Thanks..

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• calling resize on std vector of pointers crashed

  - by user11869

  The problem can be reproduced using VS 2013 Express. It crashed when internal vector implementation tried to deallocate the original vector. However, the problem can solved by using 'new' instead of 'malloc'. Anyone can shed some light on this? struct UndirectedGraphNode { int label; vector<UndirectedGraphNode *> neighbors; UndirectedGraphNode(int x) : label(x) {}; }; int main(int argc, char** argv) { UndirectedGraphNode* node1 = (UndirectedGraphNode*)malloc(sizeof(UndirectedGraphNode)); node1->label = 0; node1->neighbors.resize(2); return 0; }

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