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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • Arry 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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  • 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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  • Does this have anything to do with endian-ness?

    - by eSKay
    This piece of code: #include<stdio.h> void hello() { printf("hello\n"); } void bye() { printf("bye\n"); } int main() { printf("%p\n", hello); printf("%p\n", bye); return 0; } output on my machine: 0x80483f4 0x8048408 [second address is bigger in value] on Codepad 0x8048541 0x8048511 [second address is smaller in value] Does this have anything to do with endian-ness of the machines? If not, Why the difference in the ordering of the addresses? Also, Why the difference in the difference? 0x8048541 - 0x8048511 = 0x30 0x8048408 - 0x80483f4 = 0x14 Btw, I just checked. This code (taken from here) says that both the machines are Little-Endian #include<stdio.h> int main() { int num = 1; if(*(char *)&num == 1) printf("Little-Endian\n"); else printf("Big-Endian\n"); return 0; }

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