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  • std::string constructor corrupts pointer

    - by computergeek6
    I have an Entity class, which contains 3 pointers: m_rigidBody, m_entity, and m_parent. Somewhere in Entity::setModel(std::string model), it's crashing. Apparently, this is caused by bad data in m_entity. The weird thing is that I nulled it in the constructor and haven't touched it since then. I debugged it and put a watchpoint on it, and it comes up that the m_entity member is being changed in the constructor for std::string that's being called while converting a const char* into an std::string for the setModel call. I'm running on a Mac, if that helps (I think I remember some problem with std::string on the Mac). Any ideas about what's going on?

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  • Forcing a templated object to construct from a pointer

    - by SalamiArmi
    I have a fictional class: template<typename T> class demonstration { public: demonstration(){} ... T *m_data; } At some point in the program's execution, I want to set m_data to a big block of allocated memory and construct an object T there. At the moment, I've been using this code: void construct() { *m_data = T(); } Which I've now realised is probably not the best idea... wont work under certain cirumstances, if T has a private assignment operator for example. Is there a normal/better way to do what I'm attempting here?

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  • pointer to a structure in a nested structure

    - by dpka6
    I have a 6 levels of nested structures. I am having problem with last three levels. The program compiles fine but when I run it crashes with Segmentation fault. There is some problem in assignment is what I feel. Kindly point out the error. typedef struct { char addr[6]; int32_t rs; uint16_t ch; uint8_t ap; } C; typedef struct { C *ap_info; } B; typedef struct { union { B wi; } u; } A; function1(char addr , int32_t rs, uint16_t ch, uint8_t ap){ A la; la.u.wi.ap_info->addr[6] = addr; la.u.wi.ap_info->rs = rs; la.u.wi.ap_info->ch = ch; la.u.wi.ap_info->ap = ap; }

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  • Auto pointer for unsigned char array?

    - by Gianluca
    I'd need a class like std::auto_ptr for an array of unsigned char*, allocated with new[]. But auto_ptr only calls delete and not delete[], so i can't use it. I also need to have a function which creates and returns the array. I came out with my own implementation within a class ArrayDeleter, which i use like in this example: #include <Utils/ArrayDeleter.hxx> typedef Utils::ArrayDeleter<unsigned char> Bytes; void f() { // Create array with new unsigned char* xBytes = new unsigned char[10]; // pass array to constructor of ArrayDeleter and // wrap it into auto_ptr return std::auto_ptr<Bytes>(new Bytes(xBytes)); } ... // usage of return value { auto_ptr<Bytes> xBytes(f()); }// unsigned char* is destroyed with delete[] in destructor of ArrayDeleter Is there a more elegant way to solve this? (Even using another "popular" library)

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  • Cryptic C++ "thing" (function pointer)

    - by m00st
    What is this syntax for in C++? Can someone point me to the technical term so I can see if I find anything in my text? At first I thought it was a prototype but then the = and (*fn) threw me off... Here is my example: void (*fn) (int&,int&) = x;

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  • EXC_BAD_ACCESS when simply casting a pointer in Obj-C

    - by AlexChilcott
    Hi all, Frequent visitor but first post here on StackOverflow, I'm hoping that you guys might be able to help me out with this. I'm fairly new to Obj-C and XCode, and I'm faced with this really... weird... problem. Googling hasn't turned up anything whatsoever. Basically, I get an EXC_BAD_ACCESS signal on a line that doesn't do any dereferencing or anything like that that I can see. Wondering if you guys have any idea where to look for this. I've found a work around, but no idea why this works... The line the broken version barfs out on is the line: LevelEntity *le = entity; where I get my bad access signal. Here goes: THIS VERSION WORKS NSArray *contacts = [self.body getContacts]; for (PhysicsContact *contact in contacts) { PhysicsBody *otherBody; if (contact.bodyA == self.body) { otherBody = contact.bodyB; } if (contact.bodyB == self.body) { otherBody = contact.bodyA; } id entity = [otherBody userData]; if (entity != nil) { LevelEntity *le = entity; CGPoint point = [contact contactPointOnBody:otherBody]; } } THIS VERSION DOESNT WORK NSArray *contacts = [self.body getContacts]; for (NSUInteger i = 0; i < [contacts count]; i++) { PhysicsContact *contact = [contacts objectAtIndex:i]; PhysicsBody *otherBody; if (contact.bodyA == self.body) { otherBody = contact.bodyB; } if (contact.bodyB == self.body) { otherBody = contact.bodyA; } id entity = [otherBody userData]; if (entity != nil) { LevelEntity *le = entity; CGPoint point = [contact contactPointOnBody:otherBody]; } } Here, the only difference between the two examples is the way I enumerate through my array. In the first version (which works) I use for (... in ...), where as in the second I use for (...; ...; ...). As far as I can see, these should be the same. This is seriously weirding me out. Anyone have any similar experience or idea whats going on here? Would be really great :) Cheers, Alex

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  • Null Pointer Exception in my BroadcastReceiver class

    - by user1760007
    I want to search a db and toast a specific column on the startup of the phone. The app keeps crashing and getting an exception even though I feel as the code is correct. @Override public void onReceive(Context ctx, Intent intent) { Log.d("omg", "1"); DBAdapter do = new DBAdapter(ctx); Log.d("omg", "2"); Cursor cursor = do.fetchAllItems(); Log.d("omg", "3"); if (cursor.moveToFirst()) { Log.d("omg", "4"); do { Log.d("omg", "5"); String title = cursor.getString(cursor.getColumnIndex("item")); Log.d("omg", "6"); // i = cursor.getInt(cursor.getColumnIndex("id")); Toast.makeText(ctx, title, Toast.LENGTH_LONG).show(); } while (cursor.moveToNext()); } cursor.close(); } The frustrating part is that I don't see any of my "omg" logs show up in logcat. I only see when my application crashes. I get three lines of errors in logcat. 10-19 12:31:11.656: E/AndroidRuntime(1471): java.lang.RuntimeException: Unable to start receiver com.test.toaster.MyReciever: java.lang.NullPointerException 10-19 12:31:11.656: E/AndroidRuntime(1471): at com.test.toaster.DBAdapter.fetchAllItems(DBAdapter.java:96) 10-19 12:31:11.656: E/AndroidRuntime(1471): at com.test.toaster.MyReciever.onReceive(MyReciever.java:26) For anyone interested, here is my DBAdapter fetchAllItems code: public Cursor fetchAllItems() { return mDb.query(DATABASE_TABLE, new String[] { KEY_ITEM, KEY_PRIORITY, KEY_ROWID }, null, null, null, null, null); }

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  • C++ function-pointer and inheritance

    - by pingvinus
    In parent class I have function, that operates under an array of functions, declared in child-class, number of functions for every child-class may vary. But since every function uses some object-variables, I can't declare them as static. I've try to do something like this: class A { public: typedef int (A::*func)(); func * fs; void f() { /*call functions from this->fs*/ } }; class B : public A { public: int smth; B(int smth) { this->smth = smth; this->fs = new func[1]; fs[0] = &B::f; } int f() { return smth + 1; } }; But, obviously it doesn't work. Any suggestions?

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  • C++ print value of a pointer

    - by user69514
    I have an array of double pointers, but every time I try do print one of the values the address gets printed. How do I print the actual value? cout << arr[i] ? cout << &arr[i] ? they both print the address Does anyone know?

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  • How to find an element in an array in C

    - by gkaykck
    I am trying to find the location of an element in the array. I have tried to use this code i generated for(i=0;i<10;i++) { if (strcmp(temp[0],varptr[i])==0) j=i; } varptr is a pointer which points to array var[11][10] and it is by the definition *varptr[11][10]. I have assigned strings to var[i] and i want to get the "i" number of my element NOT THE ADRESS. Thanks for any comment. EDit: temp is also a pointer which points to the string that i want to check. Also i am using the 2D array for keeping variable names and their address. So yes i want to keep it inside a 2D array. The question is this code is not working at all, it does not assigns i to j, so i wonder where is the problem with this idea? writing a "break" does not change if the code works or not, it just optimizes the code a little. Full Code: #include <stdio.h> #include <string.h> #include <ctype.h> double atof(char*); int main(void) { char in[100], *temp[10],var[11][10],*varptr[11][10]; int i,j, n = 0,fullval=0; double val[11]; strcpy(var[11], "ans"); for(i=0;i<11;i++) { for(j=0;j<10;j++) varptr[i][j]=&var[i][j]; } START: printf("Enter the expression: "); fflush(stdout); for(i=0;i<10;i++) temp[i]=NULL; if (fgets(in, sizeof in, stdin) != NULL) { temp[0] = strtok(in, " "); if (temp[0] != NULL) { for (n = 1; n < 10 && (temp[n] = strtok(NULL," ")) != NULL; n++) ; } if (*temp[0]=="quit") { goto FINISH;} if (isdigit(*temp[0])) { if (*temp[1]=='+') val[0] = atof(temp[0])+atof(temp[2]); else if (*temp[1]=='-') val[0] = atof(temp[0])-atof(temp[2]); else if (*temp[1]=='*') val[0] = atof(temp[0])*atof(temp[2]); else if (*temp[1]=='/') val[0] = atof(temp[0])/atof(temp[2]); printf("%s = %f\n",var[11],val[0]); goto START; } else if (temp[1]==NULL) //asking the value of a variable { for(i=0;i<10;i++) { if (strcmp(temp[0],varptr[i])==0) j=i; } printf("%s = %d\n",var[j],val[j]); goto START; } if (*temp[1]==61) { strcpy(var[fullval], temp[0]); if ((temp[3])!=NULL) { } val[fullval]=atof(temp[2]); printf("%s = %f\n",var[fullval],val[fullval]); fullval++; goto START; } if (*temp[1]!=61) { } } getch(); FINISH: return 0; }

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  • (gcc) Multi-Dim Array or Double Pointer for Warning-free Compile

    - by paul simmons
    Hi, I have a function, which is called sometimes with regular, sometimes dynamic arrays. If I define the function as function_name(int[10][10] a) and send int** as a parameter, I get a warning. Opposite, if I declare function_name(int** a) and send int[][] as a parameter (after casting) I cannot access to array elements inside function. What is the correctest way?

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  • Initializing a char array through passed pointer segfaults

    - by Bitgarden
    Ie., why does the following work: char* char_array(size_t size){ return new char[size]; } int main(){ const char* foo = "foo"; size_t len = strlen(foo); char* bar=char_array(len); memset(bar, 0, len+1); } But the following segfaults: void char_array(char* out, size_t size){ out= new char[size]; } int main(){ const char* foo = "foo"; size_t len = strlen(foo); char* bar; char_array(bar, len); memset(bar, 0, len+1); }

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  • Writing to pointer out of bounds after malloc() not causing error

    - by marr
    Hi, when I try the code below it works fine. Am I missing something? main() { int *p; p=malloc(sizeof(int)); printf("size of p=%d\n",sizeof(p)); p[500]=999999; printf("p[0]=%d",p[500]); return 0; } I tried it with malloc(0*sizeof(int)) or anything but it works just fine. The program only crashes when I don't use malloc at all. So even if I allocate 0 memory for the array p, it still stores values properly. So why am I even bothering with malloc then?

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  • "assignment makes integer from pointer without a cast " warning in c

    - by mekasperasky
    #include<stdio.h> /* this is a lexer which recognizes constants , variables ,symbols, identifiers , functions , comments and also header files . It stores the lexemes in 3 different files . One file contains all the headers and the comments . Another file will contain all the variables , another will contain all the symbols. */ int main() { int i=0,j; char a,b[20],c[30]; FILE *fp1,*fp2; c[0]='"if"; c[1]="then"; c[2]="else"; c[3]="switch"; c[4]="printf"; c[5]="scanf"; c[6]="NULL"; c[7]="int"; c[8]="char"; c[9]="float"; c[10]="long"; c[11]="double"; c[12]="char"; c[13]="const"; c[14]="continue"; c[15]="break"; c[16]="for"; c[17]="size of"; c[18]="register"; c[19]="short"; c[20]="auto"; c[21]="while"; c[22]="do"; c[23]="case"; fp1=fopen("source.txt","r"); //the source file is opened in read only mode which will passed through the lexer fp2=fopen("lext.txt","w"); //now lets remove all the white spaces and store the rest of the words in a file if(fp1==NULL) { perror("failed to open source.txt"); //return EXIT_FAILURE; } i=0; while(!feof(fp1)) { a=fgetc(fp1); if(a!=' ') { b[i]=a; } else { for (j=0;j<23;j++) { if(c[j]==b) { fprintf(fp2, "%.20s\n", c[j]); continue ; } b[i]='\0'; fprintf(fp2, "%.20s\n", b); i=0; continue; } //else if //{ i=i+1; /*Switch(a) { case EOF :return eof; case '+':sym=sym+1; case '-':sym=sym+1; case '*':sym=sym+1; case '/':sym=sym+1; case '%':sym=sym+1; case ' */ } fclose(fp1); fclose(fp2); return 0; } This is my c code for lexical analysis .. its giving warnings and also not writing anything into the lext file ..

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  • Typcast a null pointer to char*

    - by user326253
    Suppose I have a char* elem that is supposed to hold a char*, s.t. elem[0] = char*, elem[1...m]= more chars. Is there a way I can put a null ptr within char* elem? When I try to set elem = NULL, it gives me a type error because NULL is an int. Any help would be greatly appreciated!

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  • Lots of pointer casts in QGraphicsView framework and performance

    - by kleimola
    Since most of the convenience functions of QGraphicsScene and QGraphicsItem (such as items(), collidingItems(), childItems() etc.) return a QList you're forced to do lots of qgraphicsitem_cast or static_cast and QGraphicsItem::Type() checks to get hold of the actual items when you have lots of different type of items in the scene. I thought doing lots of subclass casts were not a desirable coding style, but I guess in this case there are no other viable way, or is there? QList<QGraphicsItem *> itemsHit = someItem->collidingItems(Qt::IntersectsItemShape); foreach (QGraphicsItem *item, itemsHit) { if (item->type() == QGraphicsEllipseItem::type()) { QGraphicsEllipseItem *ellipse = qgraphicsitem_cast<QGraphicsEllipseItem *>(item); // do something } else if (item->type() == MyItemSubclass::type()) { MyItemSubClass *myItem = qgraphicsitem_cast<MyItemSubClass *>(item); // do something } // etc } The above qgraphicsitem_cast could be replaced by static_cast since correct type is already verified. When doing lots of these all the time (very dynamic scene), will the numerous casting affect performance beyond the normal if-else evaluation?

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  • c# Wrapper to native c++ code, wrapping a parameter which is a pointer to an array

    - by mb300dturbo
    Hi, I have the following simple DLL in c++ un-managed code; extern "C" __declspec(dllexport) void ArrayMultiplier(float (*pointerArray)[3], int scalar, int length); void ArrayMultiplier(float (*pointerArray)[3], int scalar, int length) { for (int i = 0 ; i < length ; length++) { for (int j = 0; j < 3; j++) { pointerArray[i][j] = pointerArray[i][j] * scalar; } } } I have tried writing the following wrapper function for the above in c#: [DllImport("sample.dll")] public static extern void ArrayMultiplier(ref float elements, int scalar, int length); where elements is a 2 dimentional 3x3 array: public float[][] elements = { new float[] {2,5,3}, new float [] {4,8,6}, new float [] {5,28,3} }; The code given above compiles, but the program crashes when the wrapper function is called: Wrapper.ArrayMultiplier(ref elements, scalar, length); Please help me here, and tell me whats wrong with the code above, or how a wrapper can be written for a simple c++ function: void SimpleFunction(float (*pointerToArray)[3]); Thank you all in advance

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  • Changing pointer of self

    - by rob5408
    I have an object that I alloc/init like normal just to get a instance. Later in my application I want to load state from disk for that object. I figure I could unarchive my class (which conforms to NSCoding) and just swap where my instance points to. To this end I use this code... NSString* pathForDataFile = [self pathForDataFile]; if([[NSFileManager defaultManager] fileExistsAtPath:pathForDataFile] == YES) { NSLog(@"Save file exists"); NSData *data = [[NSMutableData alloc] initWithContentsOfFile:pathForDataFile]; NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data]; [data release]; Person *tempPerson = [unarchiver decodeObjectForKey:@"Person"]; [unarchiver finishDecoding]; [unarchiver release]; if (tempPerson) { [self release]; self = [tempPerson retain]; } } Now when I sprinkled some NSLogs throughout my application I noticed self.person: <Person: 0x3d01a10> (After I create the object with alloc/init) self: <Person: 0x3d01a10> (At the start of this method) tempPerson: <Person: 0x3b1b880> (When I create the tempPerson) self: <Person: 0x3b1b880> (after i point self to the location of the tempPerson) self.person: <Person: 0x3d01a10> (After the method back in the main program) What am I missing?

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  • dynimically using pointer

    - by gcc
    Input: 3 1 2 n 4 5 d 1 21 30 x Output: 2: 4 5 21 30 Input: 3 j 3 34 6 22 10 51 n 1 2 j 1 3 4 5 n 6 7 x Output: 1: 1 2 3 4 5 2: 6 7 3: 34 6 22 10 51 'j': (Jump to array# command) 'd': (Delete array# command) 'n': (Next array command) 'x': (Exit command) #: (Integer number) int num_arrays; /* maximum number of arrays */ int **arrays; /* array of array pointers */ int *l_arrays; /* actual lengths of arrays */ int *c_arrays; /* actual capacities of arrays */ how can we write that code

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  • Java: Using GSon incorrectly? (null pointer exception)

    - by Rosarch
    I'm trying to get the hits of a google search from a string of the query. public class Utils { public static int googleHits(String query) throws IOException { String googleAjax = "http://ajax.googleapis.com/ajax/services/search/web?v=1.0&q="; String json = stringOfUrl(googleAjax + query); JsonObject hits = new Gson().fromJson(json, JsonObject.class); return hits.get("estimatedResultCount").getAsInt(); } public static String stringOfUrl(String addr) throws IOException { ByteArrayOutputStream output = new ByteArrayOutputStream(); URL url = new URL(addr); IOUtils.copy(url.openStream(), output); return output.toString(); } public static void main(String[] args) throws URISyntaxException, IOException { System.out.println(googleHits("odp")); } } The following exception is thrown: Exception in thread "main" java.lang.NullPointerException at odp.compling.Utils.googleHits(Utils.java:48) at odp.compling.Utils.main(Utils.java:59) What am I doing incorrectly? Should I be defining an entire object for the Json return? That seems excessive, given that all I want to do is get one value. For reference: the returned JSON structure.

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  • Allocating memory for a char pointer that is part of a struct

    - by mrblippy
    hi, im trying to read in a word from a user, then dynamically allocate memory for the word and store it in a struct array that contains a char *. i keep getting a implicit declaration of function âstrlenâ so i know im going wrong somewhere. struct class { char class_code[4]; char *name; }; char buffer[101]; struct unit units[1000]; scanf("%s", buffer); units[0].name = (char *) malloc(strlen(buffer)+1); strcpy(units[0].name, buffer);

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