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  • Why is address zero used for null pointer?

    - by Joel
    In C (or C++ for that matter), pointers are special if they have the value zero: I am adviced to set pointers to zero after freeing their memory, because it means freeing the pointer again isn't dangerous; when I call malloc it returns a pointer with the value zero if it can't get me memory; I use if (p != 0) all the time to make sure passed pointers are valid etc. But since memory addressing starts at 0, isn't 0 just as a valid address as any other? How can 0 be used for handling null pointers if that is the case? Why isn't a negative number null instead?

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  • Freeing a character pointer returns error

    - by Kraffs
    I'm trying to free a character pointer after having used it but it returns a strange error. The error says: "_CrtDbgREport: String too long or IO Error" The debugger itself returns no errors while compiling. The code currently looks like this: void RespondToUser(SOCKET client, SOCKET server) { char buffer[80]; char *temp = malloc(_scprintf("HTTP/1.1 200 OK\r\n%s\r\nServer: %s\r\nConnection: close\r\n\r\nHi!", buffer, SERVER_NAME)); sprintf(temp, "HTTP/1.1 200 OK\r\n%s\r\nServer: %s\r\nConnection: close\r\n\r\nHi!", buffer, SERVER_NAME); send(client, temp, strlen(temp), 0); closesocket(client); free(temp); ListenToUsers(server); } The problem only occurs when I try to free the temp pointer from the memory and not otherwise. What might be causing this?

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  • Problem with pointer copy in C

    - by Stefano Salati
    I radically re-edited the question to explain better my application, as the xample I made up wasn't correct in many ways as you pointed out: I have one pointer to char and I want to copy it to another pointer and then add a NULL character at the end (in my real application, the first string is a const, so I cannot jsut modify it, that's why I need to copy it). I have this function, "MLSLSerialWriteBurst" which I have to fill with some code adapt to my microcontroller. tMLError MLSLSerialWriteBurst( unsigned char slaveAddr, unsigned char registerAddr, unsigned short length, const unsigned char *data ) { unsigned char *tmp_data; tmp_data = data; *(tmp_data+length) = NULL; // this function takes a tmp_data which is a char* terminated with a NULL character ('\0') if(EEPageWrite2(slaveAddr,registerAddr,tmp_data)==0) return ML_SUCCESS; else return ML_ERROR; } I see there's a problem here: tha fact that I do not initialize tmp_data, but I cannot know it's length.

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  • C pointer initialization and dereferencing, what's wrong here?

    - by randombits
    This should be super simple, but I'm not sure why the compiler is complaining here. #include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) { int *n = 5; printf ("n: %d", *n); exit(0); } Getting the following complaints: foo.c: In function ‘main’: foo.c:6: warning: initialization makes pointer from integer without a cast I just want to print the value that the pointer n references. I'm dereferencing it in the printf() statement and I get a segmentation fault. Compiling this with gcc -o foo foo.c.

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  • Null Pointer Exception with an array of bitsets

    - by p0ny
    could someone explain to me why the following results in a Null pointer Exception? And how to set a value for bitarray[0]? BitSet[] bitarray; bitarray= new BitSet[10]; bitarray[0].set(1); Also, why something like this work and not result in a pointer exception? BitSet[] bitarray = new BitSet[10]; BitSet bits = new BitSet(32); bits.set(1); bitarray[0] = bits; Thanks

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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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  • Referencing an array to a pointer

    - by james
    I want to refer a pointer to an array by another pointer. Example: void exp() { double var[2]; exp1(&var[0]); printf("\n varvalue is %lf\n",var[0]); } void exp1(double *var) { //updating the value *var[0]=4.0; exp2(&var[0]); } void exp2(double *var) { *var[0]=7.0; } This should update the value as 7.0(the last update).I am getting an array like invalid argument type of unary(*) . How can i correct this?where i am going wrong here?

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  • A pointer member variable having different values

    - by Rohan Prabhu
    Ok, to begin with, this is my code: HyperSprite::HyperSprite() { _view = 0; } void HyperSprite::publish(QGraphicsView* view) { _view = view; } void HyperSprite::getKFrame() { if(_view != 0) { qDebug()<<(void*)_view; } } Now, if I call HyperSprite::getKFrame() from within main(), I get the output: 0xbf8ffb84 I have a TCP server, which requires this QGraphicsView* variable. So whenever a new connection is made, HyperSprite::getKFrame() is called. However, whenever I make a connection to my server, this is the output: 0x1e425ff I honestly don't understand this. Shouldn't the value of a member remain same throughout? Why is the pointer value changing? As is obvious, whenever I try to use the _view pointer to access any of its members, a Segmentation Fault occurs. I tried using QSharedPointer, but it also results in the same problem. The data of the QSharedPointer automatically changes. Why is this happening?

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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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  • How to convert a void pointer to array of classes

    - by user99545
    I am trying to convert a void pointer to an array of classes in a callback function that only supports a void pointer as a means of passing paramaters to the callback. class person { std::string name, age; }; void callback (void *val) { for (int i = 0; i < 9; i++) { std::cout << (person [])val[i].name; } } int main() { person p[10]; callback((void*)p); } My goal is to be able to pass an array of the class person to the callback which then prints out the data such as their name and age. However, the compile does not like what I am doing and complains that error: request for member 'name' in 'val', which is of non-class type 'void*' How can I go about doing this?

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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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  • How to detect APC UPS battery usage and run a script when on battery

    - by Andy Arismendi
    I have a couple APC UPS - Smart-UPS RT 6000 RM XL Smart-UPS RT 5000 RM XL Unfortunately the power in my office likes to go out (out of my control) and hence the equipment powered by these UPS shuts down. They power a VMware infrastructure environment (VMware Lab Manager) and what I'd like to do is detect when one is on battery (say has been for x amount of time or has x percentage left) and run a script on this event. What software do I need to detect a on-battery event and have it run a script? Thanks!

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  • Installed Ubuntu 11.10, getting hard disk health warnings

    - by Brad
    I'm getting hard disk health problem warnings... When I click the "examine" button the disk utility pops up. None of my drives are reporting any major issues, and the very first drive doesn't even have a SMART button. I don't really care if one of the drives is crashing, I've got everything backed up, but I just want to know how to stop these god forsaken message boxes from popping up randomly. I have already gone into the Disk Utility and checked "do not notify me if this drive is failing" on all of them except the one that doesn't have the SMART button. I've googled about as much as I can for one day.

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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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  • 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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  • How to enforce users to create objects of class derived from mine with "new" only?

    - by sharptooth
    To implement reference counting we use an IUnknown-like interface and a smart pointer template class. The interface has implementation for all the reference-count methods, including Release(): void IUnknownLike::Release() { if( --refCount == 0 ) { delete this; } } The smart pointer template class has a copy constructor and an assignment operator both accepting raw pointers. So users can do the following: class Class : public IUnknownLike { }; void someFunction( CSmartPointer<Class> object ); //whatever function Class object; someFunction( &object ); and the program runs into undefined behavior - the object is created with reference count zero, the smart pointer is constructed and bumps it to one, then the function returns, smart pointer is destroyed, calls Release() which leads to delete of a stack-allocated variable. Users can as well do the following: struct COuter { //whatever else; Class inner;// IUnknownLike descendant }; COuter object; somefunction( &object.Inner ); and again an object not created with new is deleted. Undefined behavior at its best. Is there any way to change the IUnknownLike interface so that the user is forced to use new for creating all objects derived from IUnknownLike - both directly derived and indirectly derived (with classes in between the most derived and the base)?

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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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  • SmartView 11.1.2.2.103 - Support for MS Office 64 added

    - by THE
    Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 (thanks to Nancy, who shared this with me)  New for Smart View v11.1.2.2.103, Patch 14362638,   Microsoft Office 64-bit is now supported:  Information for 64-Bit Microsoft Office Installations: In this release, Smart View supports the 64-bit version on Microsoft Office. If you use 64-bit Office, please note the following: Oracle provides separate Smart View installation files for 64-bit and 32-bit Office systems. . smartview-x64.exe is the file for 64-bit Office installations. smartview.exe is the file for 32-bit Office installations. The 64-bit version of Smart View pertains only to the 64-bit version of Microsoft Office and not to the version of the operating system. Customers with 64-bit operating systems and the 32-bit version of Microsoft Office should install the 32-bit version of Smart View. You cannot install the 64-bit version of Smart View from EPM Workspace (13530466). Although Planning Offline is supported for 64-bit operating systems, it is not supported for 64-bit Smart View installations. If you use Planning Offline with Smart View, you must use the 32-bit version of Smart View and the 32-bit version of Microsoft Office. In 64-bit versions of Excel 2010 SP1, the presence of Smart View functions may cause Excel to terminate abruptly and may prevent Copy Data Point and Paste Data Point functions from working. This is a Microsoft issue, and a service request has been filed with Microsoft. Workaround: Until the Microsoft fix, use the 32-bit version of Smart View. (13606492) The Smart View function migration utility is not supported on 64-bit Office. (14342207) /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif";}

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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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