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• How to use shared_ptr for COM interface pointers

  - by Seefer

  I've been reading about various usage advice relating to the new c++ standard smart pointers unique_ptr, shared_ptr and weak_ptr and generally 'grok' what they are about when I'm writing my own code that declares and consumes them. However, all the discussions I've read seem restricted to this simple usage situation where the programmer is using smart in his/her own code, with no real discussion on techniques when having to work with libraries that expect raw pointers or other types of 'smart pointers' such as COM interface pointers. Specifically I'm learning my way through C++ by attempting to get a standard Win32 real-time game loop up and running that uses Direct2D & DirectWrite to render text to the display showing frames per second. My first task with Direct2D is in creating a Direct2D Factory object with the following code from the Direct2D examples on MSDN: ID2D1Factory* pD2DFactory = nullptr; HRESULT hr = D2D1CreateFactory(D2D1_FACTORY_TYPE_SINGLE_THREADED, &pD2DFactory); pD2DFactory is obviously an 'out' parameter and it's here where I become uncertain how to make use of smart pointers in this context, if indeed it's possible. My inexperienced C++ mind tells me I have two problems: With pD2DFactory being a COM interface pointer type, how would smart_ptr work with the Add() / Release() member functions for a COM object instance? Are smart pointers able to be passed to functions in situations where the function is using an 'out' pointer parameter technique? I did experiment with the alternative of using _com_ptr_t in the comip.h header file to help with pointer lifetime management and declared the pD2DFactory pointer with the following code: _com_ptr_t<_com_IIID<pD2DFactory, &__uuidof(pD2DFactory)>> pD2DFactory = nullptr; and it appears to work so far but, as you can see, the syntax is cumbersome :) So, I was wondering if any C++ gurus here could confirm whether smart pointers are able to help in cases like this and provide examples of usage, or point me to more in-depth discussions of smart pointer usage when needing to work with other code libraries that know nothing of them. Or is it simply a case of my trying to use the wrong tool for the job? :)

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• null != null - any ideas on how to re-arrange the code or prevent this?

  - by Alex

  Currently debugging, and found an if-statement which for no (I thought...) reason gave me an NPE, obviously for a reason. Which seemed to be that the statement turned out to be if(false && (null != null || null != Color)). if(destination != null && (destination.getPiece() != null || destination.getPiece().getColour() != pieceColour)) - the if-statement Both destination can be null and piece can be. The getColour() method returns an attribute of type Color from piece, which must be null if the piece is null. The piece at destination has a different pieceColour attribute then the one in the if-statement. Specifically, how do I re-arrange (destination.getPiece() != null) ?

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• Problem evaluating NULL in an IIF statement (Access)

  - by Mohgeroth

  Item in the recordset rstImportData("Flat Size") is = Null With that, given the following statement: IIF(IsNull(rstImportData("Flat Size")), Null, cstr(rstImportData("Flat Size"))) Result: Throws error 94: Invalid use of Null If I change the statement by removing the type conversion upon a false comparison: IIF(IsNull(rstImportData("Flat Size")), Null, 0) Result: Null It returns Null as it should have the first time. It appears that I cannot do a type conversion in an IIF if the value passed in should ever be null even if it passes an IIF test, it still attempts to evaluate it at both the true and false answer. The only reason I'm using IIF like this is because I have a 25 line comparison to compare data from an Import against a matching record in a database to see if I need to append the prior to history. Any thoughts? The way data is imported there will be null dates and where the spreadsheet import is in a string format I must convert either side to the other to compare the values properly but if either side is null this exception occurs :(

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• boost::serialization of mutual pointers

  - by KneLL

  First, please take a look at these code: class Key; class Door; class Key { public: int id; Door *pDoor; Key() : id(0), pDoor(NULL) {} private: friend class boost::serialization::access; template <typename A> void serialize(A &ar, const unsigned int ver) { ar & BOOST_SERIALIZATION_NVP(id) & BOOST_SERIALIZATION_NVP(pDoor); } }; class Door { public: int id; Key *pKey; Door() : id(0), pKey(NULL) {} private: friend class boost::serialization::access; template <typename A> void serialize(A &ar, const unsigned int ver) { ar & BOOST_SERIALIZATION_NVP(id) & BOOST_SERIALIZATION_NVP(pKey); } }; BOOST_CLASS_TRACKING(Key, track_selectively); BOOST_CLASS_TRACKING(Door, track_selectively); int main() { Key k1, k_in; Door d1, d_in; k1.id = 1; d1.id = 2; k1.pDoor = &d1; d1.pKey = &k1; // Save data { wofstream f1("test.xml"); boost::archive::xml_woarchive ar1(f1); // !!!!! (1) const Key *pK = &k1; const Door *pD = &d1; ar1 << BOOST_SERIALIZATION_NVP(pK) << BOOST_SERIALIZATION_NVP(pD); } // Load data { wifstream i1("test.xml"); boost::archive::xml_wiarchive ar1(i1); // !!!!! (2) A *pK = &k_in; B *pD = &d_in; // (2.1) //ar1 >> BOOST_SERIALIZATION_NVP(k_in) >> BOOST_SERIALIZATION_NVP(d_in); // (2.2) ar1 >> BOOST_SERIALIZATION_NVP(pK) >> BOOST_SERIALIZATION_NVP(pD); } } The first (1) is a simple question - is it possible to pass objects to archive without pointers? If simply pass objects 'as is' that boost throws exception about duplicated pointers. But I'm confused of creating pointers to save objects. The second (2) is a real trouble. If comment out string after (2.1) then boost will corectly load a first Key object (and init internal Door pointer pDoor), but will not init a second Door (d_in) object. After this I have an inited *k_in* object with valid pointer to Door and empty *d_in* object. If use string (2.2) then boost will create two Key and Door objects somewhere in memory and save addresses in pointers. But I want to have two objects *k_in* and *d_in*. So, if I copy a values of memory objects to local variables then I store only addresses, for example, I can write code after (2.2): d_in.id = pD->id; d_in.pKey = pD->pKey; But in this case I store only a pointer and memory object remains in memory and I cannot delete it, because *d_in.pKey* will be unvalid. And I cannot perform a deep copy with operator=(), because if I write code like this: Key &operator==(const Key &k) { if (this != &k) { id = k.id; // call to Door::operator=() that calls *pKey = *d.pKey and so on *pDoor = *k.pDoor; } return *this; } then I will get a something like recursion of operator=()s of Key and Door. How to implement proper serialization of such pointers?

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• Declaration, allocation and assignment of an array of pointers to function pointers

  - by manneorama

  Hello Stack Overflow! This is my first post, so please be gentle. I've been playing around with C from time to time in the past. Now I've gotten to the point where I've started a real project (a 2D graphics engine using SDL, but that's irrelevant for the question), to be able to say that I have some real C experience. Yesterday, while working on the event system, I ran into a problem which I couldn't solve. There's this typedef, //the void parameter is really an SDL_Event*. //but that is irrelevant for this question. typedef void (*event_callback)(void); which specifies the signature of a function to be called on engine events. I want to be able to support multiple event_callbacks, so an array of these callbacks would be an idea, but do not want to limit the amount of callbacks, so I need some sort of dynamic allocation. This is where the problem arose. My first attempt went like this: //initial size of callback vector static const int initial_vecsize = 32; //our event callback vector static event_callback* vec = 0; //size static unsigned int vecsize = 0; void register_event_callback(event_callback func) { if (!vec) __engine_allocate_vec(vec); vec[vecsize++] = func; //error here! } static void __engine_allocate_vec(engine_callback* vec) { vec = (engine_callback*) malloc(sizeof(engine_callback*) * initial_vecsize); } First of all, I have omitted some error checking as well as the code that reallocates the callback vector when the number of callbacks exceed the vector size. However, when I run this code, the program crashes as described in the code. I'm guessing segmentation fault but I can't be sure since no output is given. I'm also guessing that the error comes from a somewhat flawed understanding on how to declare and allocate an array of pointers to function pointers. Please Stack Overflow, guide me.

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• C++ arithmetic with pointers

  - by user69514

  I am trying to add the following: I have an array of double pointers call A. I have another array of double pointers call it B, and I have an unsigned int call it C. So I want to do: A[i] = B[i] - C; how do I do it? I did: A[i] = &B[i] - C; I don't think I am doing this correctly.

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• Getting my head around the practical applications of strong and weak pointers in Objective-C

  - by Chris Wilson

  I've just read the accepted excellent answer to this question that clarifies the conceptual differences between strong and weak pointers in Objective-C, and I'm still trying to understand the practical differences. I come from a C++ background where these concepts don't exist, and I'm having trouble figuring out where I would use one vs the other. Could someone please provide a practical example, using Objective-C code, that illustrates the different uses of strong and weak pointers?

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• Why no switch on pointers?

  - by meeselet

  For instance: #include <stdio.h> void why_cant_we_switch_him(void *ptr) { switch (ptr) { case NULL: printf("NULL!\n"); break; default: printf("%p!\n", ptr); break; } } int main(void) { void *foo = "toast"; why_cant_we_switch_him(foo); return 0; } gcc test.c -o test test.c: In function 'why_cant_we_switch_him': test.c:5: error: switch quantity not an integer test.c:6: error: pointers are not permitted as case values Just curious. Is this a technical limitation? EDIT People seem to think there is only one constant pointer expression. Is that is really true, though? For instance, here is a common paradigm in Objective-C (it is really only C aside from NSString, id and nil, which are merely a pointers, so it is still relevant — I just wanted to point out that there is, in fact, a common use for it, despite this being only a technical question): #include <stdio.h> #include <Foundation/Foundation.h> static NSString * const kMyConstantObject = @"Foo"; void why_cant_we_switch_him(id ptr) { switch (ptr) { case kMyConstantObject: // (Note that we are comparing pointers, not string values.) printf("We found him!\n"); break; case nil: printf("He appears to be nil (or NULL, whichever you prefer).\n"); break; default: printf("%p!\n", ptr); break; } } int main(void) { NSString *foo = @"toast"; why_cant_we_switch_him(foo); foo = kMyConstantObject; why_cant_we_switch_him(foo); return 0; } gcc test.c -o test -framework Foundation test.c: In function 'why_cant_we_switch_him': test.c:5: error: switch quantity not an integer test.c:6: error: pointers are not permitted as case values It appears that the reason is that switch only allows integral values (as the compiler warning said). So I suppose a better question would be to ask why this is the case? (though it is probably too late now.)

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• What are function pointers good for ?

  - by gramm

  Hi, I have trouble seing the utility of the function pointers. I guess it may be useful in some case (it exists, after all), but I can't think of a case where it's better or unavoidable to use a function pointer. Could you give some example of good use of function pointers (in C or C++)? Many thanks :)

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• What is the point of function pointers?

  - by gramm

  Hi, I have trouble seing the utility of the function pointers. I guess it may be useful in some cases (they exist, after all), but I can't think of a case where it's better or unavoidable to use a function pointer. Could you give some example of good use of function pointers (in C or C++)? Many thanks :)

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• use .net webbrowser control by multithread, throw "EXCEPTION code=ACCESS_VIOLATION"

  - by user1507827

  i want to make a console program to monitor a webpage's htmlsourcecode, because some of the page content are created by some javescript, so i have to use webbrowser control. like : View Generated Source (After AJAX/JavaScript) in C# my code is below: public class WebProcessor { public string GeneratedSource; public string URL ; public DateTime beginTime; public DateTime endTime; public object GetGeneratedHTML(object url) { URL = url.ToString(); try { Thread[] t = new Thread[10]; for (int i = 0; i < 10; i++) { t[i] = new Thread(new ThreadStart(WebBrowserThread)); t[i].SetApartmentState(ApartmentState.STA); t[i].Name = "Thread" + i.ToString(); t[i].Start(); //t[i].Join(); } } catch (Exception ex) { Console.WriteLine(ex.ToString()); } return GeneratedSource; } private void WebBrowserThread() { WebBrowser wb = new WebBrowser(); wb.ScriptErrorsSuppressed = true; wb.DocumentCompleted += new WebBrowserDocumentCompletedEventHandler( wb_DocumentCompleted); while(true ) { beginTime = DateTime.Now; wb.Navigate(URL); while (wb.ReadyState != WebBrowserReadyState.Complete) { Thread.Sleep(new Random().Next(10,100)); Application.DoEvents(); } } //wb.Dispose(); } private void wb_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e) { WebBrowser wb = (WebBrowser)sender; if (wb.ReadyState == WebBrowserReadyState.Complete) { GeneratedSource= wb.Document.Body.InnerHtml; endTime = DateTime.Now; Console.WriteLine("WebBrowser " + (endTime-beginTime).Milliseconds + Thread.CurrentThread.Name + wb.Document.Title); } } } when it run, after a while (20-50 times), it throw the exception like this EXCEPTION code=ACCESS_VIOLATION (null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(nul l)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(n ull)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null) (null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(null)(nul l)(null)BACKTRACE: 33 stack frames: #0 0x083dba8db0 at MatchExactGetIDsOfNames in mshtml.dll #1 0x0879f9b837 at StrongNameErrorInfo in mscorwks.dll #2 0x0879f9b8e3 at StrongNameErrorInfo in mscorwks.dll #3 0x0879f9b93a at StrongNameErrorInfo in mscorwks.dll #4 0x0879f9b9e0 at StrongNameErrorInfo in mscorwks.dll #5 0x0879f9b677 at StrongNameErrorInfo in mscorwks.dll #6 0x0879f9b785 at StrongNameErrorInfo in mscorwks.dll #7 0x0879f192a8 at InstallCustomModule in mscorwks.dll #8 0x0879f19444 at InstallCustomModule in mscorwks.dll #9 0x0879f194ab at InstallCustomModule in mscorwks.dll #10 0x0879fa6491 at StrongNameErrorInfo in mscorwks.dll #11 0x0879f44bcf at DllGetClassObjectInternal in mscorwks.dll #12 0x089bbafa at in #13 0x087b18cc10 at in System.Windows.Forms.ni.dll #14 0x087b91f4c1 at in System.Windows.Forms.ni.dll #15 0x08d00669 at in #16 0x08792d6e46 at in mscorlib.ni.dll #17 0x08792e02cf at in mscorlib.ni.dll #18 0x08792d6dc4 at in mscorlib.ni.dll #19 0x0879e71b4c at in mscorwks.dll #20 0x0879e896ce at in mscorwks.dll #21 0x0879e96ea9 at CoUninitializeEE in mscorwks.dll #22 0x0879e96edc at CoUninitializeEE in mscorwks.dll #23 0x0879e96efa at CoUninitializeEE in mscorwks.dll #24 0x0879f88357 at GetPrivateContextsPerfCounters in mscorwks.dll #25 0x0879e9cc8f at CoUninitializeEE in mscorwks.dll #26 0x0879e9cc2b at CoUninitializeEE in mscorwks.dll #27 0x0879e9cb51 at CoUninitializeEE in mscorwks.dll #28 0x0879e9ccdd at CoUninitializeEE in mscorwks.dll #29 0x0879f88128 at GetPrivateContextsPerfCounters in mscorwks.dll #30 0x0879f88202 at GetPrivateContextsPerfCounters in mscorwks.dll #31 0x0879f0e255 at InstallCustomModule in mscorwks.dll #32 0x087c80b729 at GetModuleFileNameA in KERNEL32.dll i have try lots of methods to solve the problem, finally, i found that if i thread sleep more millseconds, it will run for a longer time, but the exception is still throw. hope somebody give me the answer of how to slove ... thanks very much !!!

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• what is meant by normalization in huge pointers

  - by wrapperm

  Hi, I have a lot of confusion on understanding the difference between a "far" pointer and "huge" pointer, searched for it all over in google for a solution, couldnot find one. Can any one explain me the difference between the two. Also, what is the exact normalization concept related to huge pointers. Please donot give me the following or any similar answers: "The only difference between a far pointer and a huge pointer is that a huge pointer is normalized by the compiler. A normalized pointer is one that has as much of the address as possible in the segment, meaning that the offset is never larger than 15. A huge pointer is normalized only when pointer arithmetic is performed on it. It is not normalized when an assignment is made. You can cause it to be normalized without changing the value by incrementing and then decrementing it. The offset must be less than 16 because the segment can represent any value greater than or equal to 16 (e.g. Absolute address 0x17 in a normalized form would be 0001:0001. While a far pointer could address the absolute address 0x17 with 0000:0017, this is not a valid huge (normalized) pointer because the offset is greater than 0000F.). Huge pointers can also be incremented and decremented using arithmetic operators, but since they are normalized they will not wrap like far pointers." Here the normalization concept is not very well explained, or may be I'm unable to understand it very well. Can anyone try explaining this concept from a beginners point of view. Thanks, Rahamath

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• How do the operators < and > work with pointers?

  - by Øystein

  Just for fun, I had a std::list of const char*, each element pointing to a null-terminated text string, and ran a std::list::sort() on it. As it happens, it sort of (no pun intended) did not sort the strings. Considering that it was working on pointers, that makes sense. According to the documentation of std::list::sort(), it (by default) uses the operator < between the elements to compare. Forgetting about the list for a moment, my actual question is: How do these (, <, =, <=) operators work on pointers in C++ and C? Do they simply compare the actual memory addresses? char* p1 = (char*) 0xDAB0BC47; char* p2 = (char*) 0xBABEC475; e.g. on a 32-bit, little-endian system, p1 p2 because 0xDAB0BC47 0xBABEC475? Testing seems to confirm this, but I thought it'd be good to put it on StackOverflow for future reference. C and C++ both do some weird things to pointers, so you never really know...

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• converting mysql database to sql server

  - by every_answer_gets_a_point

  i have a mysql database: /* MySQL Data Transfer Source Host: 10.0.0.5 Source Database: jnetdata Target Host: 10.0.0.5 Target Database: jnetdata Date: 5/26/2009 12:27:33 PM */ SET FOREIGN_KEY_CHECKS=0; -- ---------------------------- -- Table structure for chavrusas -- ---------------------------- CREATE TABLE `chavrusas` ( `id` int(11) NOT NULL auto_increment, `date_created` datetime default NULL, `luser_id` int(11) default NULL, `ruser_id` int(11) default NULL, `luser_type` varchar(50) default NULL, `ruser_type` varchar(50) default NULL, `SessionDay` varchar(250) default NULL, `SessionTime` datetime default NULL, `WeeklyReminder` tinyint(1) NOT NULL default '0', `reminder_phone` tinyint(1) NOT NULL default '0', `calling_card` varchar(50) default NULL, `active` tinyint(1) NOT NULL default '0', `notes` mediumtext, `ended` tinyint(1) NOT NULL default '0', `end_date` datetime default NULL, `initiated_by_student` tinyint(1) NOT NULL default '0', `initiated_by_volunteer` tinyint(1) NOT NULL default '0', `student_general_reason` varchar(50) default NULL, `volunteer_general_reason` varchar(50) default NULL, `student_reason` varchar(250) default NULL, `volunteer_reason` varchar(250) default NULL, `student_nli` tinyint(1) NOT NULL default '0', `volunteer_nli` tinyint(1) NOT NULL default '0', `jnet_initiated` tinyint(1) default '0', `belongs_to` varchar(50) default NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM AUTO_INCREMENT=5913 DEFAULT CHARSET=latin1; -- ---------------------------- -- Table structure for tbluseravailability -- ---------------------------- CREATE TABLE `tbluseravailability` ( `availability_id` int(11) NOT NULL auto_increment, `user_id` int(11) NOT NULL, `weekday_id` int(11) NOT NULL, `timeslot_id` int(11) NOT NULL, PRIMARY KEY (`availability_id`) ) ENGINE=MyISAM AUTO_INCREMENT=10865 DEFAULT CHARSET=latin1; -- ---------------------------- -- Table structure for tblusers -- ---------------------------- CREATE TABLE `tblusers` ( `id` int(11) NOT NULL auto_increment, `password` varchar(50) default NULL, `title` varchar(255) default NULL, `first` varchar(255) default NULL, `last` varchar(255) default NULL, `gender` varchar(255) default NULL, `address` varchar(255) default NULL, `address_2` varchar(255) default NULL, `city` varchar(255) default NULL, `state` varchar(255) default NULL, `postcode` varchar(255) default NULL, `country` varchar(255) default NULL, `email` varchar(255) default NULL, `emailnotes` varchar(255) default NULL, `Home_Phone` varchar(255) default NULL, `Office_Phone` varchar(255) default NULL, `Cell_Phone` varchar(255) default NULL, `Contact_Preference` varchar(255) default NULL, `Birthdate` datetime default NULL, `Age` varchar(255 and it goes on for about 10mb i need to convert it to ms sql, how do i do it?

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• How to set arrayList size as null?

  - by Jessy

  String a []= {null,null,null,null,null}; //add array to arraylist ArrayList<Object> choice = new ArrayList<Object>(Arrays.asList(a)); System.out.println(choice.size()); Why the size of the arrayList choice is 5 when all the elements have been set to null

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• what is "=null" and " IS NULL"

  - by user329820

  I want some links for reading about the "=null" and "is null" please help me thanks

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• SQL SERVER – Validating Spatial Object as NULL using IsNULL

  - by pinaldave

  Follow up questions are the most fun part of writing a blog post. Earlier I wrote about SQL SERVER – Validating Spatial Object with IsValidDetailed Function and today I received a follow up question on the same subject. The question was mainly about how NULL is handled by spatial functions. Well, NULL is NULL. It is very easy to work with NULL. There are two different ways to validate if the passed in the value is NULL or not. 1) Using IsNULL Function IsNULL function validates if the object is null or not, if object is not null it will return you value 0 and if object is NULL it will return you the value NULL. DECLARE @p GEOMETRY = 'Polygon((2 2, 3 3, 4 4, 5 5, 6 6, 2 2))' SELECT @p.ISNULL ObjIsNull GO DECLARE @p GEOMETRY = NULL SELECT @p.ISNULL ObjIsNull GO 2) Using IsValidDetailed Function IsValidateDetails function validates if the object is valid or not. If the object is valid it will return 24400: Valid but if the object is not valid it will give message with the error number. In case object is NULL it will return the value as NULL. DECLARE @p GEOMETRY = 'Polygon((2 2, 3 3, 4 4, 5 5, 6 6, 2 2))' SELECT @p.IsValidDetailed() IsValid GO DECLARE @p GEOMETRY = NULL SELECT @p.IsValidDetailed() IsValid GO When to use what? Now you can see that there are two different ways to validate the NULL values. I personally have no preference about using one over another. However, there is one clear difference between them. In case of the IsValidDetailed Function the return value is nvarchar(max) and it is not always possible to compare the value with nvarchar(max). Whereas the ISNULL function returns the bit value of 0 when the object is null and it is easy to determine if the object is null or not in the case of ISNULL function. Additionally, ISNULL function does not check if the object is valid or not and will return the value 0 if the object is not NULL. Now you know even though either of the function can be used in place of each other both have very specific use case. Use the one which fits your business case. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Function, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: Spatial Database, SQL Spatial

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• Books on Pointers in C

  - by darkie15

  Hi All, Can anyone please recommend a good book (beginner, intermediate) for Pointers in C?? Regards, darkie15

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• What was that tutorial on pointers?

  - by pecker

  Hello, I once read a tutorial/article on Pointers somewhere. It was not a general tutorial but it explained how to clearly understand the complex & confusing pointers (especially like the ones that are usually asked in interview). It was more like http://www.codeweblog.com/right-left-rule-complex-pointer-analysis/ I'm unable to find it. Could any one post it here. PS: I did tried to google it but couldn't find. I'm asking it here because I thought it was popular.

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• Vector of Object Pointers, general help and confusion

  - by Staypuft

  Have a homework assignment in which I'm supposed to create a vector of pointers to objects Later on down the load, I'll be using inheritance/polymorphism to extend the class to include fees for two-day delivery, next day air, etc. However, that is not my concern right now. The final goal of the current program is to just print out every object's content in the vector (name & address) and find it's shipping cost (weight*cost). My Trouble is not with the logic, I'm just confused on few points related to objects/pointers/vectors in general. But first my code. I basically cut out everything that does not mater right now, int main, will have user input, but right now I hard-coded two examples. #include <iostream> #include <string> #include <vector> using namespace std; class Package { public: Package(); //default constructor Package(string d_name, string d_add, string d_zip, string d_city, string d_state, double c, double w); double calculateCost(double, double); void Print(); ~Package(); private: string dest_name; string dest_address; string dest_zip; string dest_city; string dest_state; double weight; double cost; }; Package::Package() { cout<<"Constucting Package Object with default values: "<<endl; string dest_name=""; string dest_address=""; string dest_zip=""; string dest_city=""; string dest_state=""; double weight=0; double cost=0; } Package::Package(string d_name, string d_add, string d_zip, string d_city, string d_state, string r_name, string r_add, string r_zip, string r_city, string r_state, double w, double c){ cout<<"Constucting Package Object with user defined values: "<<endl; string dest_name=d_name; string dest_address=d_add; string dest_zip=d_zip; string dest_city=d_city; string dest_state=d_state; double weight=w; double cost=c; } Package::~Package() { cout<<"Deconstructing Package Object!"<<endl; delete Package; } double Package::calculateCost(double x, double y){ return x+y; } int main(){ double cost=0; vector<Package*> shipment; cout<<"Enter Shipping Cost: "<<endl; cin>>cost; shipment.push_back(new Package("tom r","123 thunder road", "90210", "Red Bank", "NJ", cost, 10.5)); shipment.push_back(new Package ("Harry Potter","10 Madison Avenue", "55555", "New York", "NY", cost, 32.3)); return 0; } So my questions are: I'm told I have to use a vector of Object Pointers, not Objects. Why? My assignment calls for it specifically, but I'm also told it won't work otherwise. Where should I be creating this vector? Should it be part of my Package Class? How do I go about adding objects into it then? Do I need a copy constructor? Why? What's the proper way to deconstruct my vector of object pointers? Any help would be appreciated. I've searched for a lot of related articles on here and I realize that my program will have memory leaks. Using one of the specialized ptrs from boost:: will not be available for me to use. Right now, I'm more concerned with getting the foundation of my program built. That way I can actually get down to the functionality I need to create. Thanks.

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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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• C++ segmentation error when first parameter is null in comparison operator overload

  - by user1774515

  I am writing a class called Word, that handles a c string and overloads the <, , <=, = operators. word.h: friend bool operator<(const Word &a, const Word &b); word.cc: bool operator<(const Word &a, const Word &b) { if(a == NULL && b == NULL) return false; if(a == NULL) return true; if(b == NULL) return false; return a.wd < b.wd; //wd is a valid c string } main: char* temp = NULL; //EDIT: i was mistaken, temp is a char pointer Word a("blah"); //a.wd = [b,l,a,h] cout << (temp<a); i get a segmentation error before the first line of the operator< method after the last line in the main. I can correct the problem by writing cout << (a>temp); where the operator> is similarly defined and i get no errors. but my assignment requires (temp < a) to work so this is where i ask for help. EDIT: i made a mistake the first time and i said temp was of type Word, but it is actually of type char*. so i assume that the compiler converts temp to a Word using one of my constructors. i dont know which one it would use and why this would work since the first parameter is not Word. here is the constructor i think is being used to make the Word using temp: Word::Word(char* c, char* delimeters=NULL) { char *temporary = "\0"; if(c == NULL) c = temporary; check(stoppers!=NULL, "(Word(char*,char*))NULL pointer"); //exits the program if the expression is false if(strlen(c) == 0) size = DEFAULT_SIZE; //10 else size = strlen(c) + 1 + DEFAULT_SIZE; wd = new char[size]; check(wd!=NULL, "Word(char*,char*))heap overflow"); delimiters = new char[strlen(stoppers) + 1]; //EDIT: changed to [] check(delimiters!=NULL,"Word(char*,char*))heap overflow"); strcpy(wd,c); strcpy(delimiters,stoppers); count = strlen(wd); } wd is of type char* thanks for looking at this big question and trying to help. let me know if you need more code to look at

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• Dereferencing the null pointer

  - by zilgo

  The standard says that dereferencing the null pointer leads to undefined behaviour. But what is "the null pointer"? In the following code, what we call "the null pointer": struct X { static X* get() { return reinterpret_cast<X*>(1); } void f() { } }; int main() { X* x = 0; (*x).f(); // the null pointer? (1) x = X::get(); (*x).f(); // the null pointer? (2) x = reinterpret_cast<X*>( X::get() - X::get() ); (*x).f(); // the null pointer? (3) (*(X*)0).f(); // I think that this the only null pointer here (4) } My thought is that dereferencing of the null pointer takes place only in the last case. Am I right? Is there difference between compile time null pointers and runtime according to C++ Standard?

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• problem with network-manager-pptp

  - by Riuzaki90

  I've a problema with the VPA CAble connection of my university... on the website of the university there's a .sh file that set all the variables of the connection in ETC/PPP/PEERS and another .sh file that call the connection...I'm on ubuntu 11.10 and when I run the setup.sh I have this error: impossible to find network-manager-pptp these are the two file that I had talk about: #!/bin/bash echo "Creazione della connessione in corso attendere........." apt-get update apt-get install pptp-linux network-manager-pptp echo -n "Digitare la propria Username: " read USERNAME echo -n "Digitare la propria Password: " read PASSWORD pptpsetup --create UNICAL_Campus_Access --server 160.97.73.253 --username $USERNAME --password $PASSWORD echo 'pty "pptp 160.97.73.253 --nolaunchpppd"' >/etc/ppp/peers/UNICAL_Campus_Access echo 'require-mppe-128' >>/etc/ppp/peers/UNICAL_Campus_Access echo 'file /etc/ppp/options.pptp'>>/etc/ppp/peers/UNICAL_Campus_Access echo 'name '$USERNAME''>>/etc/ppp/peers/UNICAL_Campus_Access echo 'remotename PPTP'>>/etc/ppp/peers/UNICAL_Campus_Access echo 'ipparam UNICAL_Campus_Access'>>/etc/ppp/peers/UNICAL_Campus_Access echo $USERNAME' PPTP '$PASSWORD' *'>>/etc/ppp/chap-secrets rm /etc/ppp/options.pptp echo '###############################################################################'>/etc/ppp/options.pptp echo '# $Id: options.pptp,v 1.3 2006/03/26 23:11:05 quozl Exp $'>>/etc/ppp/options.pptp echo '#'>>/etc/ppp/options.pptp echo '# Sample PPTP PPP options file /etc/ppp/options.pptp'>>/etc/ppp/options.pptp echo '# Options used by PPP when a connection is made by a PPTP client.'>>/etc/ppp/options.pptp echo '# This file can be referred to by an /etc/ppp/peers file for the tunnel.'>>/etc/ppp/options.pptp echo '# Changes are effective on the next connection. See "man pppd".'>>/etc/ppp/options.pptp echo '#'>>/etc/ppp/options.pptp echo '# You are expected to change this file to suit your system. As'>>/etc/ppp/options.pptp echo '# packaged, it requires PPP 2.4.2 or later from http://ppp.samba.org/'>>/etc/ppp/options.pptp echo '# and the kernel MPPE module available from the CVS repository also on'>>/etc/ppp/options.pptp echo '# http://ppp.samba.org/, which is packaged for DKMS as kernel_ppp_mppe.'>>/etc/ppp/options.pptp echo '###############################################################################'>>/etc/ppp/options.pptp echo '# Lock the port'>>/etc/ppp/options.pptp echo 'lock'>>/etc/ppp/options.pptp echo '# Authentication'>>/etc/ppp/options.pptp echo '# We do not need the tunnel server to authenticate itself'>>/etc/ppp/options.pptp echo 'noauth'>>/etc/ppp/options.pptp echo '#We won"t do PAP, EAP, CHAP, or MSCHAP, but we will accept MSCHAP-V2'>>/etc/ppp/options.pptp echo '#(you may need to remove these refusals if the server is not using MPPE)'>>/etc/ppp/options.pptp echo 'refuse-pap'>>/etc/ppp/options.pptp echo 'refuse-eap'>>/etc/ppp/options.pptp echo 'refuse-chap'>>/etc/ppp/options.pptp echo 'refuse-mschap'>>/etc/ppp/options.pptp echo '# Compression Turn off compression protocols we know won"t be used'>>/etc/ppp/options.pptp echo 'nobsdcomp'>>/etc/ppp/options.pptp echo 'nodeflate'>>/etc/ppp/options.pptp echo '# Encryption'>>/etc/ppp/options.pptp echo '# (There have been multiple versions of PPP with encryption support,'>>/etc/ppp/options.pptp echo '# choose with of the following sections you will use. Note that MPPE'>>/etc/ppp/options.pptp echo '# requires the use of MSCHAP-V2 during authentication)'>>/etc/ppp/options.pptp echo '# http://ppp.samba.org/ the PPP project version of PPP by Paul Mackarras'>>/etc/ppp/options.pptp echo '# ppp-2.4.2 or later with MPPE only, kernel module ppp_mppe.o'>>/etc/ppp/options.pptp echo '#{{{'>>/etc/ppp/options.pptp echo '# Require MPPE 128-bit encryption'>>/etc/ppp/options.pptp echo '#require-mppe-128'>>/etc/ppp/options.pptp echo '#}}}'>>/etc/ppp/options.pptp echo '# http://polbox.com/h/hs001/ fork from PPP project by Jan Dubiec'>>/etc/ppp/options.pptp echo '#ppp-2.4.2 or later with MPPE and MPPC, kernel module ppp_mppe_mppc.o'>>/etc/ppp/options.pptp echo '#{{{'>>/etc/ppp/options.pptp echo '# Require MPPE 128-bit encryption'>>/etc/ppp/options.pptp echo '#mppe required,stateless'>>/etc/ppp/options.pptp echo '# }}}'>>/etc/ppp/options.pptp echo "setup di 'UNICAL Campus Access' terminato correttamente" echo "per connettersi eseguire lo script 'UNICAL_Campus_Access.sh' " and the second: #!/bin/bash echo "Connessione alla Rete del Centro Residenziale in corso attendere........." modprobe ppp_mppe pppd call UNICAL_Campus_Access sleep 30 tail -n 8 /var/log/messages echo "Connessione Stabilita" echo -n "Per terminare la connessione premere invio (in alternativa eseguire il commando 'killall pppd'):----> " read CONN killall pppd echo "Connessione terminata" I've correctly installed network-manager-pptp to the latest version...help?

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• sql query where parameters null not null

  - by Laziale

  I am trying to do a sql query and to build the where condition dynamically depending if the parameters are null or no. I have something like this: SELECT tblOrder.ProdOrder, tblOrder.Customer FROM tblOrder CASE WHEN @OrderId IS NOT NULL THEN WHERE tblOrder.OrderId = @OrderId ELSE END CASE WHEN @OrderCustomer IS NOT NULL THEN AND tblOrder.OrderCustomer = @OrderCustomer ELSE END END This doesn't work, but this is just a small prototype how to assemble the query, so if the orderid is not null include in the where clause, or if the ordercustomer is not null include in the where clause. But I see problem here, for example if the ordercustomer is not null but the orderid is null, there will be error because the where keyword is not included. Any advice how I can tackle this problem. Thanks in advance, Laziale

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