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• What is "null pointer assignment error"?

  - by sharptooth

  One of job interview questions on C pointer here is the following: what is null pointer assignment error? I've googled for a while and don't see any reasonable explanation. What is that? Trying to write through a null pointer? Something architecture- or environment-specific? What exactly is that error?

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• How to const declare the this pointer sent as parameter

  - by Tomas

  Hi, I want to const declare the this pointer received as an argument. static void Class::func(const OtherClass *otherClass) { // use otherClass pointer to read, but not write to it. } It is being called like this: void OtherClass::func() { Class::func(this); } This does not compile nad if i dont const declare the OtherClass pointer, I can change it. Thanks.

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• pointer to a pointer in a linked list

  - by user1596497

  I'm trying to set a linked list head through pointer to a pointer. I can see inside the function that the address of the head pointer is changing but as i return to the main progran it becomes NULL again. can someone tell me what I'm doing wrong ?? #include <stdio.h> #include <stdlib.h> typedef void(*fun_t)(int); typedef struct timer_t { int time; fun_t func; struct timer_t *next; }TIMER_T; void add_timer(int sec, fun_t func, TIMER_T *head); void run_timers(TIMER_T **head); void timer_func(int); int main(void) { TIMER_T *head = NULL; int time = 1; fun_t func = timer_func; while (time < 1000) { printf("\nCalling add_timer(time=%d, func=0x%x, head=0x%x)\n", time, func, &head); add_timer(time, func, head); time *= 2; } run_timers(&head); return 0; } void add_timer(int sec, fun_t func, TIMER_T *head) { TIMER_T ** ppScan=&head; TIMER_T *new_timer = NULL; new_timer = (TIMER_T*)malloc(sizeof(TIMER_T)); new_timer->time = sec; new_timer->func = func; new_timer->next = NULL; while((*ppScan != NULL) && (((**ppScan).time)<sec)) ppScan = &(*ppScan)->next; new_timer->next = *ppScan; *ppScan = new_timer; }

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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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• pointer as second argument instead of returning pointer?

  - by Tyler

  I noticed that it is a common idiom in C to accept an un-malloced pointer as a second argument instead of returning a pointer. Example: /*function prototype*/ void create_node(node_t* new_node, void* _val, int _type); /* implementation */ node_t* n; create_node(n, &someint, INT) Instead of /* function prototype */ node_t* create_node(void* _val, int _type) /* implementation */ node_t* n = create_node(&someint, INT) What are the advantages and/or disadvantages of both approaches? Thanks!

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• Base class pointer vs inherited class pointer?

  - by Goose Bumper

  Suppose I have a class Dog that inherits from a class Animal. What is the difference between these two lines of code? Animal *a = new Dog(); Dog *d = new Dog(); In one, the pointer is for the base class, and in the other, the pointer is for the derived class. But when would this distinction become important? For polymorphism, either one would work exactly the same, right?

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• Dereference a pointer inside a structure pointer

  - by klez

  I have a structure: struct mystruct { int* pointer; }; structure mystruct* struct_inst; Now I want to change the value pointed to by struct_inst->pointer. How can I do that?

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• IS NULL vs = NULL in where clause + SQL Server

  - by Nev_Rahd

  Hello How to check a value IS NULL [or] = @param (where @param is null) Ex: Select column1 from Table1 where column2 IS NULL => works fine If I want to replace comparing value (IS NULL) with @param. How can this be done Select column1 from Table1 where column2 = @param => this works fine until @param got some value in it and if is null never finds a record. How can this achieve?

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• IS NULL vs = NULL in where clause + MSSQL

  - by Nev_Rahd

  Hello How to check a value IS NULL [or] = @param (where @param is null) Ex: Select column1 from Table1 where column2 IS NULL = works fine If I want to replace comparing value (IS NULL) with @param. How can this be done Select column1 from Table1 where column2 = @param = this works fine until @param got some value in it and if is null never finds a record. How can this achieve?

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• How to check if a pointer is null in C++ Visual 2010

  - by mariomario

  I am having problems here if I want to check if eerste points to nothing i get Blockquote Unhandled exception at 0x003921c6 in Bank.exe: 0xC0000005: Access violation reading location 0xccccccd0. and i am kinda wondering why he justs skips the if statement or doens't stop when the object eerste points to nothing Bank::Bank() { LijstElement *eerste = NULL; LijstElement *laatste = NULL; } Rekening * Bank::getRekening(int rekNr) { if(NULL != eerste) { LijstElement *nummer = eerste; while(nummer->volgende!= NULL) { Rekening *een = nummer->getRekening(); if(een->getRekNr()==rekNr) { return een; } else { nummer = nummer->volgende; } } } return NULL; }

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• pointer-to-pointer of derived class in multiple inheritance

  - by Abdul jalil

  i have 3 classes A,B and C. C is derived from A and B. i get pointer to pointer of class C and cast to A** , and B ** , the variable that hold the the B** has the address of A** in my example B ** BdoublePtr hold the address of A** .i am using the following code #include "conio.h" #include "stdio.h" #include "string.h" class A{ public: A() { strA=new char[30]; strcpy(strA,"class A"); } char *strA; }; class B { public: B() { strB=new char[30]; strcpy(strB,"class B"); } char *strB; }; class C :public A, public B { public: C() { strC=new char[30]; strcpy(strC,"class C"); } char *strC; }; int main(void) { C* ptrC=new C(); A * Aptr=(A*)ptrC; printf("\n class A value : %s",Aptr-strA); B * Bptr=(B*)ptrC; printf("\n class B value :%s",Bptr-strB); printf("\n\nnow with double pointer "); A ** AdoublePtr=(A **)&ptrC; Aptr=AdoublePtr; printf("\n class A value : %s",Aptr-strA); B * BdoublePtr=(B **)&ptrC; Bptr=*BdoublePtr; printf("\n class B value : %s",Bptr-strB); getch(); return 0; }

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• C++, function pointer to the template function pointer

  - by Ian

  I am having a pointer to the common static method class MyClass { private: static double ( *pfunction ) ( const Object *, const Object *); ... }; pointing to the static method class SomeClass { public: static double getA ( const Object *o1, const Object *o2); ... }; Initialization: double ( *MyClass::pfunction ) ( const Object *o1, const Object *o2 ) = &SomeClass::getA; I would like to convert this pointer to the static template function pointer: template <class T> static T ( *pfunction ) ( const Object <T> *, const Object <T> *); //Compile error where: class SomeClass { public: template <class T> static double getA ( const Object <T> *o1, const Object <T> *o2); ... }; But there is some error... Thanks for your help...

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• inserting or updating values into null textboxes [closed]

  - by tanya

  this is my sql table structure create table cottonpurchase ( slipNo int null, purchasedate datetime, farmercode int , farmername varchar (100), villagename varchar (100), basicprice int null, premium int null, totalamountpaid int null, weight int null, totalamountbasic int null, totalamountpremium int null, Yeildestimates int null ) I want to fill in the null values in my sql with actual values and not leave them null but I want to do that from my winforms app form! But if I do that it just adds a new record when what I want is for it to update the record which has, for example, farmercode = 2, farmername = blaah, and so on. I also want to enter this in the same records as in farmercode = 2 and the corresponding corresponding basic price = ... , everytime i do it it ends up making a new record and not in the existing one.

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• Pointer initialization

  - by SoulBeaver

  Sorry if this question has been asked before. On my search through SO I didn't find one that asked what I wanted to know. Basically, when I have this: typedef struct node { int data; node *node; } *head; and do node *newItem = new node; I am under the impression that I am declaring and reserving space, but not defining, a pointer to struct node, is that correct? So when I do newItem->data = 100 and newItem->next = 0 I get confused. newItem = 0would declare what exactly? Both data and next? The object as a whole? I'm especially confused when I use typedef. Which part is the macro? I assume node because that's how I call it, but why do I need it? Finally, what happens when I do: node *temp; temp = new node; temp = head->next; head->next = newItem; newItem->next = temp; I mean, head-next is a pointer pointing to object newItem, so I assume not to newItem.data or next themselves. So how can I use an uninitialized pointer that I described above safely like here? is head now not pointing to an uninitialized pointer?

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• c program pointer

  - by sandy101

  Hello , I am trying some programs in c face a problem with this program #include<stdio.h> int main() { int a=9,*x; float b=3.6,*y; char c='a',*z; printf("the value is %d\n",a); printf("the value is %f\n",b); printf("the value is %c\n",c); x=&a; y=&b; z=&c; printf("%u\n",a); printf("%u\n",b); printf("%u\n",c); x++; y++; z++; printf("%u\n",a); printf("%u\n",b); printf("%u\n",c); return 0; } can any one tell me what is the problem with this and i also want to know that when in the above case if the pointer value is incremented then will it over write the previous value address as suppose that the value we got in the above program (without the increment in the pointer value )is 65524 65520 65519 and after the increment the value of the pointer is 65526(as 2 increment for the int ) 65524(as 4 increment for the float ) 65520(as 1 increment for the char variable ) then if in that case will the new pointer address overwrite the content of the previous address and what value be contained at the new address ......plz help

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• What is the use of Pointer to Pointer?

  - by hiral

  Why do we need a double pointer? What are some examples or use cases?

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• Sql Server Where Case Then Is Null Else Is Not Null

  - by Fabio Montezuma

  I have a procedure which receive a bit variable called @FL_FINALIZADA. If it is null or false I want to restrict my select to show only the rows that contain null DT_FINALIZACAO values. Otherwise I want to show the rows containing not null DT_FINALIZACAO values. Something like this: SELECT * FROM ... WHERE ... AND (OPE.DT_FINALIZACAO = CASE WHEN (@FL_FINALIZADA <> 1) THEN NULL END OR OPE.DT_FINALIZACAO IS NOT NULL) In this case I receive the message: None of the result expressions in a CASE specification can be NULL. How can I achieve this? Thanks in advance.

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• commands&creating pointer [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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• n & x commands&creating pointer&with using malloc [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 arrays[1] 3 4 5 42 arrays[2] 23 0 9 9 arrays[5] 3 9 9 another input 12 2 3 4 n n 2 3 4 n 12 3 x expected output arrays[1] 2 3 4 arrays[3] 2 3 4 arrays[4] 12 3 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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• Question on Pointer Arithmetic

  - by pws5068

  Heyy Everybody! I am trying to create a memory management system, so that a user can call myMalloc, a method I created. I have a linked list keeping track of my free memory. My problem is when I am attempting to find the end of a free bit in my linked list. I am attempting to add the size of the memory free in that section (which is in the linked list) to the pointer to the front of the free space, like this. void *tailEnd = previousPlace->head_ptr + ((previousPlace->size+1)*(sizeof(int)); I was hoping that this would give me a pointer to the end of that segment. However, I keep getting the warning: "pointer of type 'void*' used in arithmetic" Is there a better way of doing this? Thanks!

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• "Initializing" the pointer in the separate function in C

  - by pechenie

  I need to do a simple thing, which I used to do many times in Java, but I'm stuck in C (pure C, not C++). The situation looks like this: int *a; void initArray( int *arr ) { arr = malloc( sizeof( int ) * SIZE ); } int main() { initArray( a ); // a is NULL here! what to do?! return 0; } I have some "initializing" function, which SHOULD assign a given pointer to some allocated data (doesn't matter). How should I give a pointer to a function in order to this pointer will be modified, and then can be used further in the code (after that function call returns)? Thanx for help.

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• Ultrawingrid - how to display #1/1/1800# as blank ( as if null )

  - by Charles Hankey

  Ultrawingrid 9.2 VS2008 .net 3.5 My wingrid uses a bindingsource. All datetimes which are null in SQL Server are delivered to the bindingsource as #1/1/1800# I would like Ultrawingrid to display this date as blank as it would a null from source. Also, if the date is null in the grid ( i.e. blanked out ) I would like to update the data source to the date #1/1/1800# ( the framework takes care of getting that date back into the backend as a null ) This seems like it should be a trivial matter but I can find no documentation on just where to intervene so the grid will see a particular date as a null and save a null as a particular date. This is the direction I've been headed but I don't think either is the right place and I can't even get the syntax to work in the BeforeRowUpdate as I cannot see how to set a value that is passed to the data binding without setting the value of control itself, which I think has to remain null in order to display as blank Private Sub ugPropMaster_BeforeRowUpdate(ByVal sender As Object, ByVal e As _ Infragistics.Win.UltraWinGrid.CancelableRowEventArgs) Handles _ ugPropMaster.BeforeRowUpdate If e.Row.Cells.Item("Exdate").Value Is Nothing Then e.Row.Cells("Exdate").Value = CDate(#1/1/1800#) End If End Sub Private Sub ugPropMaster_InitializeRow(ByVal sender As Object, ByVal e As _ Infragistics.Win.UltraWinGrid.InitializeRowEventArgs) Handles _ ugPropMaster.InitializeRow If CDate(e.Row.Cells.Item("Exdate").Value) = CDate(#1/1/1800#) Then e.Row.Cells.Item("Exdate").Value = Nothing End If End Sub Guidance much appreciated

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• Setting pointee to NULL so any pointer pointing to that address is NULL

  - by idealistikz

  Rather than assigning a pointer to NULL, is there any way to set the location in memory the pointer is pointing to, to NULL so that any other pointer pointing to that location will be NULL?

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• Managed bean property value not set to null

  - by Vladimir

  Hi! I'm new to JSF, so this question might be strange. I have an inputText component's value bound to managed bean's property of type Float. I need to set property to null when inputText field is empty, not to 0 value. It's not done by default, so I added converter with the following method implemented: public Object getAsObject(FacesContext arg0, UIComponent arg1, String arg2) throws ConverterException { if (StringUtils.isEmpty(arg2)) { return null; } float result = Float.parseFloat(arg2); if (result == 0) { return null; } return result; } I registered converter, and assigned it to inputText component. I logged arg2 argument, and also logged return value from getAsObject method. By my log I can see that it returns null value. But, I also log setter property on backing bean and argument is 0 value, not null as expected. To be more precise, it is setter property is called twice, once with null argument, second time with 0 value argument. It still sets backing bean value to 0. How can I set value to null? Thanks in advance.

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• NULL pointer comparison fails

  - by Ilya

  Hello, I'm initializing in a class a pointer to be NULL. Afterwards I check if it is NULL in the same class. But it's not always 0x0. Sometimes it's 0x8 or 0xfeffffff or 0x3f800000 or 0x80 or other strange stuff. In most case the pointer is 0x0 but sometimes it gets altered somehow. I'm sure that I'm not changing it anywhere in my code. Is there a way it gets changed by "itself"? Here's my code: MeshObject::MeshObject() { mesh.vertexColors = NULL; } MeshObject::MeshObject(const MeshObject &_copyFromMe) { SimpleLog("vertexColors pointer: %p", _copyFromMe.mesh.vertexColors); if (_copyFromMe.mesh.vertexColors != NULL) { SimpleLog("vertexColors"); this->mesh.vertexColors = new tColor4i[_copyFromMe.mesh.vertexCount]; memcpy(this->mesh.vertexColors, _copyFromMe.mesh.vertexColors, _copyFromMe.mesh.vertexCount * sizeof(tColor4i) ); } } My application crashes, because vertexColors wasn't initialized and is being copied. However it is NULL and shouldn't be copied. Thanks.

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