Search Results

Search found 3255 results on 131 pages for 'pointers'.

Page 22/131 | < Previous Page | 18 19 20 21 22 23 24 25 26 27 28 29  | Next Page >

  • return an address of a double

    - by bks
    i'm having an issue understanding why the following works: void doubleAddr(double* source, double** dest) { *dest = source; } i get a pointer to a double and want to change the double that dest points to: //usage: int main() { double* num; double* dest; doubleAddr(num, &dest); return 0; } thanks in advance

    Read the article

  • C++ - passing references to boost::shared_ptr

    - by abigagli
    If I have a function that needs to work with a shared_ptr, wouldn't it be more efficient to pass it a reference to it (so to avoid copying the shared_ptr object)? What are the possible bad side effects? I envision two possible cases: 1) inside the function a copy is made of the argument, like in ClassA::take_copy_of_sp(boost::shared_ptr<foo> &sp) { ... m_sp_member=sp; //This will copy the object, incrementing refcount ... } 2) inside the function the argument is only used, like in Class::only_work_with_sp(boost::shared_ptr<foo> &sp) //Again, no copy here { ... sp->do_something(); ... } I can't see in both cases a good reason to pass the boost::shared_ptr by value instead of by reference. Passing by value would only "temporarily" increment the reference count due to the copying, and then decrement it when exiting the function scope. Am I overlooking something? Andrea. EDIT: Just to clarify, after reading several answers : I perfectly agree on the premature-optimization concerns, and I alwasy try to first-profile-then-work-on-the-hotspots. My question was more from a purely technical code-point-of-view, if you know what I mean.

    Read the article

  • Normal pointer vs Auto pointer (std::auto_ptr)

    - by AKN
    Code snippet (normal pointer) int *pi = new int; int i = 90; pi = &i; int k = *pi + 10; cout<<k<<endl; delete pi; [Output: 100] Code snippet (auto pointer) Case 1: std::auto_ptr<int> pi(new int); int i = 90; pi = &i; int k = *pi + 10; //Throws unhandled exception error at this point while debugging. cout<<k<<endl; //delete pi; (It deletes by itself when goes out of scope. So explicit 'delete' call not required) Case 2: std::auto_ptr<int> pi(new int); int i = 90; *pi = 90; int k = *pi + 10; cout<<k<<endl; [Output: 100] Can someone please tell why it failed to work for case 1?

    Read the article

  • What's wrong with my destructor?

    - by Ahmed Sharara
    // Sparse Array Assignment.cpp : Defines the entry point for the console application. // #include "stdafx.h" #include<iostream> using namespace std; struct node{ int row; int col; int value; node* next_in_row; node* next_in_col; }; class MultiLinkedListSparseArray { private: char *logfile; node** rowPtr; node** colPtr; // used in constructor node* find_node(node* out); node* ins_node(node* ins,int col); node* in_node(node* ins,node* z); node* get(node* in,int row,int col); bool exist(node* so,int row,int col); node* dummy; int rowd,cold; //add anything you need public: MultiLinkedListSparseArray(int rows, int cols); ~MultiLinkedListSparseArray(); void setCell(int row, int col, int value); int getCell(int row, int col); void display(); void log(char *s); void dump(); }; MultiLinkedListSparseArray::MultiLinkedListSparseArray(int rows,int cols){ rowPtr=new node* [rows+1]; colPtr=new node* [cols+1]; for(int n=0;n<=rows;n++) rowPtr[n]=NULL; for(int i=0;i<=cols;i++) colPtr[i]=NULL; rowd=rows;cold=cols; } MultiLinkedListSparseArray::~MultiLinkedListSparseArray(){ cout<<"array is deleted"<<endl; for(int i=rowd;i>=0;i--){ for(int j=cold;j>=0;j--){ if(exist(rowPtr[i],i,j)) delete get(rowPtr[i],i,j); } } // it stops in the last loop & doesnt show the done word cout<<"done"<<endl; delete [] rowPtr; delete [] colPtr; delete dummy; } void MultiLinkedListSparseArray::log(char *s){ logfile=s; } void MultiLinkedListSparseArray::setCell(int row,int col,int value){ if(exist(rowPtr[row],row,col)){ (*get(rowPtr[row],row,col)).value=value; } else{ if(rowPtr[row]==NULL){ rowPtr[row]=new node; (*rowPtr[row]).value=value; (*rowPtr[row]).row=row; (*rowPtr[row]).col=col; (*rowPtr[row]).next_in_row=NULL; (*rowPtr[row]).next_in_col=NULL; } else if((*find_node(rowPtr[row])).col<col){ node* out; out=find_node(rowPtr[row]); (*out).next_in_row=new node; (*((*out).next_in_row)).col=col; (*((*out).next_in_row)).row=row; (*((*out).next_in_row)).value=value; (*((*out).next_in_row)).next_in_row=NULL; } else if((*find_node(rowPtr[row])).col>col){ node* ins; ins=in_node(rowPtr[row],ins_node(rowPtr[row],col)); node* g=(*ins).next_in_row; (*ins).next_in_row=new node; (*((*ins).next_in_row)).col=col; (*(*ins).next_in_row).row=row; (*(*ins).next_in_row).value=value; (*(*ins).next_in_row).next_in_row=g; } } } int MultiLinkedListSparseArray::getCell(int row,int col){ return (*get(rowPtr[row],row,col)).value; } void MultiLinkedListSparseArray::display(){ for(int i=1;i<=5;i++){ for(int j=1;j<=5;j++){ if(exist(rowPtr[i],i,j)) cout<<(*get(rowPtr[i],i,j)).value<<" "; else cout<<"0"<<" "; } cout<<endl; } } node* MultiLinkedListSparseArray::find_node(node* out) { while((*out).next_in_row!=NULL) out=(*out).next_in_row; return out; } node* MultiLinkedListSparseArray::ins_node(node* ins,int col){ while(!((*ins).col>col)) ins=(*ins).next_in_row; return ins; } node* MultiLinkedListSparseArray::in_node(node* ins,node* z){ while((*ins).next_in_row!=z) ins=(*ins).next_in_col; return ins; } node* MultiLinkedListSparseArray::get(node* in,int row,int col){ dummy=new node; dummy->value=0; while((*in).col!=col){ if((*in).next_in_row==NULL){ return dummy; } in=(*in).next_in_row; } return in; } bool MultiLinkedListSparseArray::exist(node* so,int row,int col){ if(so==NULL) return false; else{ while((*so).col!=col){ if((*so).next_in_row==NULL) return false; else so=(*so).next_in_row; } return true; } }

    Read the article

  • [C] this code, its work fine and return what i want, but its hang before print it ??

    - by Rami Jarrar
    I make this program :: #include<stdio.h> char *raw_input(char *msg); main() { char *s; *s = *raw_input("Message Here Is: "); printf("Return Done.."); printf(s); } char *raw_input(char *msg){ char *d; printf("%s", msg); scanf("%s",&d); return d; } What this do is, it print my message and scan for input from the user, then print it,, but whats the problem in print the input from the user ???

    Read the article

  • Whats the problem with int *p=23;

    - by piemesons
    Yesterday in my interview I was asked this question. (At that time I was highly pressurized by so many abrupt questions). int *p; *p=23; printf('%d',*p); Is there any problem with this code? I explained him that you are trying to assign value to a pointer to whom memory is not allocated. But the way he reacted, it was like I am wrong. Although I got the job but after that he said Mohit think about this question again. I don't know what he was trying to say. Please let me know is there any problem in my answer?

    Read the article

  • Getting a seg fault, having trouble with classes and variables.

    - by celestialorb
    Ok, so I'm still learning the ropes of C++ here so I apologize if this is a simple mistake. I have this class: class RunFrame : public wxFrame { public: RunFrame(); void OnKey(wxKeyEvent& keyEvent); private: // Configuration variables. const wxString *title; const wxPoint *origin; const wxSize *size; const wxColour *background; const wxColour *foreground; const wxString *placeholder; // Control variables. wxTextCtrl *command; // Event table. DECLARE_EVENT_TABLE() }; ...then in the OnKey method I have this code: void RunFrame::OnKey(wxKeyEvent& keyEvent) { // Take the key and process it. if(WXK_RETURN == keyEvent.GetKeyCode()) { bool empty = command -> IsEmpty(); } // Propogate the event through. keyEvent.Skip(); } ...but my program keeps seg faulting when it reaches the line where I attempt to call the IsEmpty method from the command variable. My question is, "Why?" In the constructor of the RunFrame class I can seemingly call methods for the command variable in the same way I'm doing so in the OnKey method...and it compiles correctly, it just seg faults on me when it attempts to execute that line. Here is the code for the constructor if necessary: RunFrame::RunFrame() : wxFrame(NULL, wxID_ANY, wxT("DEFAULT"), wxDefaultPosition, wxDefaultSize, wxBORDER_NONE) { // Create the styling constants. title = new wxString(wxT("RUN")); origin = new wxPoint(0, 0); size = new wxSize(250, 25); background = new wxColour(33, 33, 33); foreground = new wxColour(255, 255, 255); placeholder = new wxString(wxT("command")); // Set the styling for the frame. this -> SetTitle(*title); this -> SetSize(*size); // Create the panel and attach the TextControl to it. wxPanel *panel = new wxPanel(this, wxID_ANY, *origin, *size, wxBORDER_NONE); // Create the text control and attach it to the panel. command = new wxTextCtrl(panel, wxID_ANY, *placeholder, *origin, *size); // Set the styling for the text control. command -> SetBackgroundColour(*background); command -> SetForegroundColour(*foreground); // Connect the key event to the text control. command -> Connect(wxEVT_CHAR, wxKeyEventHandler(RunFrame::OnKey)); // Set the focus to the command box. command -> SetFocus(); } Thanks in advance for any help you can give! Regards, celestialorb

    Read the article

  • declaring a 2D array of pointer objects

    - by Tyler Stennette
    I'm having a tough time figuring out how to instantiate a 2D array of pointer objects. Here is how I'm doing it: Pieces* chessBoard[9][9]; When I want to set it to an actual object pointer, I'm doing the following: chessBoard[1][1] = new Rook(p1Rook); Rook is a class that inherits attributes from the Pieces class and p1Rook is a char variable set to 'R'. This class also implements virtual functions (not pure virtual) from Pieces such as move() or getPiece() that are unique to the particular chess piece. However, when I compile my program, I get the following error: ChessBoard.cpp:69: error: expected type-specifier before ‘Rook’ ChessBoard.cpp:69: error: cannot convert ‘int*’ to ‘Pieces*’ in assignment Can someone please explain what I should change to get rid of this rather annoying persistent error? I would appreciate it.

    Read the article

  • C Programming: malloc() inside another function

    - by vikramtheone
    Hi Guys, I need help with malloc() inside another function. I'm passing a pointer and size to the function from my main() and I would like to allocate memory for that pointer dynamically using malloc() from inside that called function, but what I see is that.... the memory which is getting allocated is for the pointer declared withing my called function and not for the pointer which is inside the main(). How should I pass a pointer to a function and allocate memory for the passed pointer from inside the called function? Can anyone throw light on this? Help!!! Vikram I have written the following code and I get the output as shown below SOURCE: main() { unsigned char *input_image; unsigned int bmp_image_size = 262144; if(alloc_pixels(input_image, bmp_image_size)==NULL) printf("\nPoint2: Memory allocated: %d bytes",_msize(input_image)); else printf("\nPoint3: Memory not allocated"); } signed char alloc_pixels(unsigned char *ptr, unsigned int size) { signed char status = NO_ERROR; ptr = NULL; ptr = (unsigned char*)malloc(size); if(ptr== NULL) { status = ERROR; free(ptr); printf("\nERROR: Memory allocation did not complete successfully!"); } printf("\nPoint1: Memory allocated: %d bytes",_msize(ptr)); return status; } PROGRAM OUTPUT: Point1: Memory allocated ptr: 262144 bytes Point2: Memory allocated input_image: 0 bytes

    Read the article

  • Mutual class instances in C++

    - by SepiDev
    Hi guys. What is the issue with this code? Here we have two files: classA.h and classB.h classA.h: #ifndef _class_a_h_ #define _class_a_h_ #include "classB.h" class B; //???? class A { public: A() { ptr_b = new B(); //???? } virtual ~A() { if(ptr_b) delete ptr_b; //???? num_a = 0; } int num_a; B* ptr_b; //???? }; #endif //_class_a_h_ classB.h: #ifndef _class_b_h_ #define _class_b_h_ #include "classA.h" class A; //???? class B { public: B() { ptr_a = new A(); //???? num_b = 0; } virtual ~B() { if(ptr_a) delete ptr_a; //???? } int num_b; A* ptr_a; //???? }; #endif //_class_b_h_ when I try to compile it, the compiler (g++) says: classB.h: In constructor ‘B::B()’: classB.h:12: error: invalid use of incomplete type ‘struct A’ classB.h:6: error: forward declaration of ‘struct A’ classB.h: In destructor ‘virtual B::~B()’: classB.h:16: warning: possible problem detected in invocation of delete operator: classB.h:16: warning: invalid use of incomplete type ‘struct A’ classB.h:6: warning: forward declaration of ‘struct A’ classB.h:16: note: neither the destructor nor the class-specific operator delete will be called, even if they are declared when the class is defined.

    Read the article

  • Write pointer to file in C

    - by Sergey
    I have a stucture: typedef structure student { char *name; char *surname; int age; } Student; I need to write it to binary file. Student *s = malloc(sizeof(*s)); I fill my structure with data and then i write in to the file: fwrite(s, sizeof(*s), 1, fp); In my file doesnt exist a name and surname, it have an adresses of char*. How can i write to file a word, not an adresses?

    Read the article

  • handling pointer to member functions within hierachy in C++

    - by anatoli
    Hi, I'm trying to code the following situation: I have a base class providing a framework for handling events. I'm trying to use an array of pointer-to-member-functions for that. It goes as following: class EH { // EventHandler virtual void something(); // just to make sure we get RTTI public: typedef void (EH::*func_t)(); protected: func_t funcs_d[10]; protected: void register_handler(int event_num, func_t f) { funcs_d[event_num] = f; } public: void handle_event(int event_num) { (this->*(funcs_d[event_num]))(); } }; Then the users are supposed to derive other classes from this one and provide handlers: class DEH : public EH { public: typedef void (DEH::*func_t)(); void handle_event_5(); DEH() { func_t f5 = &DEH::handle_event_5; register_handler(5, f5); // doesn't compile ........ } }; This code wouldn't compile, since DEH::func_t cannot be converted to EH::func_t. It makes perfect sense to me. In my case the conversion is safe since the object under this is really DEH. So I'd like to have something like that: void EH::DEH_handle_event_5_wrapper() { DEH *p = dynamic_cast<DEH *>(this); assert(p != NULL); p->handle_event_5(); } and then instead of func_t f5 = &DEH::handle_event_5; register_handler(5, f5); // doesn't compile in DEH::DEH() put register_handler(5, &EH::DEH_handle_event_5_wrapper); So, finally the question (took me long enough...): Is there a way to create those wrappers (like EH::DEH_handle_event_5_wrapper) automatically? Or to do something similar? What other solutions to this situation are out there? Thanks.

    Read the article

  • error: invalid type argument of '->' (have 'struct node')

    - by Roshan S.A
    Why cant i access the pointer "Cells" like an array ? i have allocated the appropriate memory why wont it act like an array here? it works like an array for a pointer of basic data types. #include<stdio.h> #include<stdlib.h> #include<ctype.h> #define MAX 10 struct node { int e; struct node *next; }; typedef struct node *List; typedef struct node *Position; struct Hashtable { int Tablesize; List Cells; }; typedef struct Hashtable *HashT; HashT Initialize(int SIZE,HashT H) { int i; H=(HashT)malloc(sizeof(struct Hashtable)); if(H!=NULL) { H->Tablesize=SIZE; printf("\n\t%d",H->Tablesize); H->Cells=(List)malloc(sizeof(struct node)* H->Tablesize); should it not act like an array from here on? if(H->Cells!=NULL) { for(i=0;i<H->Tablesize;i++) the following lines are the ones that throw the error { H->Cells[i]->next=NULL; H->Cells[i]->e=i; printf("\n %d",H->Cells[i]->e); } } } else printf("\nError!Out of Space"); } int main() { HashT H; H=Initialize(10,H); return 0; } The error I get is as in the title-error: invalid type argument of '->' (have 'struct node').

    Read the article

  • Pointer arithmetic.

    - by Knowing me knowing you
    Having code: int** a = new int*[2]; a[0] = new int(1); a[1] = new int(2); cout << "a[0] " << a[0] << '\n'; cout << "a[1] " << a[1] << '\n'; cout << "a[2] " << a[2] << '\n'; cout << "a[0] + 1 " << a[0] + 1 << '\n';//WHY THIS ISN'T == a[1] ? cout << "*(a + 1): " << *(a + 1) << '\n'; //WHY THIS IS == a[1] ? cout << "a[0] - a[1] " << static_cast<int>(a[0] - a[1])<< '\n';//WHY THIS IS == 16 not 4? cout << sizeof(int**); Questions are included right next to relevant lines in code.

    Read the article

  • Help with data retrieval MACRO

    - by Andrei Ciobanu
    Hello, given the following structure: struct nmslist_elem_s { nmptr data; struct nmslist_elem_s *next; }; typedef struct nmslist_elem_s nmslist_elem; Where: typedef void* nmptr; Is it possible to write a MACRO that retrieves the data from the element and cast it to the right type: MACRO(type, element) that expands to *((type*)element->data). For example for int, i would need something like this: *((int*)(element->data)) .

    Read the article

  • Passing pointer into function, data appears initialized in function, on return appears uninitialize

    - by Luke Mcneice
    Im passing function GetCurrentDate() the pointer to a tm struct. Within that function I printf the uninitialized data, then the initialized. Expected results. However when i return the tm struct appears uninitialized. See console output bellow. What am i doing wrong? uninitialized date:??? ???-1073908332 01:9448278:-1073908376 -1217355836 initialized date:Wed May 5 23:08:40 2010 Caller date:??? ???-1073908332 01:9448278:-1073908376 -121735583 int main() { test(); } int test() { struct tm* CurrentDate; GetCurrentDate(CurrentDate); printf("Caller date:%s\n",asctime (CurrentDate)); return 1; } int GetCurrentDate(struct tm* p_ReturnDate) { printf("uninitialized date:%s\n",asctime (p_ReturnDate)); time_t m_TimeEntity; m_TimeEntity = time(NULL); //setting current time into a time_t struct p_ReturnDate = localtime(&m_TimeEntity); //converting time_t to tm struct printf("initialized date:%s\n",asctime (p_ReturnDate)); return 1; }

    Read the article

  • Create thread is not accepting the member functon

    - by prabhakaran
    I am trying to create a class for network programming. This will create a general purpose socket with thread. But when I tried to creat the thread using createthread(). The third argument is producing errors. And from the net I came to know that I can't use the member functions as a argument to the createthread(). Is there any thing by which I can achieve this.

    Read the article

  • Passing a 2D array to a function in C

    - by Tyler Treat
    I have, essentially, a matrix of data (lets say ints) that I would like to store in a 2D array in which the dimensions are not known until runtime (say x columns and y rows). I want to populate the array in a function, so I assume I need to do something like this: int main(int argc, char **argv) { int y = atoi(argv[1]); int x = atoi(argv[2]); int **matrix = malloc(x * sizeof(int*)); populateMatrix(matrix, y, x); return 0; } void populateMatrix(**matrix, int y, int x) { int i, j; for (i = 0; i < y; i++) { for (j = 0; j < x; j++) { matrix[i][j] = i * j; // populated with trivial data to keep it simple } } } Obviously this doesn't work, but I'm not sure how to do what I'm describing exactly.

    Read the article

  • Forked Function not assigning pointer

    - by Luke Mcneice
    In the code below I have a function int GetTempString(char Query[]); calling it in main works fine. However, when calling the function from a fork the fork hangs (stops running, no errors, no output) before this line: pch = strtok (Query," ,"); the printf shows that the pointer to pch is null. Again this only happens when the fork is executing it. What am I doing doing wrong? int main() { if((Timer =fork())==-1) printf("Timer Fork Failed"); else if(Timer==0) { while(1) { sleep(2); GetTempString("ch 1,2,3,4"); } } else { //CODE GetTempString("ch 1,2,3,4"); } } int GetTempString(char Query[]) { char * pch; printf("DEBUG: '%s'-'%d'\n",Query,pch); pch = strtok (Query," ,");//* PROBLEM HERE* //while loop for strtok... return 1; }

    Read the article

  • Passing a template func. as a func. ptr to an overloaded func. - is there a way to compile this code

    - by LoudNPossiblyRight
    Just a general c++ curiosity: This code below shouldn't compile because it's impossible to know which to instantiate: temp(const int&) or temp(const string&) when calling func(temp) - this part i know. What i would like to know is if there is anything i can do to the line marked PASSINGLINE to get the compiler to deduce that i want FPTR1 called and not FPTR2 ? #include<iostream> using std::cout; using std::endl; /*FPTR1*/ void func(void(*fptr)(const int&)){ fptr(1001001);} /*FPTR2*/ void func(void(*fptr)(const string&)){ fptr("1001001"); } template <typename T> void temp(const T &t){ cout << t << endl; } int main(){ /*PASSINGLINE*/ func(temp); return 0; } Thank you.

    Read the article

  • how to cast c++ smart pointer up and down

    - by user217428
    two clients communicate to each other on top of a message layer in the message body, I need include a field pointing to any data type From client A, I send the field as a shared_ptr to the message layer. I define this field as a shared_ptr in the message layer. But how can I convert this field back to shared_ptr in client B? Or should I define shared_ptr in message layer as something else? Thanks

    Read the article

< Previous Page | 18 19 20 21 22 23 24 25 26 27 28 29  | Next Page >