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  • pointer to a structure in a nested structure

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

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  • How does compiler understand the pointer type?

    - by Narek
    How c++ compiler understands the pointer type? As I know pointer has a size equal to WORD of the OS (32 or 64). So does it store dome info in that 32(or 64) bits about type? Just because you can not have a pointer on one type and assign to that pointer another pointer with a different type.

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  • Property Scope (Iphone)

    - by Hank
    Hello All. I am having trouble accessing a declared property and I think I am missing something fundamental about the nature of properties and perhaps view controllers. Here's what I'm doing so far: declaring a property "myPhone" in a root view controller called RootViewController. grabbing a phone number from a modally presented people picker setting "myPhone" to the value from the people picker (from within shouldContinueAfterSelectingPerson of ABPeoplePickerNavigationController) trying to access "myPhone" from another modally presented view controller "myPhone" continues to NSLog to null despite trying every permutation of self.myPhone, super, RootViewController, etc. to try and access the value I set. What am I missing?

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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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  • Send copy of class to view class so it can render him? ( iPhone )

    - by Johannes Jensen
    I'm making a game for the iPhone, and I have a class called Robot. Then I have a class called View, which renders everything. I want to send a copy of my Robot, which I defined in my ViewController, and I send it to gameView (which is View *gameView), like this: robot = [Robot new]; [gameView setRobot: [robot copy]]; I tried to make a copy but that didn't work, I could also do it with a pointer to Robot (&robot) but sometimes it just crashes ? I tried this in my View.h @interface definition: @property (copy) Robot* robot; but I get the error /RobotsAdventure/Classes/View.h:24: error: setter '-robot' argument type does not match property type :/ Help? I'm pretty new at this, heh.

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  • Can a pointer ever point to itself?

    - by eSKay
    This question was mentioned here. My doubt is: If a pointer variable has the same address as its value, is it really pointing to itself? For example - in the following piece of code, is a a pointer to itself? #include<stdio.h> int main(){ int* a; int b = (int)&a; a = b; printf("address of a = %d\n", &a); printf(" value of a = %d\n", a); } If a is not a pointer to itself, then the same question poses again: Can a pointer point to itself? Also, how is a self pointing pointer useful?

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  • Can someone explain how pointer to pointer works?

    - by user3549560
    I don't really understand how the pointer to pointer works. Any way to do the same work without using pointer to pointer? struct customer{ char name[20]; char surname[20]; int code; float money; }; typedef struct customer customer; void inserts(customer **tmp) { *tmp = (customer*)malloc(sizeof(customer)); puts("Give me a customer name, surname code and money"); scanf("%s %s %d %f", (*tmp)->name, (*tmp)->surname, &(*tmp)->code,&(*tmp)->money); }

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  • C newbie malloc question

    - by roufamatic
    Why doesn't this print 5? void writeValue(int* value) { value = malloc(sizeof(int)); *value = 5; } int main(int argc, char * argv) { int* value = NULL; writeValue(value); printf("value = %d\n", *value); // error trying to access 0x00000000 } and how can I modify this so it would work while still using a pointer as an argument to writeValue?

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  • Storing Object Types in Variable then Initializing

    - by Jon Mattingly
    Is there a way in Objective-C to store an object/class in a variable to be passed to alloc/init somewhere else? For example: UIViewController = foo foo *bar = [[foo alloc] init] I'm trying to create a system to dynamically create navigation buttons in a separate class based on the current view controller. I can pass 'self' to the method, but the variable that results does not allow me to alloc/init. I could always import the .h file directly, but ideally I would like to make reusing the code as simple as possible. Maybe I'm going about this the wrong way?

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  • C++ multidimensional dynamic array

    - by dmessf
    Let's say I have this to create a multidimensional array dynamically: int* *grid = new int*[gridSizeX]; for (int i=0; i<gridSizeX; i++) { grid[i] = new int[gridSizeY]; } Shouldn't be possible now to access elements like grid[x][y] = 20?

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  • Alternates to C++ Reference/Pointer Syntax

    - by Jon Purdy
    What languages other than C and C++ have explicit reference and pointer type qualifiers? People seem to be easily confused by the right-to-left reading order of types, where char*& is "a reference to a pointer to a character", or a "character-pointer reference"; do any languages with explicit references make use of a left-to-right reading order, such as &*char/ref ptr char? I'm working on a little language project, and legibility is one of my key concerns. It seems to me that this is one of those questions to which it's easy for a person but hard for a search engine to provide an answer. Thanks in advance!

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  • Alternatives to C++ Reference/Pointer Syntax

    - by Jon Purdy
    What languages other than C and C++ have explicit reference and pointer type qualifiers? People seem to be easily confused by the right-to-left reading order of types, where char*& is "a reference to a pointer to a character", or a "character-pointer reference"; do any languages with explicit references make use of a left-to-right reading order, such as &*char/ref ptr char? I'm working on a little language project, and legibility is one of my key concerns. It seems to me that this is one of those questions to which it's easy for a person but hard for a search engine to provide an answer. Thanks in advance!

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  • Problem with Command Pattern under Visual Studio 2008 (C++)

    - by D.Giunchi
    Dear All, I've a problem with this pattern under c++ on VS 2008. The same code has been tested in gcc (linux, mac and mingw for widnows) and it works. I copy/paste the code here: class MyCommand { public: virtual void execute() = 0; virtual ~MyCommand () {}; }; class MyOperation { public: virtual void DoIt() {}; //I also write it not inline }; class MyOperationDerived : public MyOperation { public: virtual void DoIt() {}; //I also write it not inline }; class MyUndoStackCommand : public MyCommand { public: typedef void(MyOperation::*Action)(); MyUndoStackCommand(MyOperation *rec, Action action); /*virtual*/ void execute(); /*virtual*/ ~MyUndoStackCommand(); private: MyOperation *myReceiver; Action myAction ; }; in cpp: #include "MyUndoStackCommand.h" #include "MyOperation.h" MyUndoStackCommand::~MyUndoStackCommand() { } MyUndoStackCommand::MyUndoStackCommand(myOperation *rec, Action action): myReceiver(rec), myAction(action) { } void MyUndoStackCommand::execute() { ((myReceiver)->*(myAction))(); } use in main.cpp: MyReceiver receiver; MyUndoStackCommand usc(&receiver, &MyOperation::DoIt); usc.execute(); when I debug under visual studio only if I set inside MyUndoStackCommand, directly myAction = &MyOperation::DoIt , it works, otherwise not. Any advice? thank you very much, dan Edit: The following code compiles with g++ - changes by Neil Butterworth flagged as //NB. class MyCommand { public: virtual void execute() = 0; virtual ~MyCommand () {}; }; class MyOperation { public: virtual void DoIt() {}; //I also write it not inline }; class MyOperationDerived : public MyOperation { public: virtual void DoIt() {}; //I also write it not inline }; class MyUndoStackCommand : public MyCommand { public: typedef void(MyOperation::*Action)(); MyUndoStackCommand(MyOperation *rec, Action action); /*virtual*/ void execute(); /*virtual*/ ~MyUndoStackCommand(); private: MyOperation *myReceiver; Action myAction ; }; MyUndoStackCommand::~MyUndoStackCommand() { } MyUndoStackCommand::MyUndoStackCommand(MyOperation *rec, //NB Action action) : myReceiver(rec), myAction(action) { } void MyUndoStackCommand::execute() { ((myReceiver)->*(myAction))(); } int main() { MyOperation receiver; //NB MyUndoStackCommand usc(&receiver, &MyOperation::DoIt); usc.execute(); }

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  • Typcast a null pointer to char*

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

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  • Writing a printList method for a Scheme interpreter in C

    - by Rehan Rasool
    I am new to C and working on making an interpreter for Scheme. I am trying to get a suitable printList method to traverse through the structure. The program takes in an input like: (a (b c)) and internally represent it as: [""][ ][ ]--> [""][ ][/] | | ["A"][/][/] [""][ ][ ]--> [""][ ][/] | | ["B"][/][/] ["C"][/][/] Right now, I just want the program to take in the input, make the appropriate cell structure internally and print out the cell structure, thereby getting (a (b c)) at the end. Here is my struct: typedef struct conscell *List; struct conscell { char symbol; struct conscell *first; struct conscell *rest; }; void printList(char token[20]){ List current = S_Expression(token, 0); printf("("); printf("First Value? %c \n", current->first->symbol); printf("Second value? %c \n", current->rest->first->first->symbol); printf("Third value? %c \n", current->rest->first->rest->first->symbol); printf(")"); } In the main method, I get the first token and call: printList(token); I tested the values again for the sublists and I think it is working. However, I will need a method to traverse through the whole structure. Please look at my printList code again. The print calls are what I have to type, to manually get the (a (b c)) list values. So I get this output: First value? a First value? b First value? c It is what I want, but I want a method to do it using a loop, no matter how complex the structure is, also adding brackets where appropriate, so in the end, I should get: (a (b c)) which is the same as the input. Can anyone please help me with this?

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  • C++, using one byte to store two variables

    - by 2di
    Hi All I am working on representation of the chess board, and I am planning to store it in 32 bytes array, where each byte will be used to store two pieces. (That way only 4 bits are needed per piece) Doing it in that way, results in a overhead for accessing particular index of the board. Do you think that, this code can be optimised or completely different method of accessing indexes can be used? c++ char getPosition(unsigned char* c, int index){ //moving pointer c+=(index>>1); //odd number if (index & 1){ //taking right part return *c & 0xF; }else { //taking left part return *c>>4; } } void setValue(unsigned char* board, char value, int index){ //moving pointer board+=(index>>1); //odd number if (index & 1){ //replace right part //save left value only 4 bits *board = (*board & 0xF0) + value; }else { //replacing left part *board = (*board & 0xF) + (value<<4); } } int main() { char* c = (char*)malloc(32); for (int i = 0; i < 64 ; i++){ setValue((unsigned char*)c, i % 8,i); } for (int i = 0; i < 64 ; i++){ cout<<(int)getPosition((unsigned char*)c, i)<<" "; if (((i+1) % 8 == 0) && (i > 0)){ cout<<endl; } } return 0; } I am equally interested in your opinions regarding chess representations, and optimisation of the method above, as a stand alone problem. Thanks a lot

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  • pointer pointer

    - by gcc
    why we using double pointer like char **p; are there any purpose ,if there is please tell me i read some books but none of them tells purpose(s) of pointer to pointer if we can write char *p; and char **p; i think we may write char ***p; or char ****p; am i wrong

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  • NULL pointer dereference in C

    - by user554125
    hey ive got this piece of code. It dereferences a null pointer here. But then there is an and with unsigned int. I really dont understand the whole part. Can someone explain the output.?? struct hi { long a; int b; long c; }; int main() { struct hi ob={3,4,5}; struct hi *ptr=&ob; int num= (unsigned int) & (((struct hi *)0)->b); printf("%d",num); printf("%d",*(int *)((char *)ptr + (unsigned int) & (((struct hi *)0)->b))); } The o/p i get is 44 .But how does it work?

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