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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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  • How can I assign pointer member with long string?

    - by Nano HE
    Hi, When I did the practice below to erase my pointer member and assign new value to it. (*pMyPointer).member.erase(); (*pMyPointer).member.assign("Hello"); // Successfully Than I tried more... (*pMyPointer).member.erase(); (*pMyPointer).member.assign("Long Multi Lines Format String"); // How to? If the long multi lines string can't quote by double quoter, how to handle it. Thank you.

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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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  • system crash after declaring global object of the class

    - by coming out of void
    hi, i am very new to c++. i am getting system crash (not compilation error) in doing following: i am declaring global pointer of class. BGiftConfigFile *bgiftConfig; class BGiftConfigFile : public EftBarclaysGiftConfig { } in this class i am reading tags from xml file. it is crashing system when this pointer is used to retrieve value. i am doing coding for verifone terminal. int referenceSetting = bgiftConfig->getreferencesetting(); //system error getreferencesetting() is member fuction of class EftBarclaysGiftConfig i am confused about behavior of pointer in this case. i know i am doing something wrong but couldn't rectify it. When i declare one object of class locally it retrieves the value properly. BGiftConfigFile bgiftConfig1; int referenceSetting = bgiftConfig1->getreferencesetting(); //working But if i declare this object global it also crashes the system. i need to fetch values at different location in my code so i forced to use someting global. please suggest me how to rectify this problem.

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  • C++: why a self pointer of a struct automatically changes to void*

    - by Stone
    struct ptr{ int node; ptr *next; ptr(){} ptr(int _node, ptr *_next){ node=_node; next=_next; } }; struct list_t{ ptr *sht; int size; void push(int node){ size++; sht=new ptr(node,sht); } }shthead[100001], comp[200001], tree[200001]; The struct ptr is a smart pointer, be used as a linked list. But when I debug the code in gdb, I found that the ptr*'s were all converted to void*. GDB output: (gdb) pt ptr type = struct ptr { int node; void *next; public: ptr(void); ptr(int, void *); } However, I can still see the data of the struct if I covert them back to ptr* in gdb. What's the reason for this please?

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  • Accessing any structs members at run-time.

    - by jmgunn
    Is it possible to get access to an individual member of a struct or class without knowing the names of its member variables? I would like to do an "offsetof(struct, tyname)" without having the struct name or member variable name hard coded amoungst other things. thanks.

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  • List<MyClass*> & array question

    - by Nano HE
    Hi, Assuming a definition like this, list<MyCommand*> subList ... MyCommand* pCmd = (MyCommand*)(m_treeSM.GetItemData(node)); I tried these statements below, but failed. pCmd->subList[2] (pCmd->subList)[2] How can I get the array member values(such as subList[2]). I want to replace the value of subList[2] with other same type value. Thank you.

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  • Does this have anything to do with endian-ness?

    - by eSKay
    This piece of code: #include<stdio.h> void hello() { printf("hello\n"); } void bye() { printf("bye\n"); } int main() { printf("%p\n", hello); printf("%p\n", bye); return 0; } output on my machine: 0x80483f4 0x8048408 [second address is bigger in value] on Codepad 0x8048541 0x8048511 [second address is smaller in value] Does this have anything to do with endian-ness of the machines? If not, Why the difference in the ordering of the addresses? Also, Why the difference in the difference? 0x8048541 - 0x8048511 = 0x30 0x8048408 - 0x80483f4 = 0x14 Btw, I just checked. This code (taken from here) says that both the machines are Little-Endian #include<stdio.h> int main() { int num = 1; if(*(char *)&num == 1) printf("Little-Endian\n"); else printf("Big-Endian\n"); return 0; }

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  • how to write binary copy of structure array to file

    - by cerr
    I would like to write a binary image of a structure array to a binary file. I have tried this so far: #include <stdio.h> #include <string.h> #define NUM 256 const char *fname="binary.bin"; typedef struct foo_s { int intA; int intB; char string[20]; }foo_t; void main (void) { foo_t bar[NUM]; bar[0].intA = 10; bar[0].intB = 999; strcpy(bar[0].string,"Hello World!"); Save(bar); printf("%s written succesfully!\n",fname); } int Save(foo_t* pData) { FILE *pFile; int ptr = 0; int itr = 0; pFile = fopen(fname, "w"); if (pFile == NULL) { printf("couldn't open %s\n", fname); return; } for (itr = 0; itr<NUM; itr++) { for (ptr=0; ptr<sizeof(foo_t); ptr++) { fputc((unsigned char)*((&pData[itr])+ptr), pFile); } fclose(pFile); } } but the compiler is saying aggregate value used where an integer was expected fputc((unsigned char)*((&pData[itr])+ptr), pFile); and I don't quite understand why, what am I doing wrong? Thanks!

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  • Detect pointer arithmetics because of LARGEADDRESSAWARE

    - by Suma
    I would like to switch my application to LARGEADDRESSAWARE. One of issues to watch for is pointer arithmetic, as pointer difference can no longer be represented as signed 32b. Is there some way how to find automatically all instances of pointer subtraction in a large C++ project? If not, is there some "least effort" manual or semi-automatic method how to achieve this?

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  • I can't get that `bus error` to stop sucking.

    - by Koning Baard XIV
    I have this a class called PPString: PPString.h #ifndef __CPP_PPString #define __CPP_PPString #include "PPObject.h" class PPString : public PPObject { char *stringValue[]; public: char *pointerToCharString(); void setCharString(char *charString[]); void setCharString(const char charString[]); }; #endif PPString.cpp #include "PPString.h" char *PPString::pointerToCharString() { return *stringValue; } void PPString::setCharString(char *charString[]) { *stringValue = *charString; } void PPString::setCharString(const char charString[]) { *stringValue = (char *)charString; } I'm trying to set the stringValue using std::cin: main.cpp PPString myString; myString.setCharString("LOLZ"); std::cout << myString.pointerToCharString() << std::endl; char *aa[1000]; std::cin >> *aa; myString.setCharString(aa); std::cout << myString.pointerToCharString() << std::endl; The first one, which uses a const char works, but the second one, with a char doesn't, and I get this output: copy and paste from STDOUT LOLZ im entering a string now... Bus error where the second line is what I entered, followed by pressing the return key. Can anyone help me fixing this? Thanks...

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