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  • question regarding "this" pointer in c++

    - by sil3nt
    hello there, i have been given class with int variables x and y in private, and an operator overload function, class Bag{ private: int x; int y; public: Bag(); ~Bag(); //....... //.....etc }; Bag operator+ (Bag new) const{ Bag result(*this); //what does this mean? result.x += new.x; result.y += new.y; } What is the effect of having "Bag result(*this);" there?.

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  • C/C++ opaque pointer library

    - by aaa
    hello Is there library/header already written to manage C++ objects from C using opaque pointers/handles? I can write one myself, but I would rather use already made solution, especially if it has fortran bindings. Thanks

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  • Why do I get a Null Pointer Exception?

    - by Roman
    I have this code: Manager manager = new Manager("Name"); MyWindowListener windowListener = new MyWindowListener(); manager.addWindowListener(windowListener); Eclipse writes that I have a NullPointerException in the last line. What can be the reason for that. I do have constructors in the Manager and MyWindowListener. If it's important MyWindowListener implements WindowListener.

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  • Doubt regarding usage of array as a pointer in C

    - by Som
    For eg. I have an array of structs 'a' as below: struct mystruct{ int b int num; }; struct bigger_struct { struct my_struct a[10]; } struct bigger_struct *some_var; i know that the name of an array when used as a value implicitly refers to the address of the first element of the array.(Which is how the array subscript operator works at-least) Can i know do the other way around i.e if i do: some_var->a->b, it should be equivalent to some_var->a[0]->b, am i right? I have tested this and it seems to work , but is this semantically 100% correct?

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  • Obtaining frame pointer in C

    - by assketchum
    I'm trying to get the FP in my C program, I tried two different ways, but they both differ from what I get when I run GDB. The first way I tried, I made a protocol function in C for the Assembly function: int* getEbp(); and my code looks like this: int* ebp = getEbp(); printf("ebp: %08x\n", ebp); // value i get here is 0xbfe2db58 while( esp <= ebp ) esp -= 4; printf( "ebp: %08x, esp" ); //value i get here is 0xbfe2daec My assembly code getEbp: movl %ebp, %eax ret I tried making the prototype function to just return an int, but that also doesn't match up with my GDB output. We are using x86 assembly. EDIT: typos, and my getEsp function looks exactly like the other one: getEsp: movl %esp, %eax ret

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  • Extract inputs from a pointer to array of characters in C / C++

    - by user2066884
    I am writing a command line utility but I cannot find a way to store the commands and arguments. so far I have the following but I get a Segmentation fault: int main(void) { char *command; char *args[MAX_LINE/2 + 1]; int should_run = 1; do{ cout << "cmd> "; int counter = 0; while(cin >> command) { strcpy(args[counter],command); counter++; } cout << args[0] << "\n"; } }

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  • Changing Value of Array Pointer When Passed to a Function

    - by ZAX
    I have a function which receives both the array, and a specific instance of the array. I try to change the specific instance of the array by accessing one of its members "color", but it does not actually change it, as can be seen by debugging (checking the value of color after function runs in the main program). I am hoping someone can help me to access this member and change it. Essentially I need the instance of the array I'm specifying to be passed by reference if nothing else, but I'm hoping there is an easier way to accomplish what I'm trying to do. Here's the structures: typedef struct adjEdge{ int vertex; struct adjEdge *next; } adjEdge; typedef struct vertex{ int sink; int source; int color; //0 will be white, 1 will be grey, 5 will be black int number; adjEdge *nextVertex; } vertex; And here is the function: void walk(vertex *vertexArray, vertex v, int source, maxPairing *head) { int i; adjEdge *traverse; int moveVertex; int sink; traverse = vertexArray[v.number-1].nextVertex; if(v.color != 5 && v.sink == 5) { sink = v.number; v.color = 5; addMaxPair(head, source, sink); } else { walk(vertexArray, vertexArray[traverse->vertex-1], source, head); } } In particular, v.color needs to be changed to a 5, that way later after recursion the if condition blocks it.

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  • cant figure out pointer assignment in c

    - by vadiklk
    int add(char *var1, char *var2, char **var3) { int num1, num2, length1 = strlen(var1), length2 = strlen(var2), length = max(length1, length2) + 1; char *result = (char*) calloc(length, sizeof(char)); ... free(*var3); *var3 = result; return 0; } out side of the function i get its still nothing(var3); more detail: int addSubCommand(char **vars, int isAdd) { ... return add(vars[index1], var2, &(vars[index3])); } that's where i call add. the char** vars goes from every function to the other.

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  • Is there performance to be gained by moving storage allocation local to a member function to its cla

    - by neuviemeporte
    Suppose I have the following C++ class: class Foo { double bar(double sth); }; double Foo::bar(double sth) { double a,b,c,d,e,f a = b = c = d = e = f = 0; /* do stuff with a..f and sth */ } The function bar() will be called millions of times in a loop. Obviously, each time it's called, the variables a..f have to be allocated. Will I gain any performance by making the variables a..f members of the Foo class and just initializing them at the function's point of entry? On the other hand, the values of a..f will be dereferenced through this-, so I'm wondering if it isn't actually a possible performance degradation. Is there any overhead to accessing a value through a pointer? Thanks!

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  • How do I output an individual character when using char *[] = "something"

    - by Matt
    I've been playing with pointers to better understand them and I came across something I think I should be able to do, but can't sort out how. The code below works fine - I can output "a", "dog", "socks", and "pants" - but what if I wanted to just output the 'o' from "socks"? How would I do that? char *mars[4] = { "a", "dog", "sock", "pants" }; for ( int counter = 0; counter < 4; counter++ ) { cout << mars[ counter ]; } Please forgive me if the question is answered somewhere - there are 30+ pages of C++ pointer related question, and I spent about 90 minutes looking through them, as well as reading various (very informative) articles, before deciding to ask.

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  • C++ object in memory

    - by Neo_b
    Hello. Is there a standard in storing a C++ objects in memory? I wish to set a char* pointer to a certain address in memory, so that I can read certain objects' variables directly from the memory byte by byte. When I am using Dev C++, the variables are stored one by one right in the memory address of an object in the order that they were defined. Now, can it be different while using a different compiler (like the variables being in a different order, or somewhere else)? Thank you in advance. :-)

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  • fill a buffer successively

    - by mkind
    i intend to fill a char-pointer array successively in a for-loop. the content to fill in is a integer so i need to cast. but i didn't get the result i want to.. for (i=0;i<max0;i++){ sprintf(buf, "%d", content[i]); } sprintf replaces the hole buf, but i want to append. for (i=0;i<max0;i++){ buf[i]=(char) contint[i] } but this isn't working too. it seems to me, i get ascii-code of the content[i].

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  • C++ How do you set an array of pointers to null in an initialiser list like way?

    - by boredjoe
    I am aware you cannot use an initialiser list for an array. However I have heard of ways that you can set an array of pointers to NULL in a way that is similar to an initialiser list. I am not certain how this is done. I have heard that a pointer is set to NULL by default, though I do not know if this is guaranteed/ in the C++ standard. I am also not sure if initialising through the new operator compared to normal allocation can make a difference too.

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  • Cannot determine why pointer variable will not address elements in a string in this program?

    - by Smith Will Suffice
    I am attempting to utilize a pointer variable to access elements of a string and there are issues with my code generating a compilation error: #include <stdio.h> #define MAX 29 char arrayI[250]; char *ptr; int main(void) { ptr = arrayI; puts("Enter string to arrayI: up to 29 chars:\n"); fgets(arrayI, MAX, stdin); printf("\n Now printing array by pointer:\n"); printf("%s", *ptr); ptr = arrayI[1]; //(I set the pointer to the second array char element) printf("%c", *ptr); //Here is where I was wanting to use my pointer to //point to individual array elements. return 0; } My compiler crieth: [Warning] assignment makes pointer from integer without a cast [enabled by default] I do not see where my pointer was ever assigned to the integer data type? Could someone please explain why my attempt to implement a pointer variable is failing? Thanks all!

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  • How to change mouse pointer icon in Xfce Debian 7 Wheezy?

    - by kadaj
    I copied the cursor theme (oxy-neon or Oxygen Neon) to /usr/share/icons and from Applications Menu - Settings - Mouse, I am able to see the new theme. I clicked on it and the pointer doesn't change. However the text typing icon ('I'), busy icon, hand icon, and resize window icons got changed. The pointer icon remains the same, the black Adwaita. I removed the Adwaita folder from the icons folder, and still the mouse pointer doesn't change. Is the pointer theme specified elsewhere? I have no setting under home directory. I tried logging out, restart, restarting xfwm4, but nothing works. I just found that the icon pointer changes when the pointer is inside Firefox, but it's not consistent. It keeps changing when I click menu items. Very weird. Any idea how to fix this? This is the output of running: gsettings list-recursively org.gnome.desktop.interface : ~$ gsettings list-recursively org.gnome.desktop.interface org.gnome.desktop.interface automatic-mnemonics true org.gnome.desktop.interface buttons-have-icons false org.gnome.desktop.interface can-change-accels false org.gnome.desktop.interface clock-format '24h' org.gnome.desktop.interface clock-show-date false org.gnome.desktop.interface clock-show-seconds false org.gnome.desktop.interface cursor-blink true org.gnome.desktop.interface cursor-blink-time 1200 org.gnome.desktop.interface cursor-blink-timeout 10 org.gnome.desktop.interface cursor-size 24 org.gnome.desktop.interface cursor-theme 'Adwaita' org.gnome.desktop.interface document-font-name 'Sans 11' org.gnome.desktop.interface enable-animations true org.gnome.desktop.interface font-name 'Cantarell 11' org.gnome.desktop.interface gtk-color-palette 'black:white:gray50:red:purple:blue:light blue:green:yellow:orange:lavender:brown:goldenrod4:dodger blue:pink:light green:gray10:gray30:gray75:gray90' org.gnome.desktop.interface gtk-color-scheme '' org.gnome.desktop.interface gtk-im-module '' org.gnome.desktop.interface gtk-im-preedit-style 'callback' org.gnome.desktop.interface gtk-im-status-style 'callback' org.gnome.desktop.interface gtk-key-theme 'Default' org.gnome.desktop.interface gtk-theme 'Adwaita' org.gnome.desktop.interface gtk-timeout-initial 200 org.gnome.desktop.interface gtk-timeout-repeat 20 org.gnome.desktop.interface icon-theme 'gnome' org.gnome.desktop.interface menubar-accel 'F10' org.gnome.desktop.interface menubar-detachable false org.gnome.desktop.interface menus-have-icons false org.gnome.desktop.interface menus-have-tearoff false org.gnome.desktop.interface monospace-font-name 'Monospace 11' org.gnome.desktop.interface show-input-method-menu true org.gnome.desktop.interface show-unicode-menu true org.gnome.desktop.interface text-scaling-factor 1.0 org.gnome.desktop.interface toolbar-detachable false org.gnome.desktop.interface toolbar-icons-size 'large' org.gnome.desktop.interface toolbar-style 'both-horiz' org.gnome.desktop.interface toolkit-accessibility false ~$

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  • Android - Dealing with a Dialog on Screen Orientation change

    - by Donal Rafferty
    I am overriding the onCreateDialog and onPrepareDialog methods or the Dialog class. I have followed the example from Reto Meier's Professional Android Application Development book, Chapter 5 to pull some XML data and then use a dialog to display the info. I have basically followed it exactly but changed the variables to suit my own XML schema as follows: @Override public Dialog onCreateDialog(int id) { switch(id) { case (SETTINGS_DIALOG) : LayoutInflater li = LayoutInflater.from(this); View settingsDetailsView = li.inflate(R.layout.details, null); AlertDialog.Builder settingsDialog = new AlertDialog.Builder(this); settingsDialog.setTitle("Provisioned Settings"); settingsDialog.setView(settingsDetailsView); return settingsDialog.create(); } return null; } @Override public void onPrepareDialog(int id, Dialog dialog) { switch(id) { case (SETTINGS_DIALOG) : String afpunText = " "; if(setting.getAddForPublicUserNames() == 1){ afpunText = "Yes"; } else{ afpunText = "No"; } String Text = "Login Settings: " + "\n" + "Password: " + setting.getPassword() + "\n" + "Server: " + setting.getServerAddress() + "\n"; AlertDialog settingsDialog = (AlertDialog)dialog; settingsDialog.setTitle(setting.getUserName()); tv = (TextView)settingsDialog.findViewById(R.id.detailsTextView); if (tv != null) tv.setText(Text); break; } } It works fine until I try changing the screen orientation, When I do this onPrepareDialog gets call but I get null pointer exceptions on all my variables. The error still occurs even when I tell my activity to ignore screen orientation in the manifest. So I presume something has been left out of the example in the book do I need to override another method to save my variables in or something?

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  • how is data stored at bit level according to "Endianness" ?

    - by bakra
    I read about Endianness and understood squat... so I wrote this main() { int k = 0xA5B9BF9F; BYTE *b = (BYTE*)&k; //value at *b is 9f b++; //value at *b is BF b++; //value at *b is B9 b++; //value at *b is A5 } k was equal to "A5 B9 BF 9F" and (byte)pointer "walk" o/p was "9F BF b9 A5" so I get it bytes are stored backwards...ok. ~ so now I thought how is it stored at BIT level... I means is "9f"(1001 1111) stored as "f9"(1111 1001)? so I wrote this int _tmain(int argc, _TCHAR* argv[]) { int k = 0xA5B9BF9F; void *ptr = &k; bool temp= TRUE; cout<<"ready or not here I come \n"< for(int i=0;i<32;i++) { temp = *( (bool*)ptr + i ); if( temp ) cout<<"1 "; if( !temp) cout<<"0 "; if(i==7||i==15||i==23) cout<<" - "; } } I get some random output even for nos. like "32" I dont get anything sensible. why ?

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  • Fatal error when using FILE* in Windows from DLL

    - by AlannY
    Hi there. Recently, I found a problem with Visual C++ 2008 compiler, but using minor hack avoid it. Currently, I cannot use the same hack, but problem exists as in 2008 as in 2010 (Express). So, I've prepared for you 2 simple C file: one for DLL, one for program: DLL (file-dll.c): #include <stdio.h> __declspec(dllexport) void print_to_stream (FILE *stream) { fprintf (stream, "OK!\n"); } And for program, which links this DLL via file-dll.lib: Program: #include <stdio.h> __declspec(dllimport) void print_to_stream (FILE *stream); int main (void) { print_to_stream (stdout); return 0; } To compile and link DLL: cl /LD file-dll.c To compile and link program: cl file-test.c file-dll.lib When invoking file-test.exe, I got the fatal error (similar to segmentation fault in UNIX). As I said early, I had that the same problem before: about transferring FILE* pointer to DLL. I thought, that it may be because of compiler mismatch, but now I'm using one compiler for everything and it's not the problem. ;-( What can I do now? UPD: I've found solution: cl /LD /MD file-dll.c cl /MD file-test.c file-dll.lib The key is to link to dynamic library, but (I did not know it) by default it links staticaly and (hencefore) error occurs (I see why). P.S. Thanks for patience.

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  • Cross-reference js-object variables when creating object

    - by Ivar Bonsaksen
    Summary: I want to know if it is possible to do something like this: {a: 'A',b: this.a} ...by using some other pointer like {a: 'A',b: self.a} or {a: 'A',b: own.a} or anything else... Full question: I'm trying to extend MyBaseModule using Ext.extend, and need to cross-reference values in the extension object passed to Ext.extend(). Since I'm not yet in context of MyModule, I'm not able to use this to reference the object (See example below line 12). Is there any other way to reference values like this without creating the object first? 1 MyModule = Ext.extend(MyBaseModule, { 2 dataStores: { 3 myDataStore: new Ext.data.Store({...}) 4 }, 5 6 myGridDefinition: { 7 id: 'myGridDefinitionPanel', 8 bodyBorder: false, 9 items: [{ 10 xtype: 'grid', 11 id: 'myGridDefinitionGrid', 12 store: this.dataStores.myDataStore 13 }] 14 } 15 }); Or is the following the only solution? I would like to avoid this if possible, as I find it less readable for large extension definitions. 1 var extensionObject = { 2 dataStores: { 3 myDataStore: new Ext.data.Store({...}) 4 }, 5 6 myGridDefinition: { 7 id: 'myGridDefinitionPanel', 8 bodyBorder: false, 9 items: [{ 10 xtype: 'grid', 11 id: 'myGridDefinitionGrid' 12 }] 13 } 14 }; 15 16 extensionObject.locationsGrid.items[0].store = extensionObject.dataStores.locations; 17 18 MyModule = Ext.extend(MyBaseModule, extensionObject);

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  • Why is my code slower using #import "progid:typelib" than using "MFC Class From TypeLib"?

    - by Pakman
    I am writing an automation client in Visual C++ with MFC. If I right-click on my solution » Add » Class, I have the option to select MFC Class From TypeLib. Selecting this option generates source/header files for all interfaces. This allows me to write code such as: #include "CApplication.h" #include "CDocument.h" // ... connect to automation server ... CApplication *myApp = new CApplication(pDisp); CDocument myDoc = myApp->get_ActiveDocument(); Using this method, my benchmarking function that makes about 12000 automation calls takes 1 second. Meanwhile, the following code: #import "progid:Library.Application" Library::IApplicationPtr myApp; // ... connect to automation server ... Library::IDocumentPtr myDoc = myApp->GetActiveDocument(); takes about 2.4 seconds for the same benchmark. I assume the smart-pointer implementation is slowing me down, but I don't know why. Even worse, I'm not sure how to use #import construct to achieve the speeds that the first method yields. Is this possible? How or why not? Thanks for your time!

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  • How can I declare and initialize an array of pointers to a structure in C?

    - by worlds-apart89
    I have a small assignment in C. I am trying to create an array of pointers to a structure. My question is how can I initialize each pointer to NULL? Also, after I allocate memory for a member of the array, I can not assign values to the structure to which the array element points. #include <stdio.h> #include <stdlib.h> typedef struct list_node list_node_t; struct list_node { char *key; int value; list_node_t *next; }; int main() { list_node_t *ptr = (list_node_t*) malloc(sizeof(list_node_t)); ptr->key = "Hello There"; ptr->value = 1; ptr->next = NULL; // Above works fine // Below is erroneous list_node_t **array[10] = {NULL}; *array[0] = (list_node_t*) malloc(sizeof(list_node_t)); array[0]->key = "Hello world!"; //request for member ‘key’ in something not a structure or union array[0]->value = 22; //request for member ‘value’ in something not a structure or union array[0]->next = NULL; //request for member ‘next’ in something not a structure or union // Do something with the data at hand // Deallocate memory using function free return 0; }

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  • Search string in file (C)

    - by chutsu
    So my code isn't working... test.c:27: warning: passing argument 1 of ‘search’ from incompatible pointer type which is the fgets line. My code opens a file, reads the file line by line, and I'm trying to create a "search" function that will return a value that indicates whether that string is found on that line of the file. My ultimate goal is to achieve a search and replace program. But one step at a time eh? this is what I have so far: #include <stdio.h> #include <string.h> int search(const char *content[], const char *search_term) { int t; for(t=0; content[t]; ++t){ if(!strcmp(content[t], search_term)){ return t; // found } } return 0; // not found } int main(int argc, char *argv[]) { FILE *file; char line[BUFSIZ]; int linenumber=0; char term[20] = "hello world"; file = fopen(argv[1], "r"); if(file != NULL){ while(fgets(line, sizeof(line), file)){ if(search(line, term) != -1){ printf("Search Term Found!!\n"); } ++linenumber; } } else{ perror(argv[1]); } fclose(file); return 0; }

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  • How to determine 2D unsigned short pointers array length in c++

    - by tuman
    Hello, I am finding it difficult to determine the length of the columns in a 2D unsigned short pointer array. I have done memory allocation correctly as far as I know. and can print them correctly. plz see the following code segment: int number_of_array_index_required_for_pointer_abc=3; char A[3][16]; strcpy(A[0],"Hello"); strcpy(A[1],"World"); strcpy(A[2],"Tumanicko"); cout<<number_of_array_index_required_for_pointer_abc*sizeof(unsigned short)<<endl; unsigned short ** pqr=(unsigned short **)malloc(number_of_array_index_required_for_pointer_abc*sizeof(unsigned short)); for(int i=0;i<number_of_array_index_required_for_pointer_abc;i++) { int ajira = strlen(A[i])*sizeof(unsigned short); cout<<i<<" = "<<ajira<<endl; pqr[i]=(unsigned short *)malloc(ajira); cout<<"alocated pqr[i]= "<<sizeof pqr<<endl; int j=0; for(j=0;j<strlen(A[i]);j++) { pqr[i][j]=(unsigned short)A[i][j]; } pqr[i][j]='\0'; } for(int i=0;i<number_of_array_index_required_for_pointer_abc;i++) { //ln= (sizeof pqr[i])/(sizeof pqr[0]); //cout<<"Size of pqr["<<i<<"]= "<<ln<<endl; // I want to know the size of the columns i.e. pqr[i]'s length instead of finding '\0' for(int k=0;(char)pqr[i][k]!='\0';k++) cout<<(char)pqr[i][k]; cout<<endl; }

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  • Setting Cursor property has no effect (C#)

    - by Knarf Navillus
    Hello, I have a class that I've derived from System.Windows.Forms.Panel, and my application has a main form with one of these panels. On the whole, the panel works great! The only thing I'm having trouble with is setting the cursor. Whether I'm setting it to one of the static members of the Cursors class (Default, WaitCursor, etc.) or setting it to a custom cursor that I've loaded from a resource, the end result is the same: it does nothing. I still see the default mouse pointer, no matter what. This line of code is inside a method of my panel-derived class: this.Cursor = Cursors.WaitCursor; I can set a break point there, and see that this line is being hit when I expect it to. I've also created an override for the OnCursorChanged method, and set a breakpoint in there just to see if it's being triggered. I can verify that both breakpoints are being hit when I expect them to. However, the cursor just never changes. There must be something that I'm missing. Does anyone have any ideas? P.S. I also did try setting Current.Cursor as well, however that did not help.

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  • Confusion about pointers and their memory addresses

    - by TimothyTech
    alright, im looking at a code here and the idea is difficult to understand. #include <iostream> using namespace std; class Point { public : int X,Y; Point() : X(0), Y(0) {} }; void MoveUp (Point * p) { p -> Y += 5; } int main() { Point point MoveUp(&point) cout <<point.X << point.Y; return 0; } Alright, so i believe that a class is created and X and Y are declared and they are put inside a constructor a method is created and the argument is Point * p, which means that we are going to stick the constructor's pointer inside the function; now we create an object called point then call our method and put the pointers address inside it? isnt the pointers address just a memory number like 0x255255? and why wasnt p ever declared? (int * p = Y) what is a memory addres exactly? that it can be used as an argument?

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