Delete is an operator that is used to destroy array and non-array (pointer) objects which are created by new expression. You pointed it at NULL, leaving behind leaked memory (the new int you allocated).You should free the memory you were pointing at. (C++11, 3.7.3). Step 5 Allocate the memory dynamically at runtime. C++ after delete pointer int* ptr = new int(6); reserves some memory where ptr will be pointing to, that memory will be good to store one int , 6 or any other, it cannot be used to do anything else, you can reliably store the data there and access it later. A-143, 9th Floor, Sovereign Corporate Tower, We use cookies to ensure you have the best browsing experience on our website. Understand that English isn't everyone's first language so be lenient of bad It may be initialized to zero the first time, but you can't rely on that behavior. Void pointer is a pointer which is not associate with any data types. Or consider using calloc, which zeros out the memory before returning the pointer to you. A null pointer indicates that there is "nothing there" - it points at nothing. The rubber protection cover does not pass through the hole in the rim. Is there a verb meaning depthify (getting more depth)? - there is "what is pointed" by the pointer (the memory) True. The error says the memory wasn't allocated but 'cout' returned an address. It can be used using a Delete operator or Delete [] operator. 2022 ITCodar.com. (I literally) learn something, @AmelSalibasic The memory associated with the variable on the stack will be freed only once it goes out of scope. Not the answer you're looking for? Deleting NULL pointer : Deleting a NULL does not cause any change and no error. Trying to delete pointer to a local stack allocated variable. That's the kind of thinking that creates very buggy C or C++ programs. Deleting a pointer does not destruct a pointer actually, just the memory occupied is given back to the OS. Chances are they have and don't get it. How many transistors at minimum do you need to build a general-purpose computer? Can't call delete on it. How could my characters be tricked into thinking they are on Mars? The pointer returned by new should belong to a resource handle (that can call delete ). Is it cheating if the proctor gives a student the answer key by mistake and the student doesn't report it? Connect and share knowledge within a single location that is structured and easy to search. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. C++11 comes with several. If you meant deallocate a pointer, then the command is a keyword. Your question reveals that you think that freeing up memory is as simple as releasing it when you're done with it. The above did nothing at all. To learn more, see our tips on writing great answers. Is there any reason on passenger airliners not to have a physical lock between throttles? You didn't free anything, as the pointer pointed at NULL. Differences in delete and free are: Instead of changing where q points, though, you can copy the value you want into the space that q points to: Here you're changing the value stored in the location to which q points, but you're not changing q itself. Declaring Pointer to Pointer is similar to declaring a pointer in C. The difference is we have to place an additional '*' before the name of the pointer. If you're just going to copy a string into it, you don't need to initialize it to zero first; you can just copy the string and (if necessary) append a '\0' to the end. Only. The behaviour of your program is undefined. Does balls to the wall mean full speed ahead or full speed ahead and nosedive? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. 2. Regardless, no clarification is necessary here, it's obvious why OP is observing this behavior. User has privilege to deallocate the created pointer variable by this delete operator. This Hmm okay, I'm not sure what smart pointers are, but I'll look into it, thanks! Use smart pointers instead which can handle these things for you with little overhead. Let's consider a program to delete NULL pointer using the delete operator in C++ programming language. The more correct term is "with automatic storage duration". The delete operator is used to deallocate the memory. For deleteing the pointer you need to use . New operator is used for dynamic memory allocation which puts variables on heap memory. Did the apostolic or early church fathers acknowledge Papal infallibility? The first variable was allocated on the stack. Is using ::New() allocating my smart pointer on the heap or the stack? Your program attempts to free this memory using delete, which is undefined behavior since you're calling delete for memory that wasn't allocated using new. How many transistors at minimum do you need to build a general-purpose computer? 2 Answers Sorted by: 3 You are already deallocating what you have allocated but doublePtrNode [i]->value=i; assumes that you've allocated a Node there, but you haven't so the program has undefined behavior. Making statements based on opinion; back them up with references or personal experience. delete this; You can only use delete on a pointer to memory that you have allocated using new. Step 6 Enter an element that to be deleted. Even if you had allocated memory in. In general programs only use memset or calloc if they really need the memory buffer to be initialized to zero. But this is how it is done: // Allocate a new myClass instance and let x point at that instance myClass* x = new myClass(); // Replace the data pointed at by x to be a new myClass instance *x = myClass(); // At this point, x points at the same piece of memory // but the data stored at that memory is different. If the pointer returned by new is assigned to a plain/naked pointer, the object can be leaked. Provide an answer or move on to the next question. In a nutshell, they do what I described. They are removed from memory at the end of a functions execution and/or the end of the program. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Step 3 Input the array elements. You could replace your data with something like 0s or 0xFFs with memset(), which would overwrite your data. And it's logic that it prints 0 because you did: Thanks for contributing an answer to Stack Overflow! your object that was deleted, it might still work. You must do so /before/ free()ing it. Why is the federal judiciary of the United States divided into circuits? Why does pointer not update on empty BST tree in C when inserting node? How is the merkle root verified if the mempools may be different? 20 Bay Street, 11th Floor Toronto, Ontario, Canada M5J 2N8 By writing: myPointer = The address of where the data in myVar is stored. Context: I'm trying to wrap my head around pointers, we just saw them a couple of weeks ago in school and while practicing today I ran into a silly? Delete is an operator that is used to destroy array and non-array(pointer) objects which are created by new expression. What are the differences between a pointer variable and a reference variable? You can call memset to clear the memory returned from malloc. What does "dereferencing" a pointer mean? How can I delete the data to which a pointer points to ? Deleting a pointer in C++ 1 & 2 myVar = 8; //not dynamically allocated. It will be deallocated as soon as it goes out of scope. @DarkCthulhu Thanks! Strictly speaking, the C programming language has no delete (it is a C++ keyword), it just provides the free [ ^] function. A void pointer is a pointer that has no associated data type with it. As we saw in the article about removing elements from a sequence container, to remove elements in a vector based on a predicate, C++ uses the erase-remove idiom: vector<int> vec {2, 3, 5, 2}; vec.erase (std::remove_if (vec.begin (), vec.end (), [] (int i) { return i % 2 == 0;}), vec.end ()); Which we can wrap in a more expressive function call: 1) delete operator works only for objects allocated using operator new (See this post ). If you're using C++, do not use raw pointers. Ah, I see. If you're just going to copy a string into it, you don't need to initialize it to zero first; you can just copy the string and (if necessary) append a '\0' to the end. Though that might be considered extraneous and could get optimized out by your compiler. Use smart pointers instead which can handle these things for you with little overhead. @tadman . You can access it untill the memory is used for another variable, or otherwise manipulated. To do this: There is a rule in C++, for every new there is a delete. Is the EU Border Guard Agency able to tell Russian passports issued in Ukraine or Georgia from the legitimate ones? Here, Below are examples where we can apply delete operator:1. I don't understand why you're accusing me of posting a "glib" answer when your own answer, posted before mine, was "put new data there." On the second example the error is not being triggered but doing a cout of the value of myPointer. There is no way to access that allocated new int anymore, hence memory leak. q still points to the block you got from new, so it's safe to delete it. I rarely, if ever, reassign individual heap allocated objects. It will probably start as garbage until you put your data there, and your data will stay there until you put something else there. rev2022.12.9.43105. various way to delete pointer to pointer morz i just search for a while in c++ groups but cannot find good answer. Where does the idea of selling dragon parts come from? Syntax : delete <variable name> or delete [ ] <array_name>. The content must be between 30 and 50000 characters. When you have a pointer pointing to some memory there are three different things you must understand: With arrays, why is it the case that a[5] == 5[a]? Asking for help, clarification, or responding to other answers. Which means Delete operator deallocates memory from heap. CPP. Because first you create the pointer and assign its value to myPointer, second you delete it, third you print it. It destroys the memory block or the value pointed by the pointer. With rare exceptions, C++ programmers should not have to write new or delete ever again. It's simple, really - for every new, there should be a corresponding delete. If you're using C++, do not use raw pointers. You can call delete only on memory you allocated dynamically (on the heap) using the new operator. It returns an address that points to a memory location that has been deleted. You can do this explicitly using std::list::iterator, but it's easier to simply use a range-based for-loop: 1 2 3 4 for (Object* obj : objList) { obj->PrintValue (); } Last edited on May 10, 2021 at 5:39am May 10, 2021 at 5:57am seeplus (5744) To learn more, see our tips on writing great answers. i have code like this: int **ptr; ptr = new char * [2]; ptr [0] = new int (5); ptr [1] = new int (16); i know we can delete ptr like this: for (int i = 0; i <2; i++) delete ptr [i]; delete ptr; But can i delete like this? (Opencv and C++), What Does the Standard Say About How Calling Clear on a Vector Changes the Capacity, How to Stop Name-Mangling of My Dll's Exported Function, Who Deletes the Memory Allocated During a "New" Operation Which Has Exception in Constructor, How to Redefine a C++ MACro Then Define It Back, Is Storing an Invalid Pointer Automatically Undefined Behavior, Template Deduction for Function Based on Its Return Type, How to Avoid the Diamond of Death When Using Multiple Inheritance, About Us | Contact Us | Privacy Policy | Free Tutorials. You pointed it at NULL, leaving behind leaked memory (the new int you allocated). I think you're relying on a technicality here. In any case, free on a null pointer does nothing. The code presented here can be refactored in many different ways; I only focus on the smart pointer cases. You can access it untill the memory is used for another variable, or otherwise manipulated. To be even more clear, delete doesn't care about what variable it operates on, it only cares about what that variable points to. Find code solutions to questions for lab practicals and assignments. This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL). Can a prospective pilot be negated their certification because of too big/small hands? Recommended to read this post before moving forward: How to write Smart Pointer for a given class in C++? Thanks for contributing an answer to Stack Overflow! Question: How do I delete a pointer in C++? Step 2 Declare and read the array size at runtime. In addition, check out this lecture on stack frames. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. How did muzzle-loaded rifled artillery solve the problems of the hand-held rifle? Delete doesn't destroy the object. The behavior of a program that adds specializations for remove_pointer is undefined. C++11 comes with several. I've seen quite a few questions over in SO about deleting pointers but they all seem to be related to deleting a class and not a 'simple' pointer (or whatever the proper term might be), here's the code I'm trying to run: Sorry for the long question, wanted to make this as clear as possible, also to reiterate, I have little programming experience, so if someone could answer this using layman's terms, it would be greatly appreciated! Something went wrong. So it is good practice to set a pointer to NULL (0) after deleting. Deleting a NULL pointer does not delete anything. There is no way to access that allocated new int anymore, hence memory leak. Or consider using calloc, which zeros out the memory before returning the pointer to you. C++ Programming Foundation- Self Paced Course, Data Structures & Algorithms- Self Paced Course, Comparison of static keyword in C++ and Java, C++ Program to Show Use of This Keyword in Class, Output of Java Programs | Set 39 (throw keyword), Output of Java Programs | Set 44 (throws keyword). You can call delete only on memory you allocated dynamically (on the heap) using the new operator. Don't attempt to derefererence either b or c after the delete call though, the behaviour on doing that is also undefined. In this case, that happens to be memory that's allocated on the stack when the scope of the main() function is entered, and is freed automatically when the scope of main() exits. The latter is more often referred to as "freeing", while the former is more often called "deleting". +1 (416) 849-8900. Trying to delete Non-pointer object. Deleting pointer with or without value, 5. deleting memory dynamically allocated by malloc. new is never called. It is also called general purpose pointer. Step 4 Declare a pointer variable. Answer: Smart pointer in C++ can be used to delete pointers of object returned by Factory method in C++ in the client code for example in main () method. Can virent/viret mean "green" in an adjectival sense? You are calling new n+1 times, so you should call delete n+1 times, or else you leak memory. Deleting Array Objects: We delete an array using [] brackets. Do you need your, CodeProject, Deleting a pointer (or deleting what it points to, alternatively) means, p was allocated prior to that statement like, It may also refer to using other ways of dynamic memory management, like free, which was previously allocated using malloc or calloc. Answer (1 of 11): Now you understand why pointer bugs are so prevalent. If you had written. The asterisk * used to declare a pointer is the same asterisk used for multiplication. How could my characters be tricked into thinking they are on Mars? You can call delete only on memory you allocated dynamically (on the heap) using the new operator. It is not recommended to use delete with malloc().6. Seems to work to me, the pointer is no longer storing an address, is this the proper way to delete a pointer? The pointer itself is a local variable allocated on the stack. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. All memory on the stack is freed automatically at the end of main(): p, d and x (the variable holding the address, not the address it points to) were all allocated on the stack. Find centralized, trusted content and collaborate around the technologies you use most. If the object is created using new, then we can do delete this, otherwise behavior is undefined. What REALLY happens when you don't free after malloc before program termination? You're a QPP member,aren't you? Not the answer you're looking for? You are trying to delete a variable allocated on the stack. Thank you, I selected your answer for a) explaining what was wrong and b) giving a best practice, thanks much! Which means Delete operator deallocates memory from heap. Assigning it to. You can call memset to clear the memory returned from malloc. You didn't free anything, as the pointer pointed at NULL. @EricPostpischil but if there is old data and I put in a new char at the first position and then iterate until '\0', this will give me not the desired result, since the old data interferes with the new Glib answers before a question has been clarified risk overlooking the real problem. Really? myPointer = new int; delete myPointer; //freed memory myPointer = NULL; //pointed dangling ptr to NULL The better way: If you're using C++, do not use raw pointers. Pointer to object is not destroyed, value or memory block pointed by pointer is destroyed. 1980s short story - disease of self absorption. return 0; } Seeing as how no memory was allocated after that, and you didn't erase. When would I give a checkpoint to my D&D party that they can return to if they die? It may be initialized to zero the first time, but you can't rely on that behavior. Posted 28-Dec-15 0:55am CPallini Solution 2 A null pointer indicates that there is "nothing there" - it points at nothing. In C++, the delete operator should only be used either for the pointers pointing to the memory allocated using new operator or for a NULL pointer, and free () should only be used either for the pointers pointing to the memory allocated using malloc () or for a NULL pointer. class A. deleting indiviual pointers from an array. 3. Although above program runs fine on GCC. rev2022.12.9.43105. 2) Once delete this is done, any member of the deleted object should not be accessed after deletion. : delete ptr; How does the Chameleon's Arcane/Divine focus interact with magic item crafting? If a question is poorly phrased then either ask for clarification, ignore it, or. No. We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. Use smart pointers instead which can handle these things for you with little overhead. Advantages of void pointers: 1) malloc () and calloc () return void * type and this allows these functions to be used to allocate memory of any data type (just because of . delete pearl; pearl->eat (); //Works! "delete this" in C++ If the object is created using new, then we can do delete this, otherwise behavior is undefined. In order to hold something new, you call, "On the stack" is an implementation detail -- one that C++ conspicuously avoids mentioning. Delete is an operator in C++ that can be used to free up the memory blocks that has been allocated using the new operator. How to sort an array of pointers by the addresses of what is inside the pointers. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The reason you don't see the first example is because it's wrong. Ask genuine questions. Useful, because the Stack has a limited size and you might want to mess about with a big load of 'ints' without a stack overflow error. Just use the stack A void pointer can hold address of any type and can be typecasted to any type. In general programs only use memset or calloc if they really need the memory buffer to be initialized to zero. Thanks, THIS was super helpful, I thought I HAD to delete all pointers, didn't know that was only for the ones that were new'd, thanks. All Rights Reserved. What happens when you delete a pointer in C++? You can however use pointers to allocate a 'block' of memory, for example like this: This will allocate memory space for 20000 integers. Designed by Colorlib. Making statements based on opinion; back them up with references or personal experience. C++11 comes with several. Online C Queue programs for computer science and information technology students pursuing BE, BTech, MCA, MTech, MCS, MSc, BCA, BSc. Allow non-GPL plugins in a GPL main program. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Why should I use a pointer rather than the object itself? Did neanderthals need vitamin C from the diet? Smart pointer will handle memory deallocation itself instead of manual call. Does the collective noun "parliament of owls" originate in "parliament of fowls"? - not all pointers need to have their memory deleted: you only need to delete memory that was dynamically allocated (used new operator). Pointers are similar to normal variables in that you don't need to delete them. Whenever you call new, you should then 'delete' at the end of your program, because otherwise you will get a memory leak, and some allocated memory space will never be returned for other programs to use. Signs are OP is not initializing the memory they allocate, meaning their use of their first. New operator is used for dynamic memory allocation which puts variables on heap memory while delete operator deallocates memory from heap. Why Smart pointers can not be declared the usual Pointer way, c++ Deleting multiple head/tail of linked list stored in vector. myPointer = new int; //dynamically allocated, can call delete on it. Motivation FactSetters have gotten a lot of mileage out of boost::shared_ptr over the years. Something can be done or not a fit? That brings up the second point--if the pointer goes out of scope before you deallocate the object you allocated on the heap, you will never be able to deallocate it, and will have a memory leak. 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Your first code snippet does indeed delete the object. Share Follow edited May 23, 2017 at 10:31 Community Bot 1 1 q points to statically allocated memory, not something you got from new, so you can't delete it. Step 1 Declare and read the number of elements. Seems the most straightforward use to use and delete a pointer? Ready to optimize your JavaScript with Rust? Pointers to variables on the stack do not need to be deleted. How to solve null pointer exception in steams, list array? You can't assume that memory returned from malloc is initialized to anything. How to Declare a Pointer to a Pointer in C? We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. Do you need to delete pointers C++? delete will deallocate the memory to which its operand points. Don't tell someone to read the manual. How to delete the data of a pointer in C? So unless you assign another value to myPointer, the deleted address will remain. Deleting pointer to object in unordered_map. The first variable was allocated on the stack. Why does the distance from light to subject affect exposure (inverse square law) while from subject to lens does not? C++ deleting a pointer itself instead of deleting the pointed-to-data, pointer being freed was not allocated for pointer assignment. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. Deleting array elements in JavaScript - delete vs splice. Pointer to object is not destroyed, value or memory block pointed by pointer is destroyed/deallocated. Ready to optimize your JavaScript with Rust? void pointer in C / C++. Deleting variables of User Defined data types: Exceptions:1. The general form of a pointer variable declaration is type *var-name; Here, type is the pointer's base type; it must be a valid C data type and var-name is the name of the pointer variable. spelling and grammar. What are the differences between a pointer variable and a reference variable? Why is this usage of "I've to work" so awkward? char *p = (char *) malloc (10 * sizeof (char)); . Delete can be used by either using Delete operator or Delete [ ] operator New operator is used for dynamic memory allocation which puts variables on heap memory. You are not allocating a 2D array - you are making n+1 separate allocations, completely unrelated to each other as far as the compiler can tell. So it is good practice to set a pointer to NULL (0) after deleting. Since freeing p doesn't delete the data stored at the particular memory address I'm facing the problem that for large pointers the newly allocated memory overlaps with the old one what is obviously problematic. You probably missed something hereCan you delete nothing? let p point to some chars free (p); char *p = (char *) malloc (10 * sizeof (char)); Since freeing p doesn't delete the data stored at the particular memory address I'm facing the problem that for large pointers the newly allocated memory overlaps with the old one what is obviously problematic. 2. Solution 1 You cannot 'delete' a null pointer. Does #3 really work? Find centralized, trusted content and collaborate around the technologies you use most. Syntax: data_type_of_pointer **name_of_variable = & normal_pointer_variable; Example: Why does the USA not have a constitutional court? Deleting a pointer does not destruct a pointer actually, just the memory occupied is given back to the OS. It is not safe to delete a void pointer in C/C++ because delete needs to call the destructor of whatever object it's destroying, and it is . Effect of coal and natural gas burning on particulate matter pollution. issue, it can be super straightforward to you but I have little to none programming experience. 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Received a 'behavior reminder' from manager. free (and malloc, calloc etc) is used for basic types, but in C++ new and delete can be used for them likewise, so there isn't much reason to use malloc in C++, except for compatibility reasons. I believe you're not fully understanding how pointers work. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Step 7 After deletion, the elements are shifted to left by one position. Maybe that pointe. What is the difference between const int*, const int * const, and int const *? delete operator Since it is the programmer's responsibility to deallocate dynamically allocated memory, programmers are provided delete operator in C++ language. {. public: void fun () {. So you can't delete or free it, because you didn't assign it. email is in use. You can not do this. C Program to perform insert & delete operations on queue using pointer. So the address that cout prints is the address of the memory location of myVar, or the value assigned to myPointer in this case. You should free the memory you were pointing at. What is a smart pointer and when should I use one? C++ C++,c++,pointers,delete-operator,forward-list,C++,Pointers,Delete Operator,Forward List, f_ std:: remove_pointer. But it does not set memory before free as requested by OP. the pointer, it was simply still a valid object. What is the difference between #include and #include "filename"? Appropriate translation of "puer territus pedes nudos aspicit"? delete pointer; does not delete the pointer itself, but the data that the pointer is pointing to. What is a smart pointer and when should I use one? Why should I use a pointer rather than the object itself? You must delete the same block of memory that you obtained from new. NULL equals 0, you delete 0, so you delete nothing. By using our site, you You can't assume that memory returned from malloc is initialized to anything. In the last line above, r points to the block that was originally pointed to by q and allocated by new, so you can safely delete it. How do I set, clear, and toggle a single bit? The above did nothing at all. Here is the syntax of delete operator in C++ language, delete pointer_variable; Here is the syntax to delete the block of allocated memory, delete [ ] pointer_variable; is dynamically creating a pointer, and then changing a pointer address to something else still deleting the original allocated space? Not sure if it was just me or something she sent to the whole team. C++ allows that you try to delete a pointer that points to null but it doesn't actually do anything, just doesn't give any error. It points to some data location in storage means points to the address of variables. Asking for help, clarification, or responding to other answers. If you see the "cross", you're on the right track, What is this fallacy: Perfection is impossible, therefore imperfection should be overlooked, QGIS expression not working in categorized symbology. 1. Not stuff that can be found one StackOverflow or even *gasp* Google lol - But here's your troll answer :-P If you meant deallocate a pointer. What was your intent in making that statement, if not to answer the OP's question? It has no effect on the pointer pointing to the starting address of that memory location. Why won't the first case work? There's no such concept as "deleting" data in C. When you allocate some memory for data, there will always be data there. I want to just add that the allocated memory WILL be returned for other programs to use, but only AFTER your program has finished executing. In your case, you should simply remove the delete. Examples: delete is used for classes with a destructor since delete will call the destructor in addition to freeing the memory. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. Does integrating PDOS give total charge of a system? - this memory address Provides the member typedef type which is the type pointed to by T, or, if T is not a pointer, then type is the same as T . Answer (1 of 7): Try [code ]delete **p;[/code] Other posters are correct to suggest that naked delete is a code smell, that using a smart pointer and RAII is better than using naked pointers, and that an object-oriented approach where the pointer is a class member and deleted in the destructor i. Program3.cpp #include <iostream> using namespace std; int main () { // initialize the integer pointer as NULL int *ptr = NULL; // delete the ptr variable delete ptr; cout << " The NULL pointer is deleted."; return 0; } Output Syntax: // Release memory pointed by pointer-variable delete pointer-variable; Here, the pointer variable is the pointer that points to the data object created by new. If you are going to use raw owning pointers, you could fix it like this: Connect and share knowledge within a single location that is structured and easy to search. Obtain closed paths using Tikz random decoration on circles. then you could write either delete b; or delete c; to free your memory. 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