A pointer is a data type whose value refers directly to (or "points to") another value stored elsewhere in the computer memory using its address.

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109
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26answers
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Are null references really a bad thing?

I've heard it said that the inclusion of null references in programming languages is the "billion dollar mistake". But why? Sure, they can cause NullReferenceExceptions, but so what? Any element of ...
76
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4answers
44k views

How is a Java reference different from a C pointer?

C has pointers and Java has what is called references. They have some things in common in the sense that they all point to something. I know that pointers in C store the addresses they point to. Do ...
66
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32answers
17k views

What's a nice explanation for pointers? [closed]

In your own studies (on your own, or for a class) did you have an "ah ha" moment when you finally, really understood pointers? Do you have an explanation you use for beginner programmers that seems ...
55
votes
17answers
7k views

What programming problems are best solved by using pointers? [closed]

Well, I basically understand how to use pointers, but not how best to use them in order to do better programming. What are good projects or problems to resolve involving the use of pointers so I can ...
31
votes
10answers
17k views

Why are pointers not recommended when coding with C++?

I read from somewhere that when using C++ it is recommended not to use pointers. Why is pointers such a bad idea when you are using C++. For C programmers that are used to using pointers, what is the ...
27
votes
10answers
8k views

What is the “type” of data that pointers hold in the C language?

I know that pointers hold addresses. I know that pointers' types are "generally" known based on the "type" of data they point to. But, pointers are still variables and the addresses they hold must ...
25
votes
10answers
5k views

Isn't the use of pointer variables a memory overhead?

In languages like C and C++, while using pointers to variables we need one more memory location to store that address. So isn't this a memory overhead? How is this compensated? Are pointers used in ...
24
votes
12answers
21k views

int* i; or int *i; or int * i; [closed]

What is your favorite method to declare a pointer? int* i; or int *i; or int * i; or int*i; Please explain why. see also: http://www.stroustrup.com/bs_faq2.html#whitespace
24
votes
4answers
4k views

Why do C++ and Java both use the notion of “reference” but not in the same sense?

In C++ a reference argument to a function allows the function to make the reference refer to something else: int replacement = 23; void changeNumberReference(int& reference) { reference = ...
22
votes
12answers
7k views

Why does void in C mean not void?

In strongly-typed languages like Java and C#, void (or Void) as a return type for a method seem to mean: This method doesn't return anything. Nothing. No return. You will not receive anything from ...
22
votes
4answers
4k views

Is a memory of all possible permutations of a kilobyte block and pointers possible?

This is a hard enough idea to wrap my head around and I would greatly appreciate any edits/help to get it more readable for those in-the-know. Is it theoretically possible to have a hard drive that ...
21
votes
3answers
7k views

Why Increment Pointers?

I just recently started learning C++, and as most people (according to what I have been reading) I'm struggling with pointers. Not in the traditional sense, I understand what they are, and why they ...
21
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15answers
5k views

Will real world applications ever need a 128-bit flat address space?

This is a bit "one megabyte should be enough for anyone", but... A 64-bit flat address space allows up to 4.3ish billion times more space than a 32-bit address space. That's 17,179,869,184 GiB. ...
19
votes
4answers
16k views

Any real use of pointers in C#? [closed]

What is a situation while coding in C# where using pointers is a good or necessary option? I'm talking about unsafe pointers.
18
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10answers
9k views

What is so difficult about pointers/recursion? [closed]

In the perils of java schools Joel discusses his experience at Penn and the difficulty of "segmentation faults". He says [segfaults are difficult until you] "take a deep breath and really try ...
17
votes
4answers
15k views

In C++ why and how are virtual functions slower?

Can anyone explain in detail, how exactly the virtual table works and what pointers are associated when virtual functions are called. If they are actually slower, can you show the time that the ...
13
votes
5answers
2k views

How is precedence determined in C pointers?

I've come across two pointer declarations that I'm having trouble understanding. My understanding of precedence rules goes something like this: Operator Precedence ...
11
votes
4answers
2k views

Pointer indexing

I am currently reading a book titled "Numerical Recipes in C". In this book, the author details how certain algorithms inherently work better if we had indices starting with 1 (I don't entirely follow ...
11
votes
5answers
2k views

Who invented pointers?

Pretty simple question, but something I haven't been able to find out. Who was the first person to describe the idea of a pointer? The abstract concept itself?
11
votes
4answers
1k views

If you favor “T *var”, do you ever write “T*”? [duplicate]

Possible Duplicate: int* i; or int *i; or int * i; Thinking about where we place our asterisks; how do those that prefer to keep the "pointerness" away from the type and with the identifier ...
8
votes
8answers
23k views

What are use cases and advantages of pointers? [closed]

I often struggle to see the advantages of pointers (except for low level programming). Why use of char* instead of a String or char[] or what advantages pointer arithmetic brings. So what are the ...
8
votes
4answers
349 views

You've shipped, you get a rare seg fault. Pointer checking or let it go?

You've shipped, asserts are turned off, you receive a rare crash report indicating that a null pointer violation occurred in your code. In a development environment, the problem would have been ...
7
votes
5answers
2k views

When and why would we use immutable pointers?

In Java, the String object is both immutable and also a pointer (aka reference type). I'm sure there are other types/objects which are both immutable and a pointer as well and that this extends ...
7
votes
5answers
16k views

Is there any difference between pointers and references? [duplicate]

References and pointers do the same thing as I know. Is there any difference between them? If there is no difference, why we call them reference not pointer?
7
votes
5answers
3k views

What is the purpose of arrays in C, when pointers could have done the job?

Arrays and pointers are not the same thing in C, although they are related and can be used similarly. So far we all agree. However, I don't see why arrays were included in C, when pointers could have ...
7
votes
1answer
4k views

Is this a valid example of a dangling pointer?

The book "Data Structures in C" (Horowitz and Sahni) suggests that in the following code the pointer pf is behaving as a dangling reference: float f,*pf; pf=(float*) malloc(sizeof(float)); *pf=2.6; ...
7
votes
1answer
5k views

raw, weak_ptr, unique_ptr, shared_ptr etc… how to choose them wisely

There is a lot of pointers in C++ but to be honest in 5 years or so in c++ programmation (specifically with the Qt Framework) I only use the old raw pointer : SomeKindOfObject *someKindOfObject = ...
7
votes
2answers
269 views

Autoreleasing objects in Reference Counting Systems

I'm experimenting a bit in C and I'm trying to implement my own Reference Counting System. I've mainly worked with Objective-C in the past but AFAIK autoreleasing objects is something that is unique ...
7
votes
1answer
494 views

Key / Value store development porting to modern C++

I am developing a database server similar to Cassandra. Development were started in C, but things became very complicated without classes. Currently I ported everything in C++11, but I am still ...
6
votes
4answers
3k views

Do I need to understand pointers to use C++?

Well, I love C++, I have been using it for a while: I like all the libraries (Allegro, SDL, QT, Ogre, etc.), but I have a problem: I don't understand pointers. Do I really need them ? I just program ...
6
votes
4answers
682 views

What's a good way to explain the need for pointing to a pointer?

Understanding what a pointer (an address) is, is fairly easy and an eleven-year old can understand it. But how do we express why we have a need for a pointer to a pointer? what is a very pedagogical ...
6
votes
6answers
1k views

why are both index[array] and array[index] valid in C?

For example consider: int index = 3; int array[4] = {0, 1, 2, 3}; then both index[array] and array[index] are valid expressions, much like *(index + array) and *(array + index). In C arrays why is ...
6
votes
4answers
7k views

What is the difference between a pointer pointing to 0x0 location and a pointer set to NULL?

Is a pointer pointing to 0x0000 the same as a pointer set to NULL? If NULL value is defined in the C language, then what location does it physically translate to? Is it the same as 0x0000. Where can I ...
6
votes
2answers
731 views

Is it better to use an external variable or to pass around a pointer?

While writing in C, I have always wondered about when is the best time to use an external variable. I generally prefer to pass a pointer into a method. Is there a correct time to use an external ...
6
votes
1answer
258 views

Hardware that accelerates pointer dereferencing?

Most modern languages make a heavy use of pointers / references: a typical OOP language uses VMT lookups, a typical functional language builds key data structures out of pointers, etc. Even typical C ...
6
votes
1answer
911 views

What are the real life use cases for tagged pointers? [closed]

What are the real life use cases for tagged pointers? This is mostly coming from reading about small 64-bit systems and possible uses of 64-bit word pointers. To my understanding tagged pointers are ...
5
votes
5answers
2k views

What's so bad about pointers in C++?

To continue the discussion in Why are pointers not recommended when coding with C++ Suppose you have a class that encapsulates objects which need some initialisation to be valid - like a network ...
5
votes
3answers
1k views

Is it a common practice among professional programmers to avoid the use of raw pointers? [duplicate]

C++ tools and libraries have become more powerful than ever. For instance, we can replace arrays by vectors. We can replace pointers by references. We can use smart-pointers. Is it a common practice ...
5
votes
0answers
2k views

Why would someone use this type of cast in c? The reference of a float is cast to int pointer and then dereferenced [migrated]

I was reading about Carmack's fast inverse square root algorithm, and noticed this: float x; // ... // int i = *(int*)&x; Why would someone choose to use this weird type of casting instead of ...
4
votes
6answers
2k views

Is it best to minimize using pointers in C?

I think most people would agree that pointers are a major source of bugs in C programs (if not the greatest source of bugs). Other languages drop pointers entirely for this reason. When working in C, ...
4
votes
4answers
2k views

Was C designed to facilitate Object-Oriented programming?

I am trying to broaden my understanding of the history and development of object-oriented programming, and I am curious to find out if C was designed to facilitate Object-Oriented programming? (like ...
4
votes
2answers
2k views

Smart Pointers inside class vs Normal Pointers with Destructor

Regarding pointers which are members of classes. Should they be of a smart pointer type or is it enough to simply deal with them in the destructor of the class they are contained in?
4
votes
3answers
257 views

adding array pointer in c

I am having problems understanding how this equation works in c: char *sum(char *a, int b) { return &a[b]; } printf("%d", sum(5, 4)); I understand how arrays work, and I understand how to ...
4
votes
3answers
286 views

C++ returning persistent objects

I'm currently trying to learn best practices in C++ after coming from a C# background. I understand that there are three ways of handling objects: By value (objects are copied or moved when passed ...
4
votes
1answer
599 views

The right way to remove an item from a linked list

In this Slashdot interview Linus Torvalds is quoted as saying: I've seen too many people who delete a singly-linked list entry by keeping track of the "prev" entry, and then to delete the entry, ...
3
votes
2answers
322 views

What happens when using address before it's allocated?

The very simple piece of C++ code below is incorrect, it's easy to see why and tools like Valgrind will tell you. In running several C++ codes containing this kind of error, I noticed that each time, ...
3
votes
6answers
1k views

What are memory addresses? [closed]

I have more or less 0 knowledge in low-level topics, so forgive my possible ignorance. I know that in languages such as C, pointers hold 'memory addresses', i.e. strings (or binary data?) written in ...
3
votes
5answers
2k views

function pointers are so complex to me

I found this code sample in this answer by Armen Tsirunyan. class MyClass { public: typedef void (*funcPtr)(int, int); MyClass(funcPtr whatToCall) { callme = whatToCall; } ...
3
votes
4answers
232 views

When should a function take a pointer for a collection to fill vs returning a pointer with a filled collection?

In C++ I frequently see these two signatures used seemingly interchangeably: void fill_array(Array<Type>* array_to_fill); Array<Type>* filled_array(); I imagine there is a subtle ...
3
votes
2answers
505 views

Why dynamic memory allocation functions in C returns void*?

Consider the prototypes of C's dynamic allocation functions malloc - void* malloc(size_t size); calloc - void* calloc(size_t n,size); realloc - void* realloc(void* ptr,size_t newsize); Now a ...