Questions tagged [pointers]

Data types for "pointing" at other values: A pointer's value is a memory address where the pointed-to value is stored. This tag should be used for questions involving the use of pointers, not references. Common programming languages using pointers are C, C++, Go, and assembly and intermediate-representation languages; use a specific language tag. Other helpful tags should describe what is being pointed-to (e.g. a function, a struct etc.)

A pointer is a data type that "points to" another value stored in memory using its address. Using a pointer rather than the pointed-to entity often holds performance benefits in repetitive operations. For example, copying a pointer is very often "cheaper" than copying the value that it points to: The pointee may be a large data structure, or its copying may be non-trivial, involving memory-location dependent values, while with a pointer - only the address must be copied.

Pointers are an important concept in many high-level programming languages, including C and C++. The Wikipedia page on pointers has a fairly in-depth introduction to the concept.

Please consult some of the following content for a more in-depth explanation of pointers.


See also

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44 answers

What are the differences between a pointer variable and a reference variable?

What is the difference between a pointer variable and a reference variable?
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When should static_cast, dynamic_cast, const_cast, and reinterpret_cast be used?

What are the proper uses of: static_cast dynamic_cast const_cast reinterpret_cast (type)value (C-style cast) type(value) (function-style cast) How does one decide which to use in which specific cases?
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What is a smart pointer and when should I use one?

What is a smart pointer and when should I use one?
Alex Reynolds
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Regular cast vs. static_cast vs. dynamic_cast

I've been writing C and C++ code for almost twenty years, but there's one aspect of these languages that I've never really understood. I've obviously used regular casts i.e. MyClass *m = (MyClass *)ptr; all over the place, but there seem to be two…
Graeme Perrow
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Why should I use a pointer rather than the object itself?

I'm coming from a Java background and have started working with objects in C++. But one thing that occurred to me is that people often use pointers to objects rather than the objects themselves, for example this declaration: Object *myObject = new…
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With arrays, why is it the case that a[5] == 5[a]?

As Joel points out in Stack Overflow podcast #34, in C Programming Language (aka: K & R), there is mention of this property of arrays in C: a[5] == 5[a] Joel says that it's because of pointer arithmetic but I still don't understand. Why does a[5] ==…
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What is the difference between const int*, const int * const, and int const *?

I always mess up how to use const int*, const int * const, and int const * correctly. Is there a set of rules defining what you can and cannot do? I want to know all the do's and all don'ts in terms of assignments, passing to the functions, etc.
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How do you pass a function as a parameter in C?

I want to create a function that performs a function passed by parameter on a set of data. How do you pass a function as a parameter in C?
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What does 'dereferencing' a pointer mean in C/C++?

Please include an example with the explanation.
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What exactly is nullptr?

We now have C++11 with many new features. An interesting and confusing one (at least for me) is the new nullptr. Well, no need anymore for the nasty macro NULL. int* x = nullptr; myclass* obj = nullptr; Still, I am not getting how nullptr works.…
Khaled Alshaya
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Typedef function pointer?

I'm learning how to dynamically load DLL's but what I don't understand is this line typedef void (*FunctionFunc)(); I have a few questions. If someone is able to answer them I would be grateful. Why is typedef used? The syntax looks odd; after…
Jack Harvin
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Pointers vs. values in parameters and return values

In Go there are various ways to return a struct value or slice thereof. For individual ones I've seen: type MyStruct struct { Val int } func myfunc() MyStruct { return MyStruct{Val: 1} } func myfunc() *MyStruct { return…
Zef Hemel
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How do I use arrays in C++?

C++ inherited arrays from C where they are used virtually everywhere. C++ provides abstractions that are easier to use and less error-prone (std::vector since C++98 and std::array since C++11), so the need for arrays does not arise quite as…
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How does free know how much to free?

In C programming, you can pass any kind of pointer you like as an argument to free, how does it know the size of the allocated memory to free? Whenever I pass a pointer to some function, I have to also pass the size (ie an array of 10 elements needs…
Joshua Cheek
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C pointer to array/array of pointers disambiguation

What is the difference between the following declarations: int* arr1[8]; int (*arr2)[8]; int *(arr3[8]); What is the general rule for understanding more complex declarations?
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