What is the data type of pointer variables?

Question

I refereed the following link,

Link1 Link 2

In the above link1 it was mentioned in answer that \"Pointers are of pointer type\".

I jus

Answer 1

You've asked two different questions.

Your title asks "What is the data type of pointer variables?". The answer is simple: a pointer variable is of some pointer type. For example, given:

int *ptr;

ptr is a pointer object, and its type is int*, which is a pointer type.

The body of your question asks whether "a pointer is a data type or not". By any reasonable definition of the phrase "data type", pointer types are data types.

The C standard never defines the phrase "data type", but it does use it (informally) in several places. It happens that none of the uses of the phrase "data type" in the standard refer to pointer types, but that doesn't tell us anything.

The standard says that all types are either function types or object types. Object types are further divided into a number of categories: integer types, array types, structure types, union types, pointer types, etc. A pointer type can be a pointer to an object type or a pointer to a function type. (It can be a pointer to an incomplete object type; as of the 2011 standard, incomplete types are classified as object types.)

Another ambiguity in your question is your use of the word "pointer". The word "pointer" by itself commonly refers to an object of pointer type, but it can also refer to a value of pointer type (for example, the standard says that malloc returns a pointer). It's better to use "pointer" as an adjective rather than as a noun, so you can have:

• a pointer type;
• a pointer object (an object of pointer type);
• a pointer expression (an expression that yields a result of pointer type); or
• a pointer value (the value, of pointer type, yielded by a pointer expression).

A pointer type is an object type. A pointer object is an object; an object is defined by the standard as a "region of data storage in the execution environment, the contents of which can represent values". So a pointer object is a region of data storage.

Following your Link 2, some random person on the Internet wrote that "Pointers are simply a variable that hold an address so one could argue that a pointer is a data type, but it is not defined as a data type (per "The C Programming Language". Kernighan & Ritchie)". I don't know whether K&R defines the term "data type"; since this person didn't provide a specific citation, it's difficult to tell without searching the book. But it's the standard, not K&R, that defines the language.

I'm curious: why would you think that a pointer type wouldn't be considered a data type?

Answer 2

Yes, pointer is a data type and a pointer variable store that pointer data type.

Answer 3

Pointer types are data types; they store pointer values.

There is no one single pointer type; a pointer to int is a different type from a pointer to char, which is a different type from a pointer to double, which is a different type from a pointer to a 10-element array of int, which is a different type from a pointer to an 11-element array of int, etc.

Different pointer types may have different sizes and representations; the only pointer types that are guaranteed to have the same sizes and representations are void * and char *.

Answer 4

Pointer is a data-type. So we can create pointer variables which can hold the address of memory location.

Answer 5

Your question probably refers to the "data type of a pointer", in contrast to the data type of the pointed-to data, which is what one would understand in the first place.

Based on this assumption, then please look at type uintptr_t or void*.

To quote Drew Dorman's answer: "uintptr_t is an unsigned integer type that is capable of storing a pointer. Which typically means that it's the same size as a pointer"

Of course, its size is platform-dependant: 32 bit or 64 bit. So don't transport this variable across platforms of different size.

Please note, to assign it you have to cast from the 'specific' pointer type, to the 'generic' one:

int var = 1;
int* addrOfVar = &var; // pointer to variable
uintptr_t pVar = (uintptr_t)&var;
uintptr_t pVar2 = reinterpret_cast<uintptr_t>(&var); // alternative cast

Answer 6

For example in the C Standard there is no formal definition of the term data type. There are object types and function types. At the same time pointers are derived types constructed from object and function types.

Thus in general case pointers are data types that is they are data types that are constructed from object and function types.

Also there is definition of term object in the C Standard

3.15
1 object
region of data storage in the execution environment, the contents of which can represent
values

So there is some contradiction in the Standard. On the one hand pointers are objects because they occupy memory and the memory represents their values. So we may say that pointers are object types. On the other hand pointers are considered as derived types from object types.

In my opinion it would be better if there would be explicitly written in the Standard that pointers are derived object types or derived function types.

In any case you may bravely say that pointers are data types!:)