What is the size of a pointer

Question

Is the size of a pointer the same as the size as the type its pointing to  or do pointers always have a fixed size   For example     int x   10  int   xPtr    amp x  char y    a   char   yPtr    amp y   std  cout  lt  lt  sizeof x   lt  lt    n   std  cout  lt  lt  sizeof xPtr   lt  lt    n   std  cout  lt  lt  sizeof y   lt  lt    n   std  cout  lt  lt  sizeof yPtr   lt  lt    n     What would the output of this be   Would sizeof xPtr  return 4 and sizeof yPtr  return 1  or would the 2 pointers actually return the same size   The reason I ask this is because the pointers are storing a memory address and not the values of their respective stored addresses

User · Accepted Answer

Pointers generally have a fixed size  for ex  on a 32-bit executable they re usually 32-bit   There are some exceptions  like on old 16-bit windows when you had to distinguish between 32-bit pointers and 16-bit     It s usually pretty safe to assume they re going to be uniform within a given executable on modern desktop OS s   Edit  Even so  I would strongly caution against making this assumption in your code   If you re going to write something that absolutely has to have a pointers of a certain size  you d better check it   Function pointers are a different story -- see Jens  answer for more info

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Recently came upon a case where this was not true  TI C28x boards can have a sizeof pointer    1  since a byte for those boards is 16-bits  and pointer size is 16 bits  To make matters more confusing  they also have far pointers which are 22-bits  I m not really sure what sizeof far pointer would be  In general  DSP boards can have weird integer sizes  So pointer sizes can still be weird in 2020 if you are looking in weird places

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They can be different on word-addressable machines  e g   Cray PVP systems    Most computers today are byte-addressable machines  where each address refers to a byte of memory  There  all data pointers are usually the same size  namely the size of a machine address   On word-adressable machines  each machine address refers instead to a word larger than a byte  On these  a  char    or  void    pointer to a byte of memory has to contain both a word address plus a byte offset within the addresed word   http   docs cray com books 004-2179-001 html-004-2179-001 rvc5mrwh html

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Pointers are not always the same size on the same architecture   You can read more on the concept of  near    far  and  huge  pointers  just as an example of a case where pointer sizes differ     http   en wikipedia org wiki Intel Memory Model Pointer sizes

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On 32-bit machine sizeof pointer is 32 bits   4 bytes   while on 64 bit machine it s 8 byte  Regardless of what data type they are pointing to  they have fixed size

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Function Pointers can have very different sizes  from 4 to 20 Bytes on an X86 machine  depending on the compiler  So the answer is NO - sizes can vary   Another example  take an 8051 program  it has three memory ranges and thus has three different pointer sizes  from 8 bit  16bit  24bit  depending on where the target is located  even though the target s size is always the same  e g  char

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To answer your other question  The size of a pointer and the size of what it points to are not related  A good analogy is to consider them like postal addresses  The size of the address of a house has no relationship to the size of the house

User · Answer

The size of a pointer is the size required by your system to hold a unique memory address  since a pointer just holds the address it points to

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