Meaning of referencing and dereferencing in C

Question

I read different things on the Internet and got confused  because every website says different things   I read about   referencing operator and  amp  dereferencing operator  or that referencing means making a pointer point to a variable and dereferencing is accessing the value of the variable that the pointer points to  So I got confused     Can I get a simple but thorough explanation about  referencing and dereferencing

User · Answer

I ve always heard them used in the opposite sense     amp  is the reference operator -- it gives you a reference  pointer  to some object   is the dereference operator -- it takes a reference  pointer  and gives you back the referred to object

User · Answer

For a start  you have them backwards   amp  is reference and   is dereference    Referencing a variable means accessing the memory address of the variable   int i   5  int   p  p    amp i     amp i returns the memory address of the variable i    Dereferencing a variable means accessing the variable stored at a memory address   int i   5  int   p  p    amp i   p   7     p returns the variable stored at the memory address stored in p  which is i    i is now 7

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Referencing  amp  is the reference operator  It will refer the memory address to the pointer variable  Example  int  p  int a 5  p  amp a     Here Pointer variable p refers to the address of integer variable a   Dereferencing Dereference operator   is used by the pointer variable to directly access the value of the variable instead of its memory address  Example  int  p  int a 5  p  amp a  int value  p     Value variable will get the value of variable a that pointer variable p pointing to

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Reference of the de-referenced pointer is also same as the address of the pointed variable  Explanation  - int var   3  int  p  p    amp var  so  let s think address of var is   ABCDE then  p   ABCDE and  amp  p   ABCDE  that means put  amp   together  neutral the referencing and de-referencing   also when declaring a function   the function s arguments should be the pointers  and in the arguments of the this function when calling it in main method are should been with  amp  operator  it s bit confusing  But remember that int  p    amp var   is also correct as the above pointer declaration

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Referencing means taking the address of an existing variable   using  amp   to set a pointer variable  In order to be valid  a pointer has to be set to the address of a variable of the same type as the pointer  without the asterisk   int  c1  int  p1  c1   5  p1    amp c1    p1 references c1   Dereferencing a pointer means using the   operator  asterisk character  to retrieve the value from the memory address that is pointed by the pointer  NOTE  The value stored at the address of the pointer must be a value OF THE SAME TYPE as the type of variable the pointer  points  to  but there is no guarantee this is the case unless the pointer was set correctly   The type of variable the pointer points to is the type less the outermost asterisk   int n1  n1    p1    Invalid dereferencing may or may not cause crashes   Dereferencing an uninitialized pointer can cause a crash Dereferencing with an invalid type cast will have the potential to cause a crash   Dereferencing a pointer to a variable that was dynamically allocated and was subsequently de-allocated can cause a crash Dereferencing a pointer to a variable that has since gone out of scope can also cause a crash    Invalid referencing is more likely to cause compiler errors than crashes  but it s not a good idea to rely on the compiler for this   References   http   www codingunit com cplusplus-tutorial-pointers-reference-and-dereference-operators   amp  is the reference operator and can be read as    address of       is the dereference operator and can be read as    value pointed by       http   www cplusplus com doc tutorial pointers    amp  is the reference operator       is the dereference operator   http   en wikipedia org wiki Dereference operator  The dereference operator   is also called the indirection operator

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find the below explanation   int main         int a   10    say address of  a  is 2000      int  p    amp a    it means  p  is pointing referencing  to  a   i e p- gt 2000     int c    p     p means dereferncing  it will give the content of the address pointed by  p   in this case  p  is pointing to 2000 address of  a  variable   content of 2000 is 10  so  p will give 10       conclusion      amp   address operator  is used for referencing     star operator  is used for de-referencing

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The context that   is in  confuses the meaning sometimes         when declaring a function int function int       This function is being declared as a function that takes in an  address  that holds a number  so int    it s asking for a  reference   interchangeably called  address   When I  call  use  this function later  I better give it a variable-address  So instead of var  or q  or w  or p  I give it the address of var so  amp var  or  amp q  or  amp w  or  amp p        even though the symbol       is typically used to mean  dereferenced variable  meaning  to use the value at the address of a variable --despite it s common use  in this case  the symbol means a  reference   again  in THIS context   context here being the declaration of a  prototype             when calling a function int main         function  amp var       we are giving the function a  reference   we are giving it an  address        So  in the context of declaring a type such as int or char  we would use the dereferencer       to actually mean the reference  the address   which makes it confusing if you see an error message from the compiler saying   expecting char   which is asking for an address   In that case  when the   is after a type  int  char  etc   the compiler is expecting a variable s address  We give it this by using a reference operator  alos called the address-of operator    amp    before a variable  Even further  in the case I just made up above  the compiler is expecting the address to hold a character value  not a number   type char      address of a value that has a character   int  p  int  a       both are  pointer  declarations  We are telling the compiler that we will soon give these variables an address  with  amp     int c   10     declare and initialize a random variable   assign the variable to a pointer  we do this so that we can modify the value of c from a different function regardless of the scope of that function  elaboration in a second   p   c    ERROR  we assigned a  value  to this  pointer   We need to assign an  address   a  reference   p    amp c     instead of a value such as   q  5  t   or 2 1 we gave the pointer an  address   which we could actually print with printf    and would be something like   so p   0xab33d111    the address of c   not specifically this value for the address  it ll look like this though  with the 0x in the beggining  the computer treats these different from regular numbers   p   10     the value of c  a    amp c     I can still give c another pointer  even though it already has the pointer variable  p    a   10   a   0xab33d111    Think of each variable as having a position  or an index value if you are familiar with arrays  and a value  It might take some getting used-to to think of each variable having two values to it  one value being it s position  physically stored with electricity in your computer  and a value representing whatever quantity or letter s  the programmer wants to store     Why it s used int function b       b   b   1     we just want to add one to any variable that this function operates on      int main         int c   1      I want this variable to be 3       function c        function c     I call the function I made above twice  because I want c to be 3           this will return c as 1  Even though I called it twice          when you call a function it makes a copy of the variable          so the function that I call  function   made a copy of c  and that function is only changing the  copy  of c  so it doesn t affect the original       let s redo this whole thing  and use pointers  int function int  b      this time  the function is  asking   won t run without  for a variable that  points  to a number-value  int   So it wants an integer pointer--an address that holds a number   b    b   1    grab the value of the address  and add one to the value stored at that address    int main        int c   1    again  I want this to be three at the end of the program     int  p    amp c     on the left  I m declaring a pointer  I m telling the compiler that I m about to have this letter point to an certain spot in my computer  Immediately after I used the assignment operator  the        to assign the address of c to this variable  pointer in this case  p  I do this using the address-of operator  referencer    amp         function p      not  p  because that will dereference  which would give an integer  not an integer pointer   function wants a reference to an int called int   we aren t going to use  p because that will give the function an int instead of an address that stores an int       function  amp c      this is giving the same thing as above  p   the address of c  so we can pass the  pointer  or we can pass the  address  that the pointer variable  is  pointing   referencing  to  Which is  amp c  0xaabbcc1122              now  the function is making a copy of c s address  but it doesn t matter if it s a copy or not  because it s going to point the computer to the exact same spot  hence  The Address   and it will be changed for main s version of c as well       Inside each and every block  it copies the variables  if any  that are passed into  via parameters within     s   Within those blocks  the changes to a variable are made to a copy of that variable  the variable uses the same letters but is at a different address  from the original   By using the address  reference  of the original  we can change a variable using a block outside of main  or inside a child of main

[c] Meaning of "referencing" and "dereferencing" in C

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