What is the difference between the dot operator and - in C

Question

What is the difference between the dot     operator and -   in C

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pSomething- gt someMember   is equivalent to    pSomething  someMember

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It s simple  whenever you see   x- gt y   know it is the same as     x  y

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The    dot  operator is usually used to get a field   call a method from an instance of class  or a static field   method of a class    p myField  p myMethod   - p instance of a class  The -   arrow  operator is used to get a field   call a method from the content pointed by the class   p- myField  p- myMethod   - p points to a class

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For a pointer  we could just use   pointervariable foo   But the   operator has greater precedence than the   operator  so   is evaluated first  So we need to force this with parenthesis     pointervariable  foo   But typing the    s all the time is hard  so they developed - gt  as a shortcut to say the same thing  If you are accessing a property of an object or object reference  use    If you are accessing a property of an object through a pointer  use - gt

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Dot operator can t be overloaded  arrow operator can be overloaded  Arrow operator is generally meant to be applied to pointers  or objects that behave like pointers  like smart pointers   Dot operator can t be applied to pointers   EDIT When applied to pointer arrow operator is equivalent to applying dot operator to pointee e g  ptr- gt field is equivalent to   ptr  field

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The arrow operator is like dot  except it dereferences a pointer first  foo bar   calls method bar   on object foo  foo- gt bar calls method bar on the object pointed to by pointer foo

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The   operator is for direct member access   object Field   The arrow dereferences a pointer so you can access the object memory it is pointing to  pClass- gt Field

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The target  dot works on objects  arrow works on pointers to objects   std  string str  foo    std  string   pstr   new std  string  foo     str size     pstr- gt size

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The simplest difference between the two is that   -   dereferences a pointer before it goes to look at that objects fields  function etc  whereas     doesn t dereference first  Use  -   when you have a pointer to an object  and use     when you re working with the actual instance of an object   Another equivalent way of wrinting this might be to use the dereferencing     on the pointer first and then just use the      We skip middleman by using  -     There are other differences  but the other answers have covered this extensively   If you have a background in Java this might confuse you  since  in Java  everything is pointers  This means that there s no reason to have symbol that doesn t dereference your pointer first  In c   however you gotta be a little more careful with remembering what is and what isn t a pointer  and it might be a good idea to label them with the prefix  p   or simply  p

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Note that the -  operator cannot be used for certain things  for instance  accessing operator      include  lt vector gt   int main        std  vector lt int gt  iVec     iVec push back 42      std  vector lt int gt   iVecPtr    amp iVec        int i   iVecPtr- gt  0      Does not compile    int i     iVecPtr  0      Compiles

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The -  is simply syntactic sugar for a pointer dereference   As others have said   pointer- method     is a simple method of saying     pointer  method     For more pointer fun  check out Binky  and his magic wand of dereferencing   http   www youtube com watch v UvoHwFvAvQE

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Use - gt  when you have a pointer  Use   when you have structure  class    When you want to point attribute that belongs to structure use     structure attribute   When you want to point to an attribute that has reference to memory by pointer use - gt     pointer- gt method    or same as     pointer  method

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foo- gt bar   is the same as   foo  bar     The parenthesizes above are necessary because of the binding strength of the   and   operators      foo bar   wouldn t work because Dot     operator is evaluated first  see operator precedence   The Dot     operator can t be overloaded  arrow  - gt   operator can be overloaded   The Dot     operator can t be applied to pointers   Also see  What is the arrow operator  -   synonym for in C

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The -  operator is used when we are working with a pointer and the dot is used otherwise   So if we have a struct class like   struct class  int num students  int yr grad       and we have an instance of a class  curr class  class pointer    then to get access to number of students we would do   cout  lt  lt  curr class- gt num students  lt  lt  endl    In case we had a simple class object   say class 2016  we would do   cout  lt  lt  class 2016 num students  lt  lt  endl    For the pointer to class the -  operator is equivalent to     obj  mem var   Note  For a class  the way to access member functions of the class will also be the same way

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