Pass by pointer Pass by reference

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Possible Duplicate    What are the differences between pointer variable and reference variable in C      Are there benefits of passing by pointer over passing by reference in C          In both cases  I achieved the result  So when is one preferred over the other  What are the reasons we use one over the other    include  lt iostream gt  using namespace std  void swap int  x  int  y        int z    x       x  y       y z    void swap int amp  x  int amp  y        int z   x      x y      y z     int main         int a   45      int b   35      cout lt  lt  Before Swap n       cout lt  lt  a   lt  lt a lt  lt   b   lt  lt b lt  lt   n        swap  amp a  amp b       cout lt  lt  After Swap with pass by pointer n       cout lt  lt  a   lt  lt a lt  lt   b   lt  lt b lt  lt   n        swap a b       cout lt  lt  After Swap with pass by reference n       cout lt  lt  a   lt  lt a lt  lt   b   lt  lt b lt  lt   n       Output  Before Swap a 45 b 35 After Swap with pass by pointer a 35 b 45  After Swap with pass by reference a 45 b 35

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In fact  most compilers emit the same code for both functions calls  because references are generally implemented using pointers   Following this logic  when an argument of  non-const  reference type is used in the function body  the generated code will just silently operate on the address of the argument and it will dereference it  In addition  when a call to such a function is encountered  the compiler will generate code that passes the address of the arguments instead of copying their value   Basically  references and pointers are not very different from an implementation point of view  the main  and very important  difference is in the philosophy  a reference is the object itself  just with a different name   References have a couple more advantages compared to pointers  e  g  they can t be NULL  so they are safer to use   Consequently  if you can use C    then passing by reference is generally considered more elegant and it should be preferred  However  in C  there s no passing by reference  so if you want to write C code  or  horribile dictu  code that compiles with both a C and a C   compiler  albeit that s not a good idea   you ll have to restrict yourself to using pointers

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Pass by pointer is the only way you could pass  by reference  in C  so you still see it used quite a bit   The NULL pointer is a handy convention for saying a parameter is unused or not valid  so use a pointer in that case   References can t be updated once they re set  so use a pointer if you ever need to reassign it   Prefer a reference in every case where there isn t a good reason not to  Make it const if you can

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Use references all the time and pointers only when you have to refer to NULL which reference cannot refer   See this FAQ   http   www parashift com c  -faq-lite references html faq-8 6

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A reference is semantically the following   T amp   lt   gt    T   const   const T amp   lt   gt    T const   const   T amp  amp   lt   gt   no C equivalent   C  11   As with other answers  the following from the C   FAQ is the one-line answer  references when possible  pointers when needed   An advantage over pointers is that you need explicit casting in order to pass NULL  It s still possible  though  Of the compilers I ve tested  none emit a warning for the following   int  p         return 0    void x int amp  y      y   1    int main        x  p

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Here is a good article on the matter -  Use references when you can  and pointers when you have to

[c++] Pass by pointer & Pass by reference

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