const int vs int const as function parameters in C and C

Question

Consider   int testfunc1  const int a      return a     int testfunc2  int const a      return a      Are these two functions the same in every aspect or is there a difference   I m interested in an answer for the C language  but if there is something interesting in the C   language  I d like to know as well

User · Answer

I think in this case they are the same  but here is an example where order matters   const int  cantChangeTheData  int  const cantChangeTheAddress

User · Answer

const int is identical to int const  as is true with all scalar types in C   In general  declaring a scalar function parameter as const is not needed  since C s call-by-value semantics mean that any changes to the variable are local to its enclosing function

User · Answer

They are the same  but in C   there s a good reason to always use const on the right  You ll be consistent everywhere because const member functions must be declared this way   int getInt   const    It changes the this pointer in the function from Foo   const to Foo const   const  See here

User · Answer

The trick is to read the declaration backwards  right-to-left    const int a   1     read as  a is an integer which is constant  int const a   1     read as  a is a constant integer    Both are the same thing  Therefore   a   2     Can t do because a is constant   The reading backwards trick especially comes in handy when you re dealing with more complex declarations such as   const char  s          read as  s is a pointer to a char that is constant  char c  char  const t    amp c     read as  t is a constant pointer to a char    s    A      Can t do because the char is constant s            Can do because the pointer isn t constant  t    A      Can do because the char isn t constant t            Can t do because the pointer is constant

User · Answer

This isn t a direct answer but a related tip   To keep things straight  I always use the convection  put const on the outside   where by  outside  I mean the far left or far right  That way there is no confusion -- the const applies to the closest thing  either the type or the     E g      int   const foo           Pointer cannot change  pointed to value can change const int   bar           Pointer can change  pointed to value cannot change int   baz           Pointer can change  pointed to value can change const int   const qux           Pointer cannot change  pointed to value cannot change

User · Answer

Prakash is correct that the declarations are the same  although a little more explanation of the pointer case might be in order    const int  p  is a pointer to an int that does not allow the int to be changed through that pointer    int  const p  is a pointer to an int that cannot be changed to point to another int   See https   isocpp org wiki faq const-correctness const-ptr-vs-ptr-const

User · Answer

const T and T const are identical  With pointer types it becomes more complicated    const char  is a pointer to a constant char char const  is a pointer to a constant char char  const is a constant pointer to a  mutable  char   In other words   1  and  2  are identical  The only way of making the pointer  rather than the pointee  const is to use a suffix-const   This is why many people prefer to always put const to the right side of the type     East const    style   it makes its location relative to the type consistent and easy to remember  it also anecdotally seems to make it easier to teach to beginners

User · Answer

Yes  they are same for just int  and different for int

User · Answer

There is no difference   They both declare  a  to be an integer that cannot be changed   The place where differences start to appear is when you use pointers   Both of these   const int  a int const  a   declare  a  to be a pointer to an integer that doesn t change    a  can be assigned to  but   a  cannot   int   const a   declares  a  to be a constant pointer to an integer     a  can be assigned to  but  a  cannot   const int   const a   declares  a  to be a constant pointer to a constant integer   Neither  a  nor   a  can be assigned to   static int one   1   int testfunc3  const int  a       a   1     Error      a    amp one    return  a     int testfunc4  int   const a       a   1    a    amp one     Error      return  a     int testfunc5  const int   const a       a   1       Error      a    amp one     Error      return  a

User · Answer

const int is identical to int const  as is true with all scalar types in C   In general  declaring a scalar function parameter as const is not needed  since C s call-by-value semantics mean that any changes to the variable are local to its enclosing function

[c++] 'const int' vs. 'int const' as function parameters in C++ and C

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