Are vectors passed to functions by value or by reference in C

Question

I m coding in C    If I have some function void foo vector lt int gt  test  and I call it in my program  will the vector be passed by value or reference  I m unsure because I know vectors and arrays are similar and that a function like void bar int test    would pass test in by reference  pointer   instead of by value  My guess is that I would need to pass the vector by pointer reference explicitly if I wanted to avoid passing by value but I m not sure

User · Answer

void foo vector lt int gt  test   vector would be passed by value in this   You have more ways to pass vectors depending on the context -  1  Pass by reference - This will let function foo change your contents of the vector  More efficient than pass by value as copying of vector is avoided   2  Pass by const-reference - This is efficient as well as reliable when you don t want function to change the contents of the vector

User · Answer

when we pass vector by value in a function as an argument it simply creates the copy of vector and no any effect happens on the vector which is defined in main function when we call that particular function  while when we pass vector by reference whatever is written in that particular function  every action will going to perform on the vector which is defined in main or other function when we call that particular function

User · Answer

If I had to guess  I d say that you re from a Java background  This is C    and things are passed by value unless you specify otherwise using the  amp -operator  note that this operator is also used as the  address-of  operator  but in a different context   This is all well documented  but I ll re-iterate anyway   void foo vector lt int gt  bar      by value void foo vector lt int gt   amp bar      by reference  non-const  so modifiable inside foo  void foo vector lt int gt  const  amp bar      by const-reference   You can also choose to pass a pointer to a vector  void foo vector lt int gt   bar    but unless you know what you re doing and you feel that this is really is the way to go  don t do this   Also  vectors are not the same as arrays  Internally  the vector keeps track of an array of which it handles the memory management for you  but so do many other STL containers  You can t pass a vector to a function expecting a pointer or array or vice versa  you can get access to  pointer to  the underlying array and use this though   Vectors are classes offering a lot of functionality through its member-functions  whereas pointers and arrays are built-in types  Also  vectors are dynamically allocated  which means that the size may be determined and changed at runtime  whereas the C-style arrays are statically allocated  its size is constant and must be known at compile-time   limiting their use   I suggest you read some more about C   in general  specifically array decay   and then have a look at the following program which illustrates the difference between arrays and pointers   void foo1 int  arr    cout  lt  lt  sizeof arr   lt  lt    n     void foo2 int arr      cout  lt  lt  sizeof arr   lt  lt    n     void foo3 int arr 10     cout  lt  lt  sizeof arr   lt  lt    n     void foo4 int   amp arr  10     cout  lt  lt  sizeof arr   lt  lt    n      int main         int arr 10     1  2  3  4  5  6  7  8  9  10       foo1 arr       foo2 arr       foo3 arr       foo4 arr

User · Answer

A vector is functionally same as an array  But  to the language vector is a type  and int is also a type  To a function argument  an array of any type  including vector    is treated as pointer  A vector lt int gt  is not same as int    to the compiler   vector lt int gt  is non-array  non-reference  and non-pointer - it is being passed by value  and hence it will call copy-constructor    So  you must use vector lt int gt  amp   preferably with const  if function isn t modifying it  to pass it as a reference

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