Difference between ref and out parameters in NET

Question

What is the difference between ref and out parameters in  NET  What are the situations where one can be more useful than the other  What would be a code snippet where one can be used and another can t

User · Answer

Ref parameters aren t required to be set in the function  whereas out parameters must be bound to a value before exiting the function  Variables passed as out may also be passed to a function without being initialized

User · Answer

The ref keyword is used to pass values by reference   This does not preclude the passed values being value-types or reference types   Output parameters specified with the out keyword are for returning values from a method   One key difference in the code is that you must set the value of an output parameter within the method  This is not the case for ref parameters   For more details look at http   www blackwasp co uk CSharpMethodParameters aspx

User · Answer

out parameters are initialized by the method called  ref parameters are initialized before calling the method   Therefore  out parameters are used when you just need to get a secondary return value  ref parameters are used to get a value and potentially return a change to that value  secondarily to the main return value

User · Answer

out and ref are exactly the same with the exception that out variables don t have to be initialized before sending it into the abyss  I m not that smart  I cribbed that from the MSDN library      To be more explicit about their use  however  the meaning of the modifier is that if you change the reference of that variable in your code  out and ref will cause your calling variable to change reference as well  In the code below  the ceo variable will be a reference to the newGuy once it returns from the call to doStuff  If it weren t for ref  or out  the reference wouldn t be changed   private void newEmployee         Person ceo   Person FindCEO        doStuff ref ceo      private void doStuff ref Person employee        Person newGuy   new Person        employee   newGuy

User · Answer

They are subtly different    An out parameter does not need to be initialized by the callee before being passed to the method  Therefore  any method with an out parameter   Cannot read the parameter before assigning a value to it Must assign a value to it before returning   This is used for a method which needs to overwrite its argument regardless of its previous value     A ref parameter must be initialized by the callee before passing it to the method  Therefore  any method with a ref parameter   Can inspect the value before assigning it Can return the original value  untouched   This is used for a method which must  e g   inspect its value and validate it or normalize it

User · Answer

ref will probably choke on null since it presumably expects to be modifying an existing object   out expects null  since it s returning a new object

User · Answer

This The out and ref Paramerter in C  has some good examples   The basic difference outlined is that out parameters don t need to be initialized when passed in  while ref parameters do

User · Answer

A ref variable needs to be initialized before passing it in  An out variable needs to be set in your function implementation out parameters can be thought of as additional return variables  not input  ref parameters can be thought of as both input and output variables

User · Answer

Example for OUT   Variable gets value initialized after going into the method  Later the same value is returned to the main method   namespace outreftry       class outref               static void Main string   args                        yyy a   new yyy                      u can try giving int i 100 but is useless as that value is not passed into                the method  Only variable goes into the method and gets changed its                value and comes out               int i                a abc out i                System Console WriteLine i                       class yyy                public void abc out int i                         i   10                           Output         10                                                    Example for Ref   Variable should be initialized before going into the method  Later same value or modified value will be returned to the main method   namespace outreftry       class outref               static void Main string   args                        yyy a   new yyy                   int i   0               a abc ref i                System Console WriteLine i                       class yyy                public void abc ref int i                        System Console WriteLine i               i   10                           Output        0     10                                       Hope its clear now

User · Answer

out   In C   a method can return only one value  If you would like to return more than one value  you can use the out keyword  The out modifier returns as return-by-reference  The simplest answer is that the keyword    out    is used to get the value from the method    You don t need to initialize the value in the calling function  You must assign the value in the called function  otherwise the compiler will report an error    ref   In C   when you pass a value type such as int  float  double etc  as an argument to the method parameter  it is passed by value  Therefore  if you modify the parameter value  it does not affect argument in the method call  But if you mark the parameter with    ref    keyword  it will reflect in the actual variable    You need to initialize the variable before you call the function  It   s not mandatory to assign any value to the ref parameter in the method  If you don   t change the value  what is the need to mark it as    ref

User · Answer

They re pretty much the same - the only difference is that a variable you pass as an out parameter doesn t need to be initialized but passing it as a ref parameter it has to be set to something   int x  Foo out x      OK  int y  Foo ref y      Error  y should be initialized before calling the method   Ref parameters are for data that might be modified  out parameters are for data that s an additional output for the function  eg int TryParse  that are already using the return value for something

User · Answer

ref and out both allow the called method to modify a parameter  The difference between them is what happens before you make the call   ref means that the parameter has a value on it before going into the function  The called function can read and or change the value any time  The parameter goes in  then comes out  out means that the parameter has no official value before going into the function  The called function must initialize it  The parameter only goes out   Here s my favorite way to look at it  ref is to pass variables by reference  out is to declare a secondary return value for the function  It s like if you could write this     This is not C  public  bool  string  GetWebThing string name  ref Buffer paramBuffer       This is C  public bool GetWebThing string name  ref Buffer paramBuffer  out string actualUrl    Here s a more detailed list of the effects of each alternative  Before calling the method  ref  The caller must set the value of the parameter before passing it to the called method  out  The caller method is not required to set the value of the argument before calling the method  Most likely  you shouldn t  In fact  any current value is discarded  During the call  ref  The called method can read the argument at any time  out  The called method must initialize the parameter before reading it  Remoted calls  ref  The current value is marshalled to the remote call  Extra performance cost  out  Nothing is passed to the remote call  Faster  Technically speaking  you could use always ref in place of out  but out allows you to be more precise about the meaning of the argument  and sometimes it can be a lot more efficient

User · Answer

Example for OUT   Variable gets value initialized after going into the method  Later the same value is returned to the main method   namespace outreftry       class outref               static void Main string   args                        yyy a   new yyy                      u can try giving int i 100 but is useless as that value is not passed into                the method  Only variable goes into the method and gets changed its                value and comes out               int i                a abc out i                System Console WriteLine i                       class yyy                public void abc out int i                         i   10                           Output         10                                                    Example for Ref   Variable should be initialized before going into the method  Later same value or modified value will be returned to the main method   namespace outreftry       class outref               static void Main string   args                        yyy a   new yyy                   int i   0               a abc ref i                System Console WriteLine i                       class yyy                public void abc ref int i                        System Console WriteLine i               i   10                           Output        0     10                                       Hope its clear now

User · Answer

out specifies that the parameter is an output parameters  i e  it has no value until it is explicitly set by the method   ref specifies that the value is a reference that has a value  and whose value you can change inside the method

User · Answer

Why does C  have both  ref  and  out    The caller of a method which takes an out parameter is not required to assign to the variable passed as the out parameter prior to the call  however  the callee is required to assign to the out parameter before returning   In contrast ref parameters are considered initially assigned by the caller  As such  the callee is not required to assign to the ref parameter before use  Ref parameters are passed both into and out of a method   So  out means out  while ref is for in and out    These correspond closely to the  out  and  in out  parameters of COM interfaces  the advantages of out parameters being that callers need not pass a pre-allocated object in cases where it is not needed by the method being called - this avoids both the cost of allocation  and any cost that might be associated with marshaling  more likely with COM  but not uncommon in  NET

User · Answer

An out parameter is a ref parameter with a special Out   attribute added   If a parameter to a C  method is declared as out  the compiler will require that the parameter be written before it can be read and before the method can return   If C  calls a method whose parameter includes an Out   attribute  the compiler will  for purposes of deciding whether to report  undefined variable  errors  pretend that the variable is written immediately before calling the method   Note that because other  net languages do not attach the same meaning to the Out   attribute  it is possible that calling a routine with an out parameter will leave the variable in question unaffected   If a variable is used as an out parameter before it is definitely assigned  the C  compiler will generate code to ensure that it gets cleared at some point before it is used  but if such a variable leaves and re-enters scope  there s no guarantee that it will be cleared again

User · Answer

out has gotten a new more succint syntax in C 7 https   docs microsoft com en-us dotnet articles csharp whats-new csharp-7 more-expression-bodied-members and even more exciting is the C 7 tuple enhancements that are a more elegant choice than using ref and out IMHO

User · Answer

Ref and Out Parameters   The out and the ref parameters are used to return values in the same variable  that you pass as an argument of a method  These both parameters are very useful when your method needs to return more than one value   You must assigned value to out parameter in calee method body  otherwise the method won t get compiled        Ref Parameter   It has to be initialized before passing to the Method     The ref keyword on a method parameter causes a method to refer to the same variable that was passed as an input parameter for the same method  If you do any changes to the variable  they will be reflected in the variable    int sampleData   0   sampleMethod ref sampleData      Ex of Ref Parameter  public static void Main        int i   3     Variable need to be initialized   sampleMethod ref i         public static void sampleMethod ref int sampleData       sampleData               Out Parameter   It is not necessary to be initialized before passing to Method     The out parameter can be used to return the values in the same variable passed as a parameter of the method  Any changes made to the parameter will be reflected in the variable    int sampleData    sampleMethod out sampleData      Ex of Out Parameter  public static void Main        int i  j     Variable need not be initialized   sampleMethod out i  out j       public static int sampleMethod out int sampleData1  out int sampleData2       sampleData1   10    sampleData2   20    return 0

[c#] Difference between ref and out parameters in .NET

Examples related to c#

Examples related to .net