Calling the base constructor in C

Question

If I inherit from a base class and want to pass something from the constructor of the inherited class to the constructor of the base class  how do I do that   For example  if I inherit from the Exception class I want to do something like this   class MyExceptionClass   Exception        public MyExceptionClass string message  string extraInfo                    This is where it s all falling apart          base message              Basically what I want is to be able to pass the string message to the base Exception class

User · Answer

It is true use the base  something  to call the base class constructor  but in case of overloading use the this keyword  public ClassName     this par1 par2       do not call the constructor it is called in the this     the base key- word is used to call a inherited constructor           Hint used overload as often as needed do not write the same code 2 or more times

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class Exception        public Exception string message                                  class MyExceptionClass   Exception        public MyExceptionClass string message  string extraInfo         base message

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Note that you can use static methods within the call to the base constructor   class MyExceptionClass   Exception        public MyExceptionClass string message  string extraInfo              base ModifyMessage message  extraInfo                       private static string ModifyMessage string message  string extraInfo                  Trace WriteLine  message was     message            return message ToLowerInvariant     Environment NewLine   extraInfo

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public class MyException   Exception       public MyException           public MyException string msg    base msg          public MyException string msg  Exception inner    base msg  inner

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If you need to call the base constructor but not right away because your new  derived  class needs to do some data manipulation  the best solution is to resort to factory method  What you need to do is to mark private your derived constructor  then make a static method in your class that will do all the necessary stuff and later call the constructor and return the object   public class MyClass   BaseClass       private MyClass string someString    base someString                  your code goes in here            public static MyClass FactoryMethod string someString                  whatever you want to do with your string before passing it in         return new MyClass someString

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public class Car        public Car string model                 Console WriteLine model             public class Mercedes   Car        public Mercedes string model   base model                     Usage   Mercedes mercedes   new Mercedes  CLA Shooting Brake      Output  CLA Shooting Brake

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Using newer C  features  namely out var  you can get rid of the static factory-method  I just found out  by accident  that out var parameter of methods called inse base- call  flow to the constructor body   Example  using this base class you want to derive from   public abstract class BaseClass       protected BaseClass int a  int b  int c                  The non-compiling pseudo code you want to execute   public class DerivedClass   BaseClass       private readonly object fatData       public DerivedClass int m                var fd   new   A   1   m  B   2   m  C   3   m            base fd A  fd B  fd C      base-constructor call         this fatData   fd            And the solution by using a static private helper method which produces all required base arguments  plus additional data if needed  and without using a static factory method  just plain constructor to the outside   public class DerivedClass   BaseClass       private readonly object fatData       public DerivedClass int m            base PrepareBaseParameters m  out var b  out var c  out var fatData   b  c                this fatData   fatData          Console WriteLine new   b  c  fatData   ToString                private static int PrepareBaseParameters int m  out int b  out int c  out object fatData                var fd   new   A   1   m  B   2   m  C   3   m             b  c  fatData     fd B  fd C  fd      Tuples not required but nice to use         return fd A

User · Answer

Modify your constructor to the following so that it calls the base class constructor properly   public class MyExceptionClass   Exception       public MyExceptionClass string message  string extrainfo    base message                  other stuff here           Note that a constructor is not something that you can call anytime within a method  That s the reason you re getting errors in your call in the constructor body

User · Answer

As per some of the other answers listed here  you can pass parameters into the base class constructor   It is advised to call your base class constructor at the beginning of the constructor for your inherited class   public class MyException   Exception       public MyException string message  string extraInfo    base message                  I note that in your example you never made use of the extraInfo parameter  so I assumed you might want to concatenate the extraInfo string parameter to the Message property of your exception  it seems that this is being ignored in the accepted answer and the code in your question    This is simply achieved by invoking the base class constructor  and then updating the Message property with the extra info   public class MyException  Exception       public MyException string message  string extraInfo    base    message  Extra info   extraInfo

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public class MyExceptionClass   Exception       public MyExceptionClass string message        Exception innerException   base message  innerException                  other stuff here           You can pass inner exception to one of the constructors

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You can also do a conditional check with parameters in the constructor  which allows some flexibility   public MyClass object myObject null   base myObject    new myOtherObject          or  public MyClass object myObject null   base myObject  null   new myOtherObject    myObject

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From Framework Design Guidelines and FxCop rules    1  Custom Exception should have a name that ends with Exception      class MyException   Exception   2  Exception should be public      public class MyException   Exception   3  CA1032  Exception should implements standard constructors    A public parameterless constructor  A public constructor with one string argument  A public constructor with one string and Exception  as it can wrap another Exception   A serialization constructor protected if the type is not sealed and private if the type is sealed   Based on MSDN    Serializable    public class MyException   Exception     public MyException               Add any type-specific logic  and supply the default message         public MyException string message   base message               Add any type-specific logic        public MyException string message  Exception innerException         base  message  innerException              Add any type-specific logic for inner exceptions        protected MyException SerializationInfo info        StreamingContext context    base info  context              Implement type-specific serialization constructor logic             or       Serializable        public sealed class MyException   Exception             public MyException                       Add any type-specific logic  and supply the default message                 public MyException string message   base message                       Add any type-specific logic                public MyException string message  Exception innerException             base  message  innerException                      Add any type-specific logic for inner exceptions                private MyException SerializationInfo info            StreamingContext context    base info  context                      Implement type-specific serialization constructor logic

[c#] Calling the base constructor in C#

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