How do I initialize an empty array in C

Question

Is it possible to create an empty array without specifying the size   For example  I created   String   a   new String 5     Can we create the above string array without the size

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You can define array size at runtime   This will allow you to do whatever to dynamically compute the array s size  But  once defined the size is immutable   Array a   Array CreateInstance typeof string   5

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You could inititialize it with a size of 0  but you will have to reinitialize it  when you know what the size is  as you cannot append to the array   string   a   new string 0

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If you are going to use a collection that you don t know the size of in advance  there are better options than arrays   Use a List lt string gt  instead - it will allow you to add as many items as you need and if you need to return an array  call ToArray   on the variable   var listOfStrings   new List lt string gt         do stuff     string   arrayOfStrings   listOfStrings ToArray      If you must create an empty array you can do this   string   emptyStringArray   new string 0

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In  NET 4 6 the preferred way is to use a new method  Array Empty   String   a   Array Empty lt string gt       The implementation is succinct  using how static members in generic classes behave in  Net   public static T   Empty lt T gt          return EmptyArray lt T gt  Value        Useful in number of places that return an empty byte array to avoid    unnecessary memory allocation  internal static class EmptyArray lt T gt        public static readonly T   Value   new T 0        code contract related code removed for clarity   See also    Array Empty source code on Reference Source Introduction to Array Empty lt T gt    Marc Gravell - Allocaction  Allocation  Allocation - my favorite post on tiny hidden allocations

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Combining  nawfal  amp   Kobi suggestions   namespace Extensions            lt summary gt  Useful in number of places that return an empty byte array to avoid unnecessary memory allocation   lt  summary gt      public static class Array lt T gt                public static readonly T   Empty   new T 0             Usage example   Array lt string gt  Empty   UPDATE 2019-05-14    credits to  Jaider ty   Better use  Net API    public static T   Empty lt T gt        https   docs microsoft com en-us dotnet api system array empty view netframework-4 8  Applies to    NET Core           3 0 Preview 5 2 2 2 1 2 0 1 1 1 0    NET Framework      4 8 4 7 2 4 7 1 4 7 4 6 2 4 6 1 4 6    NET Standard       2 1 Preview 2 0 1 6 1 5 1 4 1 3       HTH

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Here is a real world example  In this it is necessary to initialize the array foundFiles first to zero length    As emphasized in other answers  This initializes not an element and especially not an element with index zero because that would mean the array had length 1  The array has zero length after this line     If the part   string 0  is omitted  there is a compiler error   This is because of the catch block without rethrow  The C  compiler recognizes the code path  that the function Directory GetFiles   can throw an Exception  so that the array could be uninitialized   Before anyone says  not rethrowing the exception would be bad error handling  This is not true  Error handling has to fit the requirements   In this case it is assumed that the program should continue in case of a directory which cannot be read  and not break- the best example is a function traversing through a directory structure  Here the error handling is just logging it  Of course this could be done better  e g  collecting all directories with failed GetFiles Dir  calls in a list  but this will lead too far here   It is enough to state that avoiding throw is a valid scenario  and so the array has to be initialized to length zero  It would be enough to do this in the catch block  but this would be bad style   The call to GetFiles Dir  resizes the array   string   foundFiles  new string 0   string dir     c     try       foundFiles   Directory GetFiles dir       Remark  Array is resized from length zero      Please add appropriate Exception handling yourself catch  IOException      Console WriteLine  Log  Warning  IOException while reading directory      dir        throw     This would throw Exception to caller and avoid compiler error    foreach  string filename in foundFiles      Console WriteLine  Filename      filename

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Simple and elegant   string   array

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string   a   new string 0    or short notation   string   a          The preferred way now is   var a   Array Empty lt string gt      I have written a short regular expression that you can use in Visual Studio if you want to replace zero-length allocations e g  new string 0   Use Find  search  in Visual Studio with Regular Expression option turned on   new    a-zA-Z0-9    0     Now Find All or F3  Find Next  and replace all with Array Empty lt

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I had tried   string   sample   new string 0     But I could only insert one string into it  and then I got an exceptionOutOfBound error  so I just simply put a size for it  like  string   sample   new string 100     Or another way that work for me   List lt string gt  sample   new List lt string gt       Assigning Value for list   sample Add your input

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There is not much point in declaring an array without size  An array is about size  When you declare an array of specific size  you specify the fixed number of slots available in a collection that can hold things  and accordingly memory is allocated  To add something to it  you will need to anyway reinitialize the existing array  even if you re resizing the array  see this thread   One of the rare cases where you would want to initialise an empty array would be to pass array as an argument   If you want to define a collection when you do not know what size it could be of possibly  array is not your choice  but something like a List lt T gt  or similar   That said  the only way to declare an array without specifying size is to have an empty array of size 0  hemant and Alex Dn provides two ways  Another simpler alternative is to just   string   a           The elements inside the bracket should be implicitly convertible to type defined  for instance  string   a      a    b       Or yet another   var a   Enumerable Empty lt string gt    ToArray      Here is a more declarative way   public static class Array lt T gt        public static T   Empty                 return Empty 0              public static T   Empty int size                return new T size             Now you can call   var a   Array lt string gt  Empty       or  var a   Array lt string gt  Empty 5

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Try this    string   a   new string

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As I know you can t make array without size  but you can use   List lt string gt  l   new List lt string gt       and then l ToArray

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You can do   string   a     String Empty      Note  OP meant not having to specify a size  not make an array sizeless

[c#] How do I initialize an empty array in C#?

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