If Array Length 0

Question

If an array is empty  it looks like you can t check it s length using   length    What s the best way to check if an array is empty

User · Answer

Since  Net  gt   5 0 the best way is to use Any  if  array Any           now you sure it s empty    For nullable arrays  if   array  Any      true          now you sure it s null or empty

User · Answer

If array is null  trying to derefrence array Length will throw a NullReferenceException  If your code considers null to be an invalid value for array  you should reject it and blame the caller  One such pattern is to throw ArgumentNullException   void MyMethod string   array        if  array    null  throw new ArgumentNullException nameof array         if  array Length  gt  0                   Do something with array              If you want to accept a null array as an indication to not do something or as an optional parameter  you may simply not access it if it is null   void MyMethod string   array        if  array    null                   Do something with array here              If you want to avoid touching array when it is either null or has zero length  then you can check for both at the same time with C -6   s null coalescing operator   void MyMethod string   array        if  array  Length  gt  0                   Do something with array              Superfluous Length Check  It seems strange that you are treating the empty array as a special case  In many cases  if you  e g   would just loop over the array anyway  there   s no need to treat the empty array as a special case  foreach  var elem in array     body    will simply never execute   body   when array Length is 0  If you are treating array    null    array Length    0 specially to  e g   improve performance  you might consider leaving a comment for posterity  Otherwise  the check for Length    0 appears superfluous   Superfluous code makes understanding a program harder because people reading the code likely assume that each line is necessary to solve some problem or achieve correctness  If you include unnecessary code  the readers are going to spend forever trying to figure out why that line is or was necessary before deleting it  -

User · Answer

Your suggested test is fine  so long as the array is intialised     Martin

User · Answer

You can use  Length    0 if the length is empty and the array exists  but are you sure it s not null

User · Answer

Yeah  for safety I would probably do   if array    null    array Length    0

User · Answer

check if the array is null first so you would avoid a null pointer exception  logic in any language  if array is null or is empty  do

User · Answer

This is the best way  Please note Array is an object in NET so you need to check for null before

User · Answer

You can use if  array    null    array Length    0   OR if    array    null  amp  amp  array Length    0    NOTE      To insure that c  will implement the short circuit correctly  you have to compare that the object with NULL before you go to the children compare of the object  C  7 0 and above if   array  Length    0

User · Answer

You can absolutely check an empty array s length  However  if you try to do that on a null reference you ll get an exception  I suspect that s what you re running into  You can cope with both though   if  array    null    array Length    0    If that isn t the cause  please give a short but complete program demonstrating the problem  If that was the cause  it s worth taking a moment to make sure you understand null references vs  empty  collections strings whatever

User · Answer

do you mean empty or null  two different things   if the array is instantiated but empty  then length is correct  if it has not been instantiated then test vs null

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Jon Skeet answered correctly  Just remember that the order of the test in the  IF  is important  Check for the null before the length  I also prefer to put the null on the left side of the equal which is a habit I got from Java that made the code more efficient and fast    I don t think it s important in a lot of application today  but it s a good practice    if  null    array    array Length    0

User · Answer

As other have already suggested it is likely you are getting a NullReferenceException which can be avoided by first checking to see if the reference is null  However  you need to ask yourself whether that check is actually warranted  Would you be doing it because the reference really might be null and it being null has a special meaning in your code  Or would you be doing it to cover up a bug  The nature of the question leads me to believe it would be the latter  In which case you really need to examine the code in depth and figure out why that reference did not get initialized properly in the first place

[c#] If (Array.Length == 0)

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