How to check if a dynamic array is empty

Question

I have a procedure declared like this:

procedure MyProc(List: Array of string); 

I want to know how to check if the List parameter is empty.

For example:

 procedure MyProc(List: Array of string); begin if List=[] then // here I want to check if the List array is empty //do something else //do something else end; 

How can i do this?

Answer 1

you can use the Length function

 procedure MyProc(List: Array of string); begin if Length(List)=0 then // is empty ? //do something else // do something else end; 

Answer 2

Empty arrays are nil :

 if List = nil then // it empty 

(This also means that SetLength(List, 0) and List := nil are equivalent commands.)

Empty arrays have the last index, which is less than the first index, which for the open array in your example means the presence of a negative last index:

 if High(List) < 0 then // it empty 

This means that if you want to avoid starting a loop in an empty array, you do not need to do anything special. Just write the loop as usual:

 for i := Low(List) to High(List) do // won't run if List is empty 

Answer 3

Personally, I always write

 if Assigned(List) then 

but not

 if List<>nil then 

because I believe that it reads better, and not just for dynamic arrays.

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Answers the question about dynamic arrays, but your example is an open array, so there are two possible questions here.

For open arrays, I would use Length() or high() to make a decision based on the size of the array. I would not be tempted by the arguments that Pointer(List)<>nil faster than Length(List)<>nil . The difference in speed between these parameters will not be distinguishable, so you should use the most understandable and understandable option.