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   ► KBProgrammingDelphi Prism   Print This     
  From the November 2015 Issue of Prestwood eMag
Delphi Prism Empty String Check (length)
Posted 10 years ago on 9/16/2009
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Languages Focus: Empty String Check

An empty string is a zero length string, a string that is equal to null (""), or not assigned. In some languages, you can check if a string is empty by comparing it to an empty string (""). Some languages distinguish between nil and null ("") so checking if the length is 0 is easier.

Delphi Prism Empty String Check

In Prism, a string can be nil (unassigned), assigned an empty string (""), or assigned a value.  Therefore, to check if a string is empty, you have to check against both nil and (""). Alternatively, you can check the length of the string or use String.IsNullOrEmpty.

Syntax Example:
var s: String; 
if (s = nil) or (s = '') then
  MessageBox.Show("empty string");

or use length:

if length(s) = 0 then
  MessageBox.Show("empty string");

Using IsNullOrEmpty

The .NET framework provides a IsNullOrEmpty static method as part of the String class. Remember, the syntax to use a static method is always ClassName.MethodName and you do not have to create the class ahead of time because it is static.

var s: String;
//Unassigned check.
If String.IsNullOrEmpty(s) then
MessageBox.Show("empty or null string");
//Assigned a non-zero value.
s := "health care reform";
If Not String.IsNullOrEmpty(s) then
MessageBox.Show("string contains a non zero value");
//Empty string.
s := "";
If String.IsNullOrEmpty(s) then
MessageBox.Show("empty or null string");

More Info


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