Prestwood IT: Empty String Check (Cross Reference Coding Encyclopedia: Delphi Prism)

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► KB ► To/From Guides ► Delphi Prism

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Empty String Check

Languages Focus

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: length

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");

Delphi Prism Empty String Check (length)

Cross Reference Examples:

Access VBA: Len(s&vbNullString)

In Access VBA, you have to add an empty string to the value being compared in order to get consistent results. For example, add &"" to your string varilable or it's code equivalent &vbNullString. Then compare to an empty string or verify it's length to 0 with Len.

Syntax Example:

All these will work for variables unassigned, set to "", or set to Null:

If s&"" = "" Then
  MsgBox ("Quotes with &'' say null is empty")
End If

 
If Len(s&"") = 0 Then
  MsgBox ("Len with &'' says null is empty")
End If

If Len(s&vbNullString) = 0 Then
  MsgBox ("Using vbNullString also works!")
End If

ASP Classic: Len(s&vbNullString)

In ASP Classic, you have to add an empty string to the value being compared in order to get consistent results. For example, add &"" to your string varilable or it's code equivalent &vbNullString. Then compare to an empty string or verify it's length to 0 with Len.

Syntax Example:

All these will work for variables unassigned, set to "", or set to Null:

If s&"" = "" Then
  Response.Write("<br>Quotes with &'' say null is empty")
End If

 
If Len(s&"") = 0 Then
  Response.Write("<br>Len with &'' says null is empty")
End If

If Len(s&vbNullString) = 0 Then
  Response.Write("<br>Using vbNullString also works!")
End If

ASP Classic Empty String Check (Len(s&vbNullString)) 1 certification question.

C#: String.IsNullOrEmpty

The .Net framework offers a static method in the string class: String.IsNullOrEmpty.

Syntax Example:

String s;

s = "";
//s = null;  //Uncomment to test 2nd case.

if (String.IsNullOrEmpty(s))
{
  MessageBox.Show("empty string");
}

C++/CLI: String.IsNullOrEmpty

The .Net framework offers a static method in the string class: String.IsNullOrEmpty.

Syntax Example:

String^ s;

//s = ""; //Uncomment to test 2nd case.

if (String::IsNullOrEmpty(s))
{
  MessageBox::Show("empty string");
}

Corel Paradox: isBlank() or not isAssigned()

In ObjectPAL, an empty variable can be unassigned (essentially null) or blank (equivalent to ""). You have to use both isBlank and isAssigned to check for an empty string.

Syntax Example:

var
 s String
endVar

;s = ""  ;Uncomment to test 2nd case.

if isBlank(s) or not isAssigned(s) Then
 msgInfo("", "empty string")
endIf

ObjectPAL Empty String Check (isBlank() or not isAssigned())

Delphi: length(s) = 0

Length() or SizeOf() will correctly identify an unassigned string variable or an empty string.

Syntax Example:

if length(s) = 0 then
  ShowMessage('empty string');

Java: IsEmpty

VB Classic: Len(s&vbNullString)

In VB Classic, you have to add an empty string to the value being compared in order to get consistent results. For example, add &"" to your string varilable or it's code equivalent &vbNullString. Then compare to an empty string or verify it's length to 0 with Len.

Syntax Example:

All these will work for variables unassigned, set to "", or set to Null:

If s&"" = "" Then
  MsgBox ("Quotes with &'' say null is empty")
End If

 
If Len(s&"") = 0 Then
  MsgBox ("Len with &'' says null is empty")
End If

If Len(s&vbNullString) = 0 Then
  MsgBox ("Using vbNullString also works!")
End If

VB.Net: String.IsNullOrEmpty

In .Net, a string can be null or empty. The .Net framework offers a static method in the string class: String.IsNullOrEmpty to check if a string is null or empty.

Syntax Example: 1 certification question.

Dim s As String

's = "" 'Uncomment to test 2nd case.

If String.IsNullOrEmpty(s) Then
  MessageBox.Show("hello")
End If