GAMBAS BOOK 3.19.5

For operations with strings, Gambas provides you with only 2 operators. For the comparisons of two strings, you will mainly use the comparison operators in table 8.3.2.1.

Gambas knows the following operators for operands of type string:

Table 8.3.1.1: String operators

Message.Error("Fehler: " & Chr(10) & "The character is not in the input alphabet!")
If NOT Exist(User.Home &/ "V24T" &/ "v24T.conf") Then …
Path = SettingsP.DefaultDir &/ Application.Name & ".conf"

Note that in the third example, the last & links two strings to a complete filename (file name and extension such as udpserver.conf).

Of the comparison operators in the following table, the last three are of particular interest because they can be used effectively in many cases by specifying patterns.

Table 8.3.2.1: Comparison operators 1 for strings

[1] Dim sCharacterstring As String
[2]
[3] sCharacterstring = "Gambas"
[4]
[5] Message.Info(IIF(sCharacterstring = "gambas", "Comparison true.", "Comparison false."))
[6] Message.Info(IIF(sCharacterstring == "gaMBas", "Comparison true.", "Comparison false."))

Comments:

• The equals sign in line 1 is an assignment operator.
• In the first comparison IF sCharacterstring = “gambas” in the 5th line, the equal sign is used as a comparison operator. The comparison provides a false statement.
• In the 6th line, the comparison IF sCharacterstring == “gaMBas” delivers a true statement, because the comparison does NOT take capital and small letters into account.

Table 8.3.2.2: Comparison operators for strings

For example, the comparison operators ⇐ and >= are available in the class app/src/gambas3/.src/Component/CSymbolInfo.class and are used there to determine whether a single character stored in the string sCar belongs to a certain interval A to Z in the ASCII character set.

If (sCar >= "A" AND sCar <= "Z") OR sCar = "." Then ...

For example, if you want to sort character strings with your own procedures, you can use the above-mentioned comparison operators for character strings, as you can see from the following source code:

Public Sub Form_Open()
  FMain.Center
  FMain.Resizable = False
End ' Form_Open()
 
Public Sub btnSort_Click()
  Dim aStringArray As String[]
 
  aStringArray = Split(txaText.Text, "\n")
    SwapSortStrings(aStringArray)
  txaText.Text = aStringArray.Join("\n")
 
End ' btnSort_Click()
 
Private Sub SwapSortStrings(aMatrix As String[])
' Implementation SwapSort algorithm: http://de.wikipedia.org/wiki/Swap-Sort
  Dim i, j, m As Integer
  Dim sTemp As String
 
  i = 0
  While i < aMatrix.Count
    m = 0
    For j = 0 To aMatrix.Count - 1
      If aMatrix[j] < aMatrix[i] Then Inc m ' Comparison of strings
    Next ' j
    If i = m Then
       Inc i
    Else
       sTemp = aMatrix[m]
       aMatrix[m] = aMatrix[i]
       aMatrix[i] = sTemp
    Endif ' i = m?
  Wend
End

Figures 8.3.2.1 and 8.3.2.2: Sorting strings

A disadvantage of SwapSort: Each item in the list to be sorted may only appear once. The method String[].Sort() does not have this disadvantage and uses the QuickSort algorithm.

bResult = String [NOT] LIKE Pattern

The boolean variable bResult gets the value TRUE if the pattern string matches string. If NOT is used, the test is inverted.

The operator is not case-sensitive and the following patterns can be used:

Table 8.3.3.3.1: Sample

Table 8.3.3.3.2: Comparison operators 1 for strings

Please note: LIKE is only valid for ASCII strings. If you are testing against UTF-8 strings, you must use the gb.pcre component.

bResult = String [NOT] BEGINS Pattern

The boolean variable bResult gets the value TRUE when string begins with the pattern string. If NOT is used, the test is inverted. The BEGINS operator is case-sensitive.

Table 8.3.4.1: Examples for the BEGINS operator

bResult = String [NOT] ENDS Pattern

The boolean variable bResult receives the value TRUE if string ends with the pattern string. If NOT is used, the test is inverted. The ENDS operator is case-sensitive.

Table 8.3.5.1: Examples for the operator ENDS