VB.NET String Between, Before and After Functions

Use functions to get strings between, before and after other strings. Call IndexOf and LastIndexOf.

Between, before, after. A string contains the syntax of a simple language. It has characters between, before and after other strings.

With special functions, we can extract these substrings. Functions like Between, Before and After get substrings based on the surrounding text. This helps parse a simple language.Substring

An example program. This module has implementations for the Between, Before and After string functions. These functions take substrings based on adjacent substrings.

Between: This uses IndexOf and LastIndexOf to locate the positions of the two specified strings. It returns the substring in between.

IndexOf LastIndexOf

Before: This calls IndexOf to find the argument string. Then it returns the characters before that string's location.

After: This finds the last occurrence of the argument string with LastIndexOf. It then returns the substring before that point.

VB.NET program that uses Between, Before, After on Strings Module Module1 Function Between(value As String, a As String, b As String) As String ' Get positions for both string arguments. Dim posA As Integer = value.IndexOf(a) Dim posB As Integer = value.LastIndexOf(b) If posA = -1 Then Return "" End If If posB = -1 Then Return "" End If Dim adjustedPosA As Integer = posA + a.Length If adjustedPosA >= posB Then Return "" End If ' Get the substring between the two positions. Return value.Substring(adjustedPosA, posB - adjustedPosA) End Function Function Before(value As String, a As String) As String ' Get index of argument and return substring up to that point. Dim posA As Integer = value.IndexOf(a) If posA = -1 Then Return "" End If Return value.Substring(0, posA) End Function Function After(value As String, a As String) As String ' Get index of argument and return substring after its position. Dim posA As Integer = value.LastIndexOf(a) If posA = -1 Then Return "" End If Dim adjustedPosA As Integer = posA + a.Length If adjustedPosA >= value.Length Then Return "" End If Return value.Substring(adjustedPosA) End Function Sub Main() Dim test As String = "DEFINE:A=TWO" ' Test the Between Function. Console.WriteLine(Between(test, "DEFINE:", "=")) Console.WriteLine(Between(test, ":", "=")) ' Test the Before Function. Console.WriteLine(Before(test, ":")) Console.WriteLine(Before(test, "=")) ' Test the After Function. Console.WriteLine(After(test, ":")) Console.WriteLine(After(test, "DEFINE:")) Console.WriteLine(After(test, "=")) End Sub End Module Output A A DEFINE DEFINE:A A=TWO A=TWO TWO

In Main, we parse a simple example string. We use a simple language syntax that could be used to define variables. We parse this string with Between, Before and After.

Tip: A Dictionary could be used to store the key and value pairs returned by the parsing method.

Dictionary

For good performance, avoiding substrings and IndexOf calls is beneficial. If in your code the above functions cause extra work, adding more custom methods is worth consideration.

A review. Sometimes it is helpful to create functions that extract parts of strings. Substring() could be used directly. But this could become complicated and prone to errors.