Extract substring

Author: Dave
Date: 08.05.19 - 11:36pm

One of the most common tasks you will encounter is the need to extract a string fragment from a larger block.

Its a very simple repetitive task and I generally have just done it inline for many many years. The catch is it does require several tests along the way to make sure it is done safely without error on unexpected input.

Years ago I wrote a StringEx class that handled many things including an extract function, yet I rarely use it since it seems to bulky unless I am really doing some heavy duty string parsing.

I finally got tired and just pulled out the extract routine into its own standalone function for general use. Makes extractions nice safe one liners.

Couple notes I left most args variants for flexibility. marker1 or marker2 can be empty and it will use defaults. I decided to return the extracted string length instead of a simple boolean because its a little bit richer feedback that could be useful (if you were expecting a string of min length in return), just remember to test =0 or > 0 instead of the easier if extract() then or if not. Easy to change to your liking.

The output of the below function is s1 = 's1'; m2 = m2

Private Sub Form_Load()
    Dim m2, s1, pos
    Const base = "test <m1> 's1' <m2>"
    If Extract(base, "'", "'", s1, True, , pos) > 0 Then
        Debug.Print "s1 = " & s1
    End If
    If Extract(base, "<", ">", m2, , pos) > 0 Then
        Debug.Print "m2 = " & m2
    End If
End Sub

Function Extract(value, marker1, marker2, ByRef outVar, _
                Optional includeMarkers As Boolean = False, _
                Optional Start = 1, _
                Optional ByRef lastPos, _
                Optional method As VbCompareMethod = vbBinaryCompare _
) As Long

    Dim a As Long, b As Long
    lastPos = 0
    outVar = Empty
    If Len(marker1) = 0 Then
        a = 1
        a = InStr(Start, value, marker1, method)
        If a < 1 Then Exit Function
    End If
    a = a + Len(marker1)
    If Len(marker2) = 0 Then
        outVar = Mid(value, a)
        b = InStr(a, value, marker2, method)
        If b < 1 Then Exit Function
        lastPos = b + Len(marker2)
        outVar = Mid(value, a, b - a)
    End If
    If includeMarkers Then outVar = marker1 & outVar & marker2
    Extract = Len(outVar)
End Function

Comments: (0)

Leave Comment:
Email: (not shown)
Message: (Required)
Math Question: 71 + 17 = ? followed by the letter: X 

About Me
More Blogs
Main Site
Console tricks
FireFox temp dir
OCX License
Extract substring
VB6 Console Apps
VB6 Debugger View As Hex tooltips
VB6 - C Share registry data
VB6 Addin Missing Menus
VB6 Class Init Params
VB6 isIn function
Python and VB6
Python pros and cons
download web Dir
vc rand in python
VB6 Language Enhancement
Register .NET as COM
UDT Tricks pt2
Remote Data Extraction
Collection Extender
VB6 FindResource
DirList Single Click
Reset CheckPoint VPN Policy
VB6 BSTR Oddities Explained
SafeArrays in C
BSTR and Variant in C++
Property let optional args
Misc Libs
Enum Named Pipes
Vb6 Collection in C++
VB6 Overloaded Methods
VB6 Syncronous Socket
Simple IPC
VB6 Auto Resize Form Elements
Mach3 Automation
Exit For in While
C# self register ocx
VB6 Class Method Pointers
JS Debugger
Duktape Debug Protocol
QtScript 4 VB
Vb6 Named Args
vb6 Addin Part 2
VB6 Addin vrs Toolbars
OpenFile Dialog MultiSelect
Duktape Example
DukTape JS
VB6 Unsigned
.Net version
TitleBar Height
.NET again
VB6 Self Register OCXs
Query Last 12 Mos
Progid from Interface ID
VB6 to C Array Examples
Human Readable Variant Type
ScriptBasic COM Integration
CodeView Addin
ScriptBasic - Part 2
Script Env
printf override
History Combo
Disable IE
API Hooking in VB6
Addin Hook Events
FastBuild Addin
VB6 MemoryWindow
Link C Obj Files into VB6
Vb6 Standard Dlls
CStr for Pascal
Lazarus Review
asprintf for VS
VB6 GlobalMultiUse
Scintilla in VB6
Dynamic Highlight
WinVerifyTrust, CryptMsgGetParam VB6
MS GLEE Graphing
printf for VB6
C# App Config
Tero DES C# Test
VC 2008 Bit Fields
Speed trap
C# Db Class Generator
VB6 vrs .NET (again)
FireFox Whois Extension
git and vb6
Code Additions
Compiled date to string
C# ListView Sorter
VB6 Wish List
C# Process Injection
C# PE Offset Calculator
VB6 Async Download
Show Desktop
coding philosophy
Code release
Dll Not Found in IDE
Advanced MSScript Control
random tip
Clipart / Vector Art
VB6 Callback from C#
Binary data from VB6 to C#
CSharp and MsScriptControl
HexDumper functions
Js Beautify From VB6 or C#
vb6 FormPos
Inline Asm w VB6
The .NET Fiasco
One rub on computers
Universal extractor