Frequently used string manipulation

Quick examples for MID LEFT and RIGHT string functions using INSTR FIND and LEN.

How do you find the text between two search terms (Say: after a colon and before a comma)? How do you get the remainder of a word (using MID or using RIGHT)? Which of these functions use Zero-based params and return codes vs One-based? What happens when things go wrong? How do they handle empty strings, unfound results and negative numbers?

String manipulation frequently used examples

Better MID() and other string extraction examples, currently lacking from the web. Please help me make a good example, or complete this one here. Something like this:

DIM strEmpty as String, strNull as String, theText as String
DIM idx as Integer
DIM letterCount as Integer
DIM result as String

strNull = NOTHING
strEmpty = ""
theText = "1234, 78910"

' -----------------
' Extract the word after the comma ", "  and before "910"  result: "78" ***
' -----------------

' Get index (place) of comma using INSTR
idx = ...   ' some explanation here
if idx < ... ' check if no comma found in text

' or get index of comma using FIND
idx = ...   ' some explanation here... Note: The difference is...
if idx < ...  ' check if no comma found in text

result = MID(theText, ..., LEN(...

' Retrieve remaining word after the comma
result = MID(theText, idx+1, LEN(theText) - idx+1)

' Get word until the comma using LEFT
result = LEFT(theText, idx - 1)

' Get remaining text after the comma-and-space using RIGHT
result = ...

' What happens when things go wrong
result = MID(strNothing, 1, 2)    ' this causes ...
result = MID(strEmpty, 1, 2) ' which causes...
result = MID(theText, 30, 2) ' and now...
result = MID(theText, 2, 999) ' no worries...
result = MID(theText, 0, 2)
result = MID(theText, 2, 0)
result = MID(theText -1, 2)
result = MID(theText 2, -1)
idx = INSTR(strNothing, "123")
idx = INSTR(theText, strNothing)
idx = INSTR(theText, strEmpty)
i = LEN(strEmpty)
i = LEN(strNothing) '...

Please feel free to edit this example and make it better. As long as it remains clear, and has in it common usage practices.