问题
I'm maintaining an application written in Microsoft Access with VBA.
I'm glancing over my code and have just noticed I have subconsciously been concatenating strings together with the plus (+) symbol instead of the ampersand. It's been a few years since I've coded in VB6. Could this cause any issues?
Everything seems fine and it will only take a few minutes to fix, I'm just curious as to whether I'm technically doing anything wrong.
回答1:
The ampersand is explicitly a string operation, while the plus is overloaded:
Dim num1 As Integer
num1 = RandomNumberBetween(1, 9)
Dim num2 As Integer
num2 = RandomNumberBetween(1, 9)
Dim randomAge As String 'trying to get a random age between 11 and 99
' works
randomDate = "Your age is " & num1 & num2
'broken
randomDate = "Your age is " + num1 + num2
When used with numbers the plus sign will add.
回答2:
Some examples, from the VBA immediate window (the difference between the third and fourth is particularly vexing):
Print "5" & 6
56
Print 5 & 6
56
Print "5" + 6
11
Print "5" + "6"
56
Print "Five" & 6
Five6
Print "Five" + 6 'Type mismatch
Print "5" & Null
5
Print "5" + Null
Null
回答3:
This can cause issues.
If you use the plus or ampersand to concatenate string values the results are identical
If you use a plus to concatenate a string with a non string value it will throw an error
If you use an ampersand sign vba will try to 'stringify' the values before concatenating.
So string_value + int_value + date_value will error and string_value & int_value & date_value works fine
来源：https://stackoverflow.com/questions/7743823/concatenating-strings-in-vba