The difference between + and & for joining strings in VB.NET
None.
As you can see below. These two lines of code compiles exactly to the same CIL code:
Module Module1
Sub Main()
Dim s1 As String = "s1"
Dim s2 As String = "s2"
s2 += s1
s1 &= s2
End Sub
End Module
Compiles to (note System.String::Concat
):
.method public static void Main() cil managed
{
.entrypoint
.custom instance void [mscorlib]System.STAThreadAttribute::.ctor() = ( 01 00 00 00 )
// Code size 31 (0x1f)
.maxstack 2
.locals init ([0] string s1,
[1] string s2)
IL_0000: nop
IL_0001: ldstr "s1"
IL_0006: stloc.0
IL_0007: ldstr "s2"
IL_000c: stloc.1
IL_000d: ldloc.1
IL_000e: ldloc.0
IL_000f: call string [mscorlib]System.String::Concat(string,
string)
IL_0014: stloc.1
IL_0015: ldloc.0
IL_0016: ldloc.1
IL_0017: call string [mscorlib]System.String::Concat(string,
string)
IL_001c: stloc.0
IL_001d: nop
IL_001e: ret
} // end of method Module1::Main
The & operator always makes sure that both operands are strings, while the + operator finds the overload that matches the operands.
The expression 1 & 2
gives the value "12", while the expression 1 + 2 gives the value 3.
If both operands are strings, there is no difference in the result.
There's no difference if both operands are strings. However, if one operand is a string, and one is a number, then you run into problems, see the code below.
"abc" + "def" = "abcdef"
"abc" & "def" = "abcdef"
"111" + "222" = "111222"
"111" & "222" = "111222"
"111" & 222 = "111222"
"111" + 222 = 333
"abc" + 222 = conversion error
Therefore I recommend to always use &
when you mean to concatenate, because you might be trying to concatenate an integer, float, decimal to a string, which will cause an exception, or at best, not do what you probably want it to do.
The + operator can be either addition or concatenation. The & is only concatenation. If the expressions are both strings the results would be the same.
I use & when working with strings, and + when working with numbers, so there is never confusion about my intent. If you mistakenly use + and one expression is a string and one is a number, you run the risk of un-desired results.