+和&之间的区别,用于在VB.NET中连接字符串

Question

是什么区别+,并&在VB.NET加入字符串？

Answer 1

如果两个操作数都是字符串,则没有区别.但是,如果一个操作数是一个字符串,而一个是数字,那么您遇到问题,请参阅下面的代码.

"abc" + "def" = "abcdef"
"abc" & "def" = "abcdef"
"111" + "222" = "111222"
"111" & "222" = "111222"
"111" & 222 = "111222"
"111" + 222 = 333
"abc" + 222 = conversion error

因此,我建议在&连接时始终使用,因为您可能尝试将整数,浮点数,十进制连接到字符串,这将导致异常,或者充其量,不执行您可能希望它执行的操作.

Answer 2

&运算符总是确保两个操作数都是字符串,而+运算符找到与操作数匹配的重载.

表达式1 & 2给出值"12",而表达式1 + 2给出值3.

如果两个操作数都是字符串,则结果没有区别.

Answer 3

没有.

如下所示.这两行代码完全编译为相同的IL代码:

Module Module1

    Sub Main()
        Dim s1 As String = "s1"
        Dim s2 As String = "s2"
        s2 += s1
        s1 &= s2
    End Sub

End Module

编译成(注释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