主题：[讨论]用copymemory拷贝含有String的Type时的问题
天天学习
[专家分：4570] 发布于 2010-03-31 10:47:00
在一个类模块中的一函数中需要传递/返回一个自定义的类型，但是写成如下格式的函数时编译报错
public function GetAddInfo(byval index as integer) as AddInfo
'....
end function
public function SetAddInfo(byval index as integer,byval typAdd as AddInfo) as long
'....
end function
“只有在公共对象模块中定义的公共用户定义类型可以作为参数、类模块的公共过程返回类型、公共用户定义类型的字段使用。”
即使把参数/返回类型改成variant，也不行。
“只有在公共对象模块中定义的用户定义类型才可以与变体类型强制转换或传递给后期绑定的函数”
于是想到用copymemory。
[code=c]
在标准模块中，
Public Type AddInfo
AddName As Long 'As String*255 时不正常
AddBZ As Long
AddRate As Single
End Type
在类模块中，
Private m_add(2) As AddInfo
Public Function GetAddInfo(ByVal Index As Integer) As Long
Debug.Assert Index >= 0 And Index <= 2
CopyMemory GetAddInfo, VarPtr(m_add(Index)), 4
Debug.Print GetAddInfo, VarPtr(m_add(Index))
End Function
Public Function SetAddInfo(ByVal Index As Integer, ByVal pTypAdd As Long) As Long
Debug.Assert Index >= 0 And Index <= 2
CopyMemory m_add(Index), ByVal pTypAdd, Len(m_add(Index))
Debug.Print m_add(Index).AddName, m_add(Index).AddBZ, m_add(Index).AddRate, VarPtr(m_add(Index))
End Function
然后，在窗体中,
Private Sub Command1_Click()
Dim a As AddInfo
a.AddName = 213 '"test"
a.AddBZ = 89
a.AddRate = 45.45
Dim c As Class1
Set c = New Class1
Call c.SetAddInfo(0, ByVal VarPtr(a))
Dim b As AddInfo
Dim p As Long
p = c.GetAddInfo(0)
CopyMemory b, ByVal p, Len(b)
Debug.Print b.AddName, b.AddBZ, b.AddRate
End Sub
'[color=red]当结构体的AddName为String类型时，取不到后面两个成员的值[/color]
[/code]
[size=4][color=red]PS.帖子还没发出去时，突然想到干脆不指定String的长度试试，结果。。。正常。-.-||[/color][/size]
最后更新于：2010-03-31 10:50:00
回复列表 （共9个回复）
沙发
guoyong_cy [专家分：3050] 发布于 2010-04-18 20:01:00
因为255 mod 4<>0 ,没有内存对齐,所以就错了!
而单纯用String,不指定长度,实际存储的只是String的地址,长度是4,后面对齐了,后面的值正常,但你无法直接用COPYMEMORY复制STRING.
因为类模块里面不能返回公共的定长字符串,我一般是这样定义的:
type typeX
lenStr as long '字符串的实际长度
nB(0 to nn) as byte 'nn是4X-1,用来存字符串
...
end type
这个类型相当于重新定义了String类型,但长度是固定的,而且可以直接用COPYMEMORY 复制,只是还需要写个函数把这个数组转换成字符串
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9 楼
孙瑞 [专家分：590] 发布于 2011-05-10 14:10:00
能不能简单讲一下什么是内存对齐？我好像听到过几次了。
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