Re: passing an struct from vb to c dll

From:

"Jim Langston" <tazmaster@rocketmail.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 12 Jul 2006 04:03:52 -0700

Message-ID:

<3H4tg.1202$cv.142@fe05.lga>

"abhijeet" <abhi.10dulkar@gmail.com> wrote in message
news:1152610698.115573.32370@m79g2000cwm.googlegroups.com...

Hi,
I am having some problem for getting values in struct from the c dll.

I have following definition

Type MBRINFO
szMember As String * 80 ' member name array
usLevel As Integer
End Type

I am passing this struct to c dll for getting back the values filled
from the dll

Declare Function GetMemberInfo Lib "xyz" (pInfo As MBRINFO) As Long

On c side I have code as following

struct MBRINFO
{
char szMember[80];
int usLevel;
}
long GetMemberInfo(MBRINFO * info)
{
long sts = 0;
memset(info,0,sizeof(MBRINFO ));
szMember(info->szMember,"Something");
info->usLevel = 10;
return sts;
}

The definition is exported from the xyz.dll for acess.
But, when I get value back on vb side, I noticed the value for szMember
is filled with assigned value which is "Something" folloed by lot of
space characters. Can somebody help me figure out how to avoid this
issue.

Thanks,
Abhijeet

I believe your problem may do with the C style .vs. Pascal style strings. I
may be wrong, however, but perhaps vb is using the pascal style string where
the first byte is the length of the string, then the contents of the string,
where a C style string is simply null terminated.

To fix this, you should perhaps simply also add the length of the string to
the structure so you can clean it up on the Basic side. Otherwise you'll
need to research what VB is expecting it's string array to be filled with.