I have to parse a binary file having a number of fixed records, each
record containing datas in fixed positions. I would like to parse
this binary file into an array of structures having members that
represent those fields, so that I can access the records in a
meaningful way.
Using C, I would have defined a struct that I could cast a byte array
into, which held exactly one of these fixed records. The struct would
be defined as such:
struct rec {
char index[1] ;
char padding[50];
char name[28];
};
No big deal, (rec)char_array;.

I tried to do something similar in C#, and I am getting an error
telling me that:
"Array size cannot be specified in a variable declaration"

How might I create a data structure with fixed-size members at design
time?
Do I really have to encapsulate this into a class that contains logic
to parse the record sequentially when it's instantiated?

Thanks.

Hi Robert,

i think, you are looking for this (PInvoke Style):

[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Ansi)
public struct rec
{
[MarshalAs(UnmanagedType.LPStr,SizeConst=1)]
string index; //could also be a byte
[MarshalAs(UnmanagedType.LPStr,SizeConst=50)]
string padding;//could also be a byte
[MarshalAs(UnmanagedType.LPStr,SizeConst=28)]
string name;//could also be a byte
}

then you go like this:

rec your_rec = (rec)
Marshal.PtrToStructure(ptrPointerToYourBytesBlockOfMemory,typeof(rec));
MessageBox.Show(your_rec.name);

Regards

Kerem

--
-----------------------
Beste Grüsse / Best regards / Votre bien devoue
Kerem Gümrükcü
Latest Project: http://www.codeplex.com/restarts
Latest Open-Source Projects: http://entwicklung.junetz.de
-----------------------
"This reply is provided as is, without warranty express or implied."
"robert.waters" <(E-Mail Removed)> schrieb im Newsbeitrag
news:9b88c175-3ba3-4339-8957-(E-Mail Removed)...
>I have to parse a binary file having a number of fixed records, each
> record containing datas in fixed positions. I would like to parse
> this binary file into an array of structures having members that
> represent those fields, so that I can access the records in a
> meaningful way.
> Using C, I would have defined a struct that I could cast a byte array
> into, which held exactly one of these fixed records. The struct would
> be defined as such:
> struct rec {
> char index[1] ;
> char padding[50];
> char name[28];
> };
> No big deal, (rec)char_array;.
>
> I tried to do something similar in C#, and I am getting an error
> telling me that:
> "Array size cannot be specified in a variable declaration"
>
> How might I create a data structure with fixed-size members at design
> time?
> Do I really have to encapsulate this into a class that contains logic
> to parse the record sequentially when it's instantiated?
>
> Thanks.

On Oct 20, 2:10*am, Kerem Gümrükcü <kareem...@hotmail.com> wrote:
> Hi Robert,
>
> i think, you are looking for this (PInvoke Style):
>
> [StructLayout(LayoutKind.Sequential,CharSet=CharSet.Ansi)
> public struct rec
> {
> * * [MarshalAs(UnmanagedType.LPStr,SizeConst=1)]
> * * string index; //could also be a byte
> * * [MarshalAs(UnmanagedType.LPStr,SizeConst=50)]
> * * string padding;//could also be a byte
> * * [MarshalAs(UnmanagedType.LPStr,SizeConst=28)]
> * * string name;//could also be a byte
>
> }
>
> then you go like this:
>
> rec your_rec = (rec)
> Marshal.PtrToStructure(ptrPointerToYourBytesBlockOfMemory,typeof(rec));
> MessageBox.Show(your_rec.name);
>
> Regards
>
> Kerem
>

Thank you, that's exactly what I needed.

On Oct 20, 2:10*am, Kerem Gümrükcü <kareem...@hotmail.com> wrote:
> Hi Robert,
>
> i think, you are looking for this (PInvoke Style):
>
> [StructLayout(LayoutKind.Sequential,CharSet=CharSet.Ansi)
> public struct rec
> {
> * * [MarshalAs(UnmanagedType.LPStr,SizeConst=1)]
> * * string index; //could also be a byte
> * * [MarshalAs(UnmanagedType.LPStr,SizeConst=50)]
> * * string padding;//could also be a byte
> * * [MarshalAs(UnmanagedType.LPStr,SizeConst=28)]
> * * string name;//could also be a byte
>
> }
>
> then you go like this:
>
> rec your_rec = (rec)
> Marshal.PtrToStructure(ptrPointerToYourBytesBlockOfMemory,typeof(rec));
> MessageBox.Show(your_rec.name);
>

I have a problem: I get an 'attempted to read protected memory"
exception.
[StructLayout(LayoutKind.Sequential,CharSet=CharSet.Ansi)]
public struct PbEntry // size=385b
{
[MarshalAs(UnmanagedType.LPStr,SizeConst=1)]
string index;
[MarshalAs(UnmanagedType.LPStr,SizeConst=5)]
string nameHeader;
[MarshalAs(UnmanagedType.LPStr,SizeConst=123)]
string contactName;
[MarshalAs(UnmanagedType.LPStr, SizeConst = 11)]
string numsHeader;
[MarshalAs(UnmanagedType.LPStr, SizeConst = 49)]
string cellNumber;
[MarshalAs(UnmanagedType.LPStr, SizeConst = 49)]
string homeNumber;
[MarshalAs(UnmanagedType.LPStr, SizeConst = 49)]
string workNumber;
[MarshalAs(UnmanagedType.LPStr, SizeConst = 49)]
string otherNumber1;
[MarshalAs(UnmanagedType.LPStr, SizeConst = 49)]
string otherNumber2;
}

...... program and FileStream ('fs') set-up .....

byte[] pbData = new byte[385];
fs.Read(pbData, 0, 385);
// pbData is now populated correctly
PbEntry pb=new PbEntry();
IntPtr ptr = Marshal.AllocHGlobal(pbData.Length);
try
{
Marshal.Copy(pbData, 0, ptr, pbData.Length);
pb = (PbEntry)Marshal.PtrToStructure(ptr,
typeof(PbEntry)); // exception happens here
Console.WriteLine(pb.ToString());
}
finally
{
Marshal.FreeHGlobal(ptr);
}

Any reason why that is protected memory?

Thanks!

On Oct 20, 7:16*pm, "robert.waters" <robert.wat...@gmail.com> wrote:
> On Oct 20, 2:10*am, Kerem Gümrükcü <kareem...@hotmail.com> wrote:
>
>
>
> > Hi Robert,
>
> > i think, you are looking for this (PInvoke Style):
>
> > [StructLayout(LayoutKind.Sequential,CharSet=CharSet.Ansi)
> > public struct rec
> > {
> > * * [MarshalAs(UnmanagedType.LPStr,SizeConst=1)]
> > * * string index; //could also be a byte
> > * * [MarshalAs(UnmanagedType.LPStr,SizeConst=50)]
> > * * string padding;//could also be a byte
> > * * [MarshalAs(UnmanagedType.LPStr,SizeConst=28)]
> > * * string name;//could also be a byte
>
> > }
>
> > then you go like this:
>
> > rec your_rec = (rec)
> > Marshal.PtrToStructure(ptrPointerToYourBytesBlockOfMemory,typeof(rec));
> > MessageBox.Show(your_rec.name);
>
> I have a problem: I get an 'attempted to read protected memory"
> exception.
> * * [StructLayout(LayoutKind.Sequential,CharSet=CharSet.Ansi)]
> * * public struct PbEntry *// size=385b
> * * {
> * * * * [MarshalAs(UnmanagedType.LPStr,SizeConst=1)]
> * * * * string index;
> * * * * [MarshalAs(UnmanagedType.LPStr,SizeConst=5)]
> * * * * string nameHeader;
> * * * * [MarshalAs(UnmanagedType.LPStr,SizeConst=123)]
> * * * * string contactName;
> * * * * [MarshalAs(UnmanagedType.LPStr, SizeConst = 11)]
> * * * * string numsHeader;
> * * * * [MarshalAs(UnmanagedType.LPStr, SizeConst = 49)]
> * * * * string cellNumber;
> * * * * [MarshalAs(UnmanagedType.LPStr, SizeConst = 49)]
> * * * * string homeNumber;
> * * * * [MarshalAs(UnmanagedType.LPStr, SizeConst = 49)]
> * * * * string workNumber;
> * * * * [MarshalAs(UnmanagedType.LPStr, SizeConst = 49)]
> * * * * string otherNumber1;
> * * * * [MarshalAs(UnmanagedType.LPStr, SizeConst = 49)]
> * * * * string otherNumber2;
> * * *}
>
> ..... program and FileStream ('fs') set-up .....
>
> * * * * * * * * byte[] pbData = new byte[385];
> * * * * * * * * fs.Read(pbData, 0, 385);
> * * * * * * * * // pbData is now populated correctly
> * * * * * * * * PbEntry pb=new PbEntry();
> * * * * * * * * IntPtr ptr = Marshal.AllocHGlobal(pbData.Length);
> * * * * * * * * try
> * * * * * * * * {
> * * * * * * * * * * Marshal.Copy(pbData, 0, ptr, pbData.Length);
> * * * * * * * * * * pb = (PbEntry)Marshal.PtrToStructure(ptr,
> typeof(PbEntry)); // exception happens here
> * * * * * * * * * * Console.WriteLine(pb.ToString());
> * * * * * * * * }
> * * * * * * * * finally
> * * * * * * * * {
> * * * * * * * * * * Marshal.FreeHGlobal(ptr);
> * * * * * * * * }
>
> Any reason why that is protected memory?
>
> Thanks!

Replacing UnmanagedType.LPStr with UnmanagedType.ByValTStr for each
struct member fixed this problem.
Does anyone have any idea why?
Note: the data inside the records had many nulls (\0), which I figured
wouldn't be a problem because they typically follow strings of non-
null characters, and so would fit the model of 'null-terminated ANSI
character string'.
Thank you for any input that would help.