Arrays in structures

[Peter Seaman]

I understand that structures are value types and arrays and classes are
reference types. But what about arrays as members of structures i.e. as in
C

struct x
{
int n;
int a[100];
}

How is such a structure (e.g. declared in C++ as a field in a class)
accessed in C#?

Peter Seaman

[Jon Skeet [C# MVP]]

<"Peter Seaman" <Peter MS Seaman at StableSoftware. com>> wrote:

I understand that structures are value types and arrays and classes are
reference types. But what about arrays as members of structures i.e. as in
C

struct x
{
int n;
int a[100];
}

How is such a structure (e.g. declared in C++ as a field in a class)
accessed in C#?

You can't declare it like that in C# - you'd have to declare it as just

int[] a;

and initialise it in a constructor or similar. The struct itself is
still a value type, but the variable a would contain a reference. It's
exactly the same as if you have a struct containing a string reference
or similar.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Gawelek]

> and initialise it in a constructor or similar. The struct itself is

still a value type, but the variable a would contain a reference. It's
exactly the same as if you have a struct containing a string reference
or similar.

Value types live only on stack, but what with struct containing String
variable?
What will happen with this String when for example we leave function ?
Gawel

[Jon Skeet [C# MVP]]

Gawelek <ga*****@NOSPAM EKpoczta.gazeta .pl> wrote:

and initialise it in a constructor or similar. The struct itself is
still a value type, but the variable a would contain a reference. It's
exactly the same as if you have a struct containing a string reference
or similar.
Value types live only on stack

No they don't. See
http://www.pobox.com/~skeet/csharp/memory.html
but what with struct containing String variable?
What will happen with this String when for example we leave function ?

It's the same as always: if there are no live references to the string,
it will eventually be garbage collected.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Gawelek]

> http://www.pobox.com/~skeet/csharp/memory.html

Thanks, now all is clear.

Gawel

[Peter Seaman]

Thanks, so structures containing directly embedded arrays are not possible
in C#. Such structures are possible in other languages such as C++ and I
often use them. What I am still uncertain about is this: if in C++ such a
structure is made a member of a class, can that member be accessed in C# and
if so how?

Peter Seaman

[Jon Skeet [C# MVP]]

<"Peter Seaman" <Peter MS Seaman at StableSoftware. com>> wrote:

Thanks, so structures containing directly embedded arrays are not possible
in C#.
Not as far as I know, no.
Such structures are possible in other languages such as C++ and I
often use them. What I am still uncertain about is this: if in C++ such a
structure is made a member of a class, can that member be accessed in C# and
if so how?

Well, the first thing to do is test whether it is still possible in
*managed* C++ - and then run ildasm on the created assembly and see
what's in it.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Peter Seaman]

> Well, the first thing to do is test whether it is still possible in

*managed* C++ - and then run ildasm on the created assembly and see
what's in it.

No doubt this is good advice but unfortunately I only have C# Standard.
Though this product does contain Visual Studio 2003 and compilers for
JScript .NET and VB .NET, it does not allow me to compile C++ .NET as far as
I can see.

It seems to me that arrays and structures and combinations of such
aggregates are pretty fundamental to programming, so on the face of this
inability for structures to contain embedded arrays is a severe restriction.
Is there an easy way round it? How does C# cope with the many such
structures in the WIN32 API e.g. LPWIN32_FIND_DA TA?

Peter Seaman

[Jon Skeet [C# MVP]]

<"Peter Seaman" <Peter MS Seaman at StableSoftware. com>> wrote:

Well, the first thing to do is test whether it is still possible in
*managed* C++ - and then run ildasm on the created assembly and see
what's in it.
No doubt this is good advice but unfortunately I only have C# Standard.
Though this product does contain Visual Studio 2003 and compilers for
JScript .NET and VB .NET, it does not allow me to compile C++ .NET as far as
I can see.

Ah. I'm afraid I don't know much managed C++ at all - perhaps another
poster with more experience of it could help us?
It seems to me that arrays and structures and combinations of such
aggregates are pretty fundamental to programming, so on the face of this
inability for structures to contain embedded arrays is a severe restriction.
Is there an easy way round it? How does C# cope with the many such
structures in the WIN32 API e.g. LPWIN32_FIND_DA TA?

No idea, I'm afraid :(

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Willy Denoyette [MVP]]

"Peter Seaman" <Peter MS Seaman at StableSoftware. com> wrote in message
news:uI******** *****@TK2MSFTNG P11.phx.gbl...

Well, the first thing to do is test whether it is still possible in
*managed* C++ - and then run ildasm on the created assembly and see
what's in it.

No doubt this is good advice but unfortunately I only have C# Standard.
Though this product does contain Visual Studio 2003 and compilers for
JScript .NET and VB .NET, it does not allow me to compile C++ .NET as far
as
I can see.

It seems to me that arrays and structures and combinations of such
aggregates are pretty fundamental to programming, so on the face of this
inability for structures to contain embedded arrays is a severe
restriction.
Is there an easy way round it? How does C# cope with the many such
structures in the WIN32 API e.g. LPWIN32_FIND_DA TA?

Peter Seaman

This is not such a problem in C#, following is a sample using FindNexttFile
and WIN32_FIND_DATA .

using System;
using System.Runtime. InteropServices ;
namespace Willys
{

[StructLayout(La youtKind.Sequen tial, CharSet = CharSet.Unicode )]
public struct _WIN32_FIND_DAT AW
{
public uint dwFileAttribute s;
public FILETIME ftCreationTime;
public FILETIME ftLastAccessTim e;
public FILETIME ftLastWriteTime ;
public uint nFileSizeHigh;
public uint nFileSizeLow;
public uint dwReserved0;
public uint dwReserved1;
// TCHAR array 260 (MAX_PATH) entries, 520 bytes in unicode
[MarshalAs(Unman agedType.ByValT Str, SizeConst=520)]
public string cFileName;
// TCHAR array 14 TCHAR's alternate filename 28 byes in unicode
[MarshalAs(Unman agedType.ByValT Str, SizeConst=28)]
public string cAlternateFileN ame;
}

[StructLayout(La youtKind.Sequen tial)]
public struct FILETIME
{
public uint dwLowDateTime;
public uint dwHighDateTime;
}
class Tester
{
[DllImport("kern el32.dll", EntryPoint="Fin dFirstFileW", SetLastError=tr ue,
CharSet = CharSet.Unicode )]
public static extern IntPtr FindFirstFileW( string lpFileName, ref
_WIN32_FIND_DAT AW lpFindFileData) ;
static void Main()
{
string file = "*.exe";
_WIN32_FIND_DAT AW fndData = new _WIN32_FIND_DAT AW();
IntPtr hFile = FindFirstFileW( file, ref fndData);
if(hFile.ToInt3 2() == -1)
Console.WriteLi ne("FindFirst: " + Marshal.GetLast Win32Error());
else
Console.WriteLi ne("Filename: " + fndData.cFileNa me_260);

}
}
}

Willy.