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Writing Structures To Binary Files

I am porting an application from C++ to C#, and am having trouble finding a way to quickly and efficiently write structures to a binary file. In C++ this is trivial because all that is necessary is to pack the structure to 1 byte boundries, and then just write out the structure directly to the File IO function

pragma pack (1

typedef struct
char var1[4]
int var1

fwrite(&myStruc ture,sizeof(MyS truct),1,filepo inter);
Things are clearly different in C# however(and .NET in general). I am using a FileStream(with a 4k buffer for maximum file performance) and it only writes byte arrays. So I think the only issue is how to efficiently turn a structure into a byte array

I know one can marshall the data into a byte array like so

[StructLayout(La youtKind.Sequen tial, Pack = 1)
public struct MyStruc

[MarshalAs(Unman agedType.ByValA rray, SizeConst=4)]
public char[] var1;
public int var2
public class ByteManipulatio

/// <summary
/// Marshals data from an object to an array of bytes
/// </summary
/// <param name="obj">The object to be serialized</param
/// <returns>Arra y of bytes</returns
public static byte[] SerializeObject ToBytes(object obj

int size = Marshal.SizeOf( obj );
IntPtr buffer = Marshal.AllocHG lobal( size );
Marshal.Structu reToPtr( obj, buffer, false );
byte[] data = new byte[ size ];
Marshal.Copy( buffer, data, 0, size );
Marshal.FreeHGl obal( buffer );
return data

but this has 2 problems for my application, 1 it is slow, and 2, it does not work because the Marshall.Sizeof () call fails because of the arrays in the structure (even with the MarshallAs attribute, it compiles fine but I get a runtime error

It would be preferable performance wise for me to use an unsafe block


fixed(byte *pData = *(byte*)myStruc t

but I keep getting an error that I cannot convert MyStruct to byte*.

Am I casting wrong in the unsafe block? There has to be a way to do this. All I want to do is get myStruct into a byte[]..

Also, I know one can use serialization to stuff objects into binary files, but I am unsure of the formatting effects of the serialization formatter. I need to control the format of the binary file - does the serialization add bytes to the file in any way that would confilct with a well defined file format

Thank you in advance for your help
Nov 16 '05 #1
2 7806
phyzics wrote:
fixed(byte *pData = *(byte*)myStruc t)


but I keep getting an error that I cannot convert MyStruct to byte*.

You need a pointer of myStruct first, to convert it to byte*. Try using

fixed(byte *pData = (byte*)&myStruc t)
which would be the C++-way to do this but as I've never worked in C#
unsafe mode I can't say if that'll do it.

Konrad -
Nov 16 '05 #2
Thanks for your reply, but this does not work:

the following code results in an error

fixed(byte *pData = (byte*)&myStruc t
that states that the right hand side cannot be a cast expression. Ok, so I'll try not typecasting..

fixed(byte *pData = &myStruct
This generates an error that states that MyStruct cannot implicitly be converted to byte*

Any suggestions to go from here

----- Konrad L. M. Rudolph wrote: ----

phyzics wrote

fixed(byte *pData = *(byte*)myStruc t

but I keep getting an error that I cannot convert MyStruct to byte*.

You need a pointer of myStruct first, to convert it to byte*. Try usin

\\ fixed(byte *pData = (byte*)&myStruc t
which would be the C++-way to do this but as I've never worked in C#
unsafe mode I can't say if that'll do it

Nov 16 '05 #3

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