[SOLVED] C# error: cannot use fixed size buffers contained in unfixed expressions

paulsm4 · 06-30-2011, 01:03 AM

Hi -

I'm struggling with a C# program to read binary records from a database. The records were created with Borland Delphi. Here's an example

Code:

// Delphi record definition
  tBowler_Rec = Record
  public
    gender          : tGender;
    bowler_num      : byte;
    name            : tString32;
    initials        : String[3];
    ...

Code:

// Corresponding C# definition (unmanaged code)
    [StructLayout(LayoutKind.Sequential, Pack=4)]
    public unsafe struct tBowler_Rec
    {
        public tGender gender;
        public byte bowler_num;
        public fixed byte name[32];
        public fixed byte initials[3];
        ...

I'm actually able to read this binary struct out of a SQL Server database and see the data in the Visual Studio debugger. Yay! I'm able to access fields like "gender" and "bowler_num" with no problem. Yay!

Q: How do I turn "name" into a C# string?

An example name is "ASHTON". It's a Pascal string (byte count, followed by ASCII characters). It looks like this in memory:

Code:

\0x6ASHTON\0x0\0x0...

Here's how I'm trying to access it:

Code:

[StructLayout(LayoutKind.Sequential, Pack=4)]
public unsafe struct tBowler_Rec
{
    public tGender gender;
    public byte bowler_num;
    public fixed byte name[32];
    ...
    public string Name
    {
        get
        {
            StringBuilder sb = new StringBuilder();
            int ilen = name[0];
            for (int i = 1; i <= ilen; i++)
                sb.Append(name[i]);
            return sb.ToString();
        }
    }

I'm getting this error:

Quote:

Error: You cannot use fixed size buffers contained in unfixed expressions. Try using the fixed statement.

Help?????

Thank you in advance!

paulsm4 · 06-30-2011, 02:02 PM

Hi -

I found the answer here:
http://stackoverflow.com/questions/6...om-this-object

Solution:

Code:

    [StructLayout(LayoutKind.Sequential, Pack=4)]
    public unsafe struct tBowler_Rec
    {
        public tGender gender;
        public byte bowler_num;
        [MarshalAs(UnmanagedType.ByValArray, SizeConst=32)]
        public byte[] name;
        ...
        public string Name
        {
            get
            {
                StringBuilder sb = new StringBuilder();
                int ilen = name[0];
                for (int i = 1; i <= ilen; i++)
                    sb.Append(name[i]);
                return sb.ToString();
            }
        }