P/Invoke, c#: unsigned char losing a byte

Question

Im working towards a dll file for a software's SDK and i'm trying to call a function to get information about the host of the software.

there are two unsigned char variables(HostMachineAddress, HostProgramVersion) in the struct the function wants and it seems like i "loose" the last byte when i try to call it from c#... if I change the SizeConst in the c# struct below to 5 i do get the missing byte, however it causes the other variable looses data.

Could someone help me find a way to solve this issue? also trying to use a class instead of struct causes system.stackoverflow error

C# Struct

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct sHostInfo
{
    public int bFoundHost;
    public int LatestConfirmationTime;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
    public string szHostMachineName;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 4)]
    public string HostMachineAddress;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
    public string szHostProgramName;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 4)]
    public string HostProgramVersion;
}

C#

[DllImport("Cortex_SDK.dll")]
public static extern int GetHostInfo(out sHostInfo pHostInfo);

Why are HostProgramVersion and szHostProgramName swapped in your C# code? — Fox32

Jaroslav Jandek Jaroslav Jandek · Accepted Answer · 2011-03-07T15:48:38

Your C# struct's layout is different from the C++ one (HostProgramVersion should be last).

Also for strings marshalled as ByValTStr use [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)].

The problem with the missing last byte may be that the marshaller tries to append null to your string (as in null-terminated string). Try to use sbyte[]+ByValArray instead of a string.

P/Invoke, c#: unsigned char losing a byte

1 Answers