Pass a C# struct with string to a C++ application

Question

I have a C# struct that I pass via UDP to a C++ application. I checked the length of a string field and got different results for the C# and C++ codes. Here are the definitions of the structs:

//  C# Side
//-------------
[StructLayout(LayoutKind.Sequential, Pack = 1)]
public struct stName
{
 /// Some data types
 [MarshalAs(UnmanagedType.ByValTstr, SizeConst = 20)]
 string StringName;
}

// C Side
//---------
struct stName{
/// Some data types
char StringName[20];

When StringName = "192.168.53.2" the size of that field at the C# side is 12 while it is 20 on the C side. What am I doing wrong? If C# uses the actual length of the string, what does the field SizeConst stand for?

you are passing a TString, you should use LPStr.

Daniel A. White
– Daniel A. White

2015-07-13 16:27:08 +00:00
Commented Jul 13, 2015 at 16:27 — Daniel A. White
– Daniel A. White, Commented Jul 13, 2015 at 16:27

Jashaszun · Accepted Answer · 2015-07-13 16:27:32Z

1

When you check the length of the string in C#, it counts the number of characters (192.168.53.2 is, correctly, 12 characters long).

However, in C, a string is really just an array of characters which is null-terminated. However, the size of the array in this case is just what you set it to, which is 20. So the size of this "field" is 20.

The SizeConst field refers to the size of the C array, so that the interop can create the C array appropriately (with the correct total size).

answered Jul 13, 2015 at 16:27

Jashaszun

9,2503 gold badges31 silver badges58 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Pass a C# struct with string to a C++ application

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related