How to create a value typed Struct with strings?-CodePudding

I want to read a MemoryMappedFile with a struct. Strings are located in this file. So I created a struct like this:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct MemMappedFile
{
    
    [...]
    
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 15)]
    public string SomeString;

    [...]
}

I get the error

System.ArgumentException: The specified Type must be a struct containing no references.

From my understanding the string is a reference type but the marshaling should manage this, but it doesn't - probably I am using it wrong.

How can I use a string in a struct, which needs to be out of value types only?

CodePudding user response：

The string itself is not stored in the struct. Instead a reference to the string is stored in the struct, so the struct size never changes.

string is not a value type; .NET strings are interned, which means that each unique string is stored in a look-up table in memory.

CodePudding user response：

@Heinzi's answer was correct.

I had to use byte[] and use an unsafe context.