C# "Cannot have instance field initializers in Struct" error

Question

I am relatively new in C#, and I have a 2 classes. The first class has a public struct and the second one is trying to declare the struct. I am not good enough in english, but this is the code so that you may understand :

First Class :

class PE
{
#region NT Headers

    [StructLayout(LayoutKind.Explicit)]
    public struct IMAGE_NT_HEADERS32
    {
        [FieldOffset(0)]
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        public char[] Signature;

        [FieldOffset(4)]
        public IMAGE_FILE_HEADER FileHeader;

        [FieldOffset(24)]
        public IMAGE_OPTIONAL_HEADER32 OptionalHeader;
    }

    [StructLayout(LayoutKind.Explicit)]
    public struct IMAGE_NT_HEADERS64
    {
        [FieldOffset(0)]
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
        public char[] Signature;

        [FieldOffset(4)]
        public IMAGE_FILE_HEADER FileHeader;

        [FieldOffset(24)]
        public IMAGE_OPTIONAL_HEADER64 OptionalHeader;
    }
#endregion
}

Second Class :

class Main
{
    struct NT_Header
    {
        Namespace.PE.IMAGE_NT_HEADERS32 INTSIGN = 
            new Namespace.PE.IMAGE_NT_HEADERS32(); //HERE IS THE ERROR!
    }
}

It always raises the error... Thanks for helps!

Just to save you a bunch of time: Reading the Portable Executable (PE) Header in C# — Jonathon Reinhart
– Jonathon Reinhart, Commented Dec 22, 2012 at 2:53
Certainly, though, the compiler gives you a line number pointing you right to where the error is? Why have you omitted this, making it harder for us to help you? — Jonathon Reinhart
– Jonathon Reinhart, Commented Dec 22, 2012 at 2:53
yeah, but i just want to declare it in the second class, because i need it.. — newbie
– newbie, Commented Dec 22, 2012 at 2:54
it has an error at the main class, declaring the INTSIGN @Jontathon Reinhart — newbie
– newbie, Commented Dec 22, 2012 at 2:55

recursive · Accepted Answer · 2012-12-22 02:59:09Z

3

You can't assign a default value to a struct field, like you're doing in NT_Header. It's not legal C#. This would compile:

class Main
{
struct NT_Header
    {
        public Namespace.PE.IMAGE_NT_HEADERS32 INTSIGN;
    }
}

answered Dec 22, 2012 at 2:59

recursive

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3 Comments

nawfal Over a year ago

@newbie no, you're just a newbie :)

user1234567 Over a year ago

Why is it not allowed in C# ?

recursive Over a year ago

@user3241228: Because the language specification says it's not. If I had to guess why, it's because the default value of a struct type is always the same as the one produced by the default constructor, which is a memory-zeroed value. Imagine constructing a large array of these structs. There is never a chance to invoke the field initializers.

vamsee · Accepted Answer · 2013-07-14 17:51:27Z

-2

C# Compiler does not allow the inline initialization of value type instance fields. However, if you need to initialize a field, you need to mark it as "Static".

answered Jul 14, 2013 at 17:51

vamsee

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2 Comments

Gabe Over a year ago

If it's static, then it's no longer an instance field, and will not serve the purpose of what the OP was doing.

vamsee Over a year ago

I was trying to say C# Compiler allows value type to use only its static fields for inline initialization not the instance fields. Sorry for the confusion.

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