C# get the size of a struct

Question

Well, it's about PE. I want to know the exact size of IMAGE_DOS_HEADER struct and the NT Header struct. I used Marshal.SizeOf but it doesn't work.

Image_Dos_Header struct

    public struct IMAGE_DOS_HEADER
    {      // DOS .EXE header
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
        public UInt16 e_magic;              // Magic number
        public UInt16 e_cblp;               // Bytes on last page of file
        public UInt16 e_cp;                 // Pages in file
        public UInt16 e_crlc;               // Relocations
        public UInt16 e_cparhdr;            // Size of header in paragraphs
        public UInt16 e_minalloc;           // Minimum extra paragraphs needed
        public UInt16 e_maxalloc;           // Maximum extra paragraphs needed
        public UInt16 e_ss;                 // Initial (relative) SS value
        public UInt16 e_sp;                 // Initial SP value
        public UInt16 e_csum;               // Checksum
        public UInt16 e_ip;                 // Initial IP value
        public UInt16 e_cs;                 // Initial (relative) CS value
        public UInt16 e_lfarlc;             // File address of relocation table
        public UInt16 e_ovno;               // Overlay number
        public UInt16 e_res_0;              // Reserved words
        public UInt16 e_res_1;              // Reserved words
        public UInt16 e_res_2;              // Reserved words
        public UInt16 e_res_3;              // Reserved words
        public UInt16 e_oemid;              // OEM identifier (for e_oeminfo)
        public UInt16 e_oeminfo;            // OEM information; e_oemid specific
        public UInt16 e_res2_0;             // Reserved words
        public UInt16 e_res2_1;             // Reserved words
        public UInt16 e_res2_2;             // Reserved words
        public UInt16 e_res2_3;             // Reserved words
        public UInt16 e_res2_4;             // Reserved words
        public UInt16 e_res2_5;             // Reserved words
        public UInt16 e_res2_6;             // Reserved words
        public UInt16 e_res2_7;             // Reserved words
        public UInt16 e_res2_8;             // Reserved words
        public UInt16 e_res2_9;             // Reserved words
        public UInt32 e_lfanew;             // File address of new exe header
    }

And this is the NTHeader struct

        [StructLayout(LayoutKind.Sequential)]
    public struct IMAGE_NT_HEADERS
    {
        public IMAGE_FILE_HEADER FileHeader;
        public IMAGE_OPTIONAL_HEADER32 OptionalHeader32;
        public IMAGE_NT_HEADERS32 INTSIGN;
     }

    [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.Sequential, Pack = 1)]
    public struct IMAGE_OPTIONAL_HEADER32
    {
        public UInt16 Magic;
        public Byte MajorLinkerVersion;
        public Byte MinorLinkerVersion;
        public UInt32 SizeOfCode;
        public UInt32 SizeOfInitializedData;
        public UInt32 SizeOfUninitializedData;
        public UInt32 AddressOfEntryPoint;
        public UInt32 BaseOfCode;
        public UInt32 BaseOfData;
        public UInt32 ImageBase;
        public UInt32 SectionAlignment;
        public UInt32 FileAlignment;
        public UInt16 MajorOperatingSystemVersion;
        public UInt16 MinorOperatingSystemVersion;
        public UInt16 MajorImageVersion;
        public UInt16 MinorImageVersion;
        public UInt16 MajorSubsystemVersion;
        public UInt16 MinorSubsystemVersion;
        public UInt32 Win32VersionValue;
        public UInt32 SizeOfImage;
        public UInt32 SizeOfHeaders;
        public UInt32 CheckSum;
        public UInt16 Subsystem;
        public UInt16 DllCharacteristics;
        public UInt32 SizeOfStackReserve;
        public UInt32 SizeOfStackCommit;
        public UInt32 SizeOfHeapReserve;
        public UInt32 SizeOfHeapCommit;
        public UInt32 LoaderFlags;
        public UInt32 NumberOfRvaAndSizes;

        public IMAGE_DATA_DIRECTORY ExportTable;
        public IMAGE_DATA_DIRECTORY ImportTable;
        public IMAGE_DATA_DIRECTORY ResourceTable;
        public IMAGE_DATA_DIRECTORY ExceptionTable;
        public IMAGE_DATA_DIRECTORY CertificateTable;
        public IMAGE_DATA_DIRECTORY BaseRelocationTable;
        public IMAGE_DATA_DIRECTORY Debug;
        public IMAGE_DATA_DIRECTORY Architecture;
        public IMAGE_DATA_DIRECTORY GlobalPtr;
        public IMAGE_DATA_DIRECTORY TLSTable;
        public IMAGE_DATA_DIRECTORY LoadConfigTable;
        public IMAGE_DATA_DIRECTORY BoundImport;
        public IMAGE_DATA_DIRECTORY IAT;
        public IMAGE_DATA_DIRECTORY DelayImportDescriptor;
        public IMAGE_DATA_DIRECTORY CLRRuntimeHeader;
        public IMAGE_DATA_DIRECTORY Reserved;
    }
        [StructLayout(LayoutKind.Sequential, Pack = 1)]
        public struct IMAGE_FILE_HEADER
    {
        public UInt16 Machine;
        public UInt16 NumberOfSections;
        public UInt32 TimeDateStamp;
        public UInt32 PointerToSymbolTable;
        public UInt32 NumberOfSymbols;
        public UInt16 SizeOfOptionalHeader;
        public UInt16 Characteristics;
    }

Thanks for helps! I tried to find since hours ago and I still can't find the solution. Sorry for bad english and sorry for asking this. I'm still new in c#

Answer 1

This works fine for me.

Notice the unsafe modifier for the Main method, you need to add that for normal sizeof to work. You also need to enable unsafe code in your project for this to compile.

unsafe public static void Main(string[] args)
{
    Console.WriteLine(sizeof(IMAGE_DOS_HEADER)); //64
    Console.Read();
}


public struct IMAGE_DOS_HEADER
{      // DOS .EXE header
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 2)]
    public UInt16 e_magic;              // Magic number
    public UInt16 e_cblp;               // Bytes on last page of file
    public UInt16 e_cp;                 // Pages in file
    public UInt16 e_crlc;               // Relocations
    public UInt16 e_cparhdr;            // Size of header in paragraphs
    public UInt16 e_minalloc;           // Minimum extra paragraphs needed
    public UInt16 e_maxalloc;           // Maximum extra paragraphs needed
    public UInt16 e_ss;                 // Initial (relative) SS value
    public UInt16 e_sp;                 // Initial SP value
    public UInt16 e_csum;               // Checksum
    public UInt16 e_ip;                 // Initial IP value
    public UInt16 e_cs;                 // Initial (relative) CS value
    public UInt16 e_lfarlc;             // File address of relocation table
    public UInt16 e_ovno;               // Overlay number
    public UInt16 e_res_0;              // Reserved words
    public UInt16 e_res_1;              // Reserved words
    public UInt16 e_res_2;              // Reserved words
    public UInt16 e_res_3;              // Reserved words
    public UInt16 e_oemid;              // OEM identifier (for e_oeminfo)
    public UInt16 e_oeminfo;            // OEM information; e_oemid specific
    public UInt16 e_res2_0;             // Reserved words
    public UInt16 e_res2_1;             // Reserved words
    public UInt16 e_res2_2;             // Reserved words
    public UInt16 e_res2_3;             // Reserved words
    public UInt16 e_res2_4;             // Reserved words
    public UInt16 e_res2_5;             // Reserved words
    public UInt16 e_res2_6;             // Reserved words
    public UInt16 e_res2_7;             // Reserved words
    public UInt16 e_res2_8;             // Reserved words
    public UInt16 e_res2_9;             // Reserved words
    public UInt32 e_lfanew;             // File address of new exe header
}