IMAGE_OPTIONAL_HEADER

The IMAGE_OPTIONAL_HEADER structure represents the optional header format.

typedef struct _IMAGE_OPTIONAL_HEADER {
    WORD    Magic;
    BYTE    MajorLinkerVersion;
    BYTE    MinorLinkerVersion;
    DWORD   SizeOfCode;
    DWORD   SizeOfInitializedData;
    DWORD   SizeOfUninitializedData;
    DWORD   AddressOfEntryPoint;
    DWORD   BaseOfCode;
    DWORD   BaseOfData;
    DWORD   ImageBase;
    DWORD   SectionAlignment;
    DWORD   FileAlignment;
    WORD    MajorOperatingSystemVersion;
    WORD    MinorOperatingSystemVersion;
    WORD    MajorImageVersion;
    WORD    MinorImageVersion;
    WORD    MajorSubsystemVersion;
    WORD    MinorSubsystemVersion;
    DWORD   Win32VersionValue;
    DWORD   SizeOfImage;
    DWORD   SizeOfHeaders;
    DWORD   CheckSum;
    WORD    Subsystem;
    WORD    DllCharacteristics;
    DWORD   SizeOfStackReserve;
    DWORD   SizeOfStackCommit;
    DWORD   SizeOfHeapReserve;
    DWORD   SizeOfHeapCommit;
    DWORD   LoaderFlags;
    DWORD   NumberOfRvaAndSizes;
    IMAGE_DATA_DIRECTORY DataDirectory[IMAGE_NUMBEROF_DIRECTORY_ENTRIES];
} IMAGE_OPTIONAL_HEADER, *PIMAGE_OPTIONAL_HEADER;

Members

Magic

Specifies the state of the image file. This parameter may be one of the following values.

Value	Meaning
IMAGE_NT_OPTIONAL_HDR_MAGIC	The file is an executable image.
IMAGE_ROM_OPTIONAL_HDR_MAGIC	The file is a ROM image.

MajorLinkerVersion

Major version number of the linker.

MinorLinkerVersion

Minor version number of the linker.

SizeOfCode

The size of the code section, or the sum of all such sections if there are multiple code sections.

SizeOfInitializedData

The size of the initialized data section, or the sum of all such sections if there are multiple initialized data sections.

SizeOfUninitializedData

The size of the uninitialized data section, or the sum of all such sections if there are multiple uninitialized data sections.

AddressOfEntryPoint

Pointer to the entry point function, relative to the image base address. The entry point function is optional for DLLs. When no entry point is present, this member is zero.

BaseOfCode

Pointer to the beginning of the code section, relative to the image base.

BaseOfData

Pointer to the beginning of the data section, relative to the image base.

ImageBase

Preferred address of the first byte of the image when it is loaded in memory. This value is a multiple of 64K bytes. The default value for DLLs is 0x10000000. The default value for Win32-based applications on Windows CE is 0x00010000. The default value for Win32-based applications on Windows NT/Windows 2000 and Windows 95/98 is 0x00400000.

SectionAlignment

The alignment, in bytes, of sections loaded in memory. This value must be greater than or equal to the FileAlignment member. The default value is the page size for the system.

FileAlignment

The alignment, in bytes, of the raw data of sections in the image file. The value should be a power of 2 between 512 and 64K (inclusive). The default is 512. If the SectionAlignment member is less than the system page size, this member must be the same as SectionAlignment.

MajorOperatingSystemVersion

Major version number of the required operating system.

MinorOperatingSystemVersion

Minor version number of the required operating system.

MajorImageVersion

Major version number of the image.

MinorImageVersion

Minor version number of the image.

MajorSubsystemVersion

Major version number of the subsystem.

MinorSubsystemVersion

Minor version number of the subsystem.

Win32VersionValue

This member is reserved.

SizeOfImage

The size of the image, in bytes, including all headers. Must be a multiple of SectionAlignment.

SizeOfHeaders

Combined size of the MS-DOS stub, the PE header, and the section headers, rounded to a multiple of the value specified in the FileAlignment member.

CheckSum

Image file checksum.

Subsystem

Subsystem required to run this image. The following values are defined.

Subsystem	Description
IMAGE_SUBSYSTEM_UNKNOWN	Unknown subsystem.
IMAGE_SUBSYSTEM_NATIVE	No subsystem required.
IMAGE_SUBSYSTEM_WINDOWS_CUI	Windows character-mode subsystem.
IMAGE_SUBSYSTEM_POSIX_CUI	POSIX character-mode subsystem.
IMAGE_SUBSYSTEM_WINDOWS_CE_GUI	Windows CE.

DllCharacteristics

Specifies the DLL characteristics of the image. The following values are defined.

Value	Meaning
0x0001	Reserved
0x0002	Reserved
0x0004	Reserved
0x0008	Reserved
0x2000	A WDM driver.

SizeOfStackReserve

The number of bytes to reserve for the stack.

SizeOfStackCommit

The number of bytes to commit for the stack.

SizeOfHeapReserve

The number of bytes to reserve for the local heap.

SizeOfHeapCommit

The number of bytes to commit for the local heap.

LoaderFlags

This member is obsolete.

NumberOfRvaAndSizes

Number of directory entries.

DataDirectory

Pointer to the first IMAGE_DATA_DIRECTORY structure in the data directory.

Remarks

The number of directories is not fixed. Check the NumberOfRvaAndSizes member before looking for a specific directory.

Requirements

  Windows NT/2000: Requires Windows NT 4.0 or later.
  Windows 95/98: Requires Windows 95 or later. Available as a redistributable for Windows 95.
  Header: Declared in Winnt.h; include Windows.h.

See Also

Image Help Library Overview, ImageHlp Structures, IMAGE_DATA_DIRECTORY