int FIELDOFFSET(type,field)
The FIELDOFFSET macro computes the address offset of the specified member in the structure specified by the type parameter.
type
Specifies the name of the structure.
field
Specifies the name of the member defined within the given structure.
The return value is the address offset of the given structure member.
The FIELDOFFSET macro is defined in WINDOWS.H as follows:
#define FIELDOFFSET(type, field) ((int)(&((type NEAR*)1)->field)-1)