Get byte offset of a field in a structure — ffi

Returns the byte offset of a field within a structure, accounting for alignment requirements. Similar to C's offsetof() macro.

Usage

ffi_offsetof(struct_type, field, use_pack = TRUE)

Arguments

struct_type: StructType object
field: Character field name or integer field index (1-based)
use_pack: Logical, whether to use the struct's pack setting. Default TRUE. Set to FALSE to get libffi's natural alignment offset even for packed structs.

Value

Integer byte offset

Details

For packed structures (created with pack parameter), this function computes the offset using the specified packing alignment rather than natural alignment.

Examples

if (FALSE) { # \dontrun{
Point <- ffi_struct(x = ffi_int(), y = ffi_double())
ffi_offsetof(Point, "x") # 0
ffi_offsetof(Point, "y") # 8 (aligned to 8-byte boundary)

# Packed struct example
Packed <- ffi_struct(a = ffi_uint8(), b = ffi_int32(), .pack = 1)
ffi_offsetof(Packed, "b") # 1 (no padding with .pack=1)
} # }