{{fbdoc item="title" value="Structure layout"}}

Structure layout must match the target ABI when FreeBASIC code talks to C
libraries, system calls, graphics backends, sound backends, or binary file
formats. Do not assume that a structure layout proven on one CPU is correct on
another CPU.

{{fbdoc item="subsect" value="What affects layout"}}

	Field type and size.
	Field alignment.
	Structure packing.
	Pointer size.
	Calling convention and ABI family.
	Compiler-specific C headers for the target platform.

{{fbdoc item="subsect" value="Modern targets"}}

Layout-sensitive code should be checked on every advertised CPU family. That
includes 32-bit and 64-bit x86, ARM, AArch64, PowerPC-family targets,
MIPS-family targets, s390x, WebAssembly/JavaScript where applicable, and the
BSD, Haiku, Solaris-like, DOS, Windows, and mobile targets supported by the
tree.

{{fbdoc item="subsect" value="Practical rule"}}

When a structure is shared with C, prefer a tiny C probe or a FreeBASIC test that
checks ##sizeof## and important field offsets on the real target. Guessing from
a similar platform is not enough for release work.