field declaration. An empty tag string is equivalent to an absent tag.
The tags are made visible through a <a href="/pkg/reflect/#StructTag">reflection interface</a>
and take part in <a href="#Type_identity">type identity</a> for structs
but are otherwise ignored.
</p>

<pre>
struct {
	x, y float64 ""  // an empty tag string is like an absent tag
	name string  "any string is permitted as a tag"

field declaration. An empty tag string is equivalent to an absent tag.
The tags are made visible through a <a href="/pkg/reflect/#StructTag">reflection interface</a>
and take part in <a href="#Type_identity">type identity</a> for structs
but are otherwise ignored.
</p>

<pre>
struct {
	x, y float64 ""  // an empty tag string is like an absent tag
	name string  "any string is permitted as a tag"

C source.

Cgo first invokes gcc -E -dM on the preamble, in order to find out
about simple #defines for constants and the like. These are recorded
for later use.

Next, cgo needs to identify the kinds for each identifier. For the
identifiers C.foo, cgo generates this C program:

	<preamble>
	#line 1 "not-declared"
	void __cgo_f_1_1(void) { __typeof__(foo) *__cgo_undefined__1; }
	#line 1 "not-type"

)

func bytediff(a, b []byte) string {
	const (
		uniqueA  = "-  "
		uniqueB  = "+  "
		identity = "   "
	)
	var ss []string
	sa := strings.Split(strings.TrimSpace(hex.Dump(a)), "\n")
	sb := strings.Split(strings.TrimSpace(hex.Dump(b)), "\n")
	for len(sa) > 0 && len(sb) > 0 {
		if sa[0] == sb[0] {
			ss = append(ss, identity+sa[0])
		} else {
			ss = append(ss, uniqueA+sa[0])
			ss = append(ss, uniqueB+sb[0])
		}

// This assumes that 0.0 headers have already been converted to 0.1 headers
// by the PAX header parsing logic.
func (tr *Reader) readGNUSparsePAXHeaders(hdr *Header) (sparseDatas, error) {
	// Identify the version of GNU headers.
	var is1x0 bool
	major, minor := hdr.PAXRecords[paxGNUSparseMajor], hdr.PAXRecords[paxGNUSparseMinor]
	switch {
	case major == "0" && (minor == "0" || minor == "1"):
		is1x0 = false