parsing these is significantly less work and more robust than parsing
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"

</ol>

<p>
Blocks nest and influence <a href="#Declarations_and_scope">scoping</a>.
</p>


<h2 id="Declarations_and_scope">Declarations and scope</h2>

<p>
A <i>declaration</i> binds a non-<a href="#Blank_identifier">blank</a> identifier to a
<a href="#Constant_declarations">constant</a>,
<a href="#Type_declarations">type</a>,
<a href="#Variable_declarations">variable</a>,

	// data that describes the next file. These meta data "files" should not
	// normally be visible to the outside. As such, this loop iterates through
	// one or more "header files" until it finds a "normal file".
	format := FormatUSTAR | FormatPAX | FormatGNU
	for {
		// Discard the remainder of the file and any padding.
		if err := discard(tr.r, tr.curr.physicalRemaining()); err != nil {
			return nil, err
		}

		return nil
	})
	if err != nil {
		log.Fatal(err)
	}
	if err := zw.Close(); err != nil {
		log.Fatal(err)
	}
	if len(seen) == 0 {
		log.Fatalf("did not find any files to add")
	}
	if !seen["US/Eastern"] {
		log.Fatalf("did not find US/Eastern to add")
	}
	if err := os.WriteFile(args[0], zb.Bytes(), 0666); err != nil {
		log.Fatal(err)
	}

then fixing the bug will break that code.
New features can also have similar impacts:
enabling the HTTP/2 use by the HTTP client broke programs
connecting to servers with buggy HTTP/2 implementations.
These kinds of changes are unavoidable and
[permitted by the Go 1 compatibility rules](/doc/go1compat).
Even so, Go provides a mechanism called GODEBUG to
reduce the impact such changes have on Go developers

	// Prefer Equal to Compare for equality comparisons.
	if bytes.Equal(a, b) {
		// a equal b
	}
	if !bytes.Equal(a, b) {
		// a not equal b
	}
}

func ExampleCompare_search() {
	// Binary search to find a matching byte slice.
	var needle []byte
	var haystack [][]byte // Assume sorted
	i := sort.Search(len(haystack), func(i int) bool {
		// Return haystack[i] >= needle.
		return bytes.Compare(haystack[i], needle) >= 0

	d := make([]byte, 1024)
	if _, err := zip.ReadAt(d, zip.Size()-int64(len(d))); err != nil {
		t.Fatalf("ReadAt: %v", err)
	}

	sigOff := findSignatureInBlock(d)
	if sigOff == -1 {
		t.Errorf("failed to find signature in block")
		return false
	}

	dirOff, err := findDirectory64End(zip, zip.Size()-int64(len(d))+int64(sigOff))
	if err != nil {
		t.Fatalf("findDirectory64End: %v", err)
	}
	if dirOff == -1 {

</ol>

<p>
Blocks nest and influence <a href="#Declarations_and_scope">scoping</a>.
</p>


<h2 id="Declarations_and_scope">Declarations and scope</h2>

<p>
A <i>declaration</i> binds a non-<a href="#Blank_identifier">blank</a> identifier to a
<a href="#Constant_declarations">constant</a>,
<a href="#Type_declarations">type</a>,
<a href="#Type_parameter_declarations">type parameter</a>,