# Using cgo directly

Usage:

	go tool cgo [cgo options] [-- compiler options] gofiles...

Cgo transforms the specified input Go source files into several output
Go and C source files.

The compiler options are passed through uninterpreted when
invoking the C compiler to compile the C parts of the package.

The following options are available when running cgo directly:

	-V

				Content:  []byte("important \r\n"),
				Modified: time.Date(2011, 12, 8, 10, 6, 8, 0, timeZone(0)),
				Mode:     0444,
			},
		},
	},
	{
		// created by Go, before we wrote the "optional" data
		// descriptor signatures (which are required by macOS).
		// Use obscured file to avoid Apple’s notarization service
		// rejecting the toolchain due to an inability to unzip this archive.

}

var (
	D        MultiFlag
	I        MultiFlag
	PrintOut int
	DebugV   bool
)

func init() {
	flag.Var(&D, "D", "predefined symbol with optional simple value -D=identifier=value; can be set multiple times")
	flag.Var(&I, "I", "include directory; can be set multiple times")
	flag.BoolVar(&DebugV, "v", false, "print debug output")

Term        = production_name | token [ "…" token ] | Group | Option | Repetition .
Group       = "(" Expression ")" .
Option      = "[" Expression "]" .
Repetition  = "{" Expression "}" .
</pre>

<p>
Productions are expressions constructed from terms and the following
operators, in increasing precedence:
</p>
<pre class="grammar">
|   alternation
()  grouping
[]  option (0 or 1 times)
{}  repetition (0 to n times)
</pre>

		return
	}
	// General address (with a few exceptions) looks like
	//	$sym±offset(SB)(reg)(index*scale)
	// Exceptions are:
	//
	//	R1
	//	offset
	//	$offset
	// Every piece is optional, so we scan left to right and what
	// we discover tells us where we are.

	// Prefix: $.
	var prefix rune
	switch tok := p.peek(); tok {
	case '$', '*':
		prefix = rune(tok)
		p.next()
	}

	}
	return data
}

// ScanLines is a split function for a [Scanner] that returns each line of
// text, stripped of any trailing end-of-line marker. The returned line may
// be empty. The end-of-line marker is one optional carriage return followed
// by one mandatory newline. In regular expression notation, it is `\r?\n`.
// The last non-empty line of input will be returned even if it has no
// newline.

	}

	for i, n := range names {
		switch sniff[i] {
		default:
			if sniff[i]&notDeclared != 0 && optional[n] {
				// Ignore optional undeclared identifiers.
				// Don't report an error, and skip adding n to the needType array.
				continue
			}
			error_(f.NamePos[n], "could not determine kind of name for C.%s", fixGo(n.Go))

	paxHdrs = make(map[string]string)

	var whyNoUSTAR, whyNoPAX, whyNoGNU string
	var preferPAX bool // Prefer PAX over USTAR
	verifyString := func(s string, size int, name, paxKey string) {
		// NUL-terminator is optional for path and linkpath.
		// Technically, it is required for uname and gname,
		// but neither GNU nor BSD tar checks for it.
		tooLong := len(s) > size
		allowLongGNU := paxKey == paxPath || paxKey == paxLinkpath

The same assembler is used for all target operating systems and architectures.
The GOOS and GOARCH environment variables set the desired target.

Flags:

	-D name[=value]
		Predefine symbol name with an optional simple value.
		Can be repeated to define multiple symbols.
	-I dir1 -I dir2
		Search for #include files in dir1, dir2, etc,
		after consulting $GOROOT/pkg/$GOOS_$GOARCH.
	-S
		Print assembly and machine code.
	-V

The <code>DATA</code> directives for a given symbol must be written with increasing offsets.
</p>

<p>
The <code>GLOBL</code> directive declares a symbol to be global.
The arguments are optional flags and the size of the data being declared as a global,
which will have initial value all zeros unless a <code>DATA</code> directive
has initialized it.