# 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

pkg net/http, const MethodGet = "GET"
pkg net/http, const MethodGet ideal-string
pkg net/http, const MethodHead = "HEAD"
pkg net/http, const MethodHead ideal-string
pkg net/http, const MethodOptions = "OPTIONS"
pkg net/http, const MethodOptions ideal-string
pkg net/http, const MethodPatch = "PATCH"
pkg net/http, const MethodPatch ideal-string
pkg net/http, const MethodPost = "POST"
pkg net/http, const MethodPost ideal-string

### Go 1.21

Go 1.21 made it a run-time error to call `panic` with a nil interface value,
controlled by the [`panicnil` setting](/pkg/builtin/#panic).

Go 1.21 made it an error for html/template actions to appear inside of an ECMAScript 6
template literal, controlled by the
[`jstmpllitinterp` setting](/pkg/html/template#hdr-Security_Model).
This behavior was backported to Go 1.19.8+ and Go 1.20.3+.

	if tw.err != nil {
		return tw.err
	}

	// Trailer: two zero blocks.
	err := tw.Flush()
	for i := 0; i < 2 && err == nil; i++ {
		_, err = tw.w.Write(zeroBlock[:])
	}

	// Ensure all future actions are invalid.
	tw.err = ErrWriteAfterClose
	return err // Report IO errors
}

// regFileWriter is a fileWriter for writing data to a regular file entry.
type regFileWriter struct {