Source file src/fmt/print.go

Documentation: fmt

		 1  // Copyright 2009 The Go Authors. All rights reserved.
		 2  // Use of this source code is governed by a BSD-style
		 3  // license that can be found in the LICENSE file.
		 4  
		 5  package fmt
		 6  
		 7  import (
		 8  	"internal/fmtsort"
		 9  	"io"
		10  	"os"
		11  	"reflect"
		12  	"sync"
		13  	"unicode/utf8"
		14  )
		15  
		16  // Strings for use with buffer.WriteString.
		17  // This is less overhead than using buffer.Write with byte arrays.
		18  const (
		19  	commaSpaceString	= ", "
		20  	nilAngleString		= "<nil>"
		21  	nilParenString		= "(nil)"
		22  	nilString				 = "nil"
		23  	mapString				 = "map["
		24  	percentBangString = "%!"
		25  	missingString		 = "(MISSING)"
		26  	badIndexString		= "(BADINDEX)"
		27  	panicString			 = "(PANIC="
		28  	extraString			 = "%!(EXTRA "
		29  	badWidthString		= "%!(BADWIDTH)"
		30  	badPrecString		 = "%!(BADPREC)"
		31  	noVerbString			= "%!(NOVERB)"
		32  	invReflectString	= "<invalid reflect.Value>"
		33  )
		34  
		35  // State represents the printer state passed to custom formatters.
		36  // It provides access to the io.Writer interface plus information about
		37  // the flags and options for the operand's format specifier.
		38  type State interface {
		39  	// Write is the function to call to emit formatted output to be printed.
		40  	Write(b []byte) (n int, err error)
		41  	// Width returns the value of the width option and whether it has been set.
		42  	Width() (wid int, ok bool)
		43  	// Precision returns the value of the precision option and whether it has been set.
		44  	Precision() (prec int, ok bool)
		45  
		46  	// Flag reports whether the flag c, a character, has been set.
		47  	Flag(c int) bool
		48  }
		49  
		50  // Formatter is implemented by any value that has a Format method.
		51  // The implementation controls how State and rune are interpreted,
		52  // and may call Sprint(f) or Fprint(f) etc. to generate its output.
		53  type Formatter interface {
		54  	Format(f State, verb rune)
		55  }
		56  
		57  // Stringer is implemented by any value that has a String method,
		58  // which defines the ``native'' format for that value.
		59  // The String method is used to print values passed as an operand
		60  // to any format that accepts a string or to an unformatted printer
		61  // such as Print.
		62  type Stringer interface {
		63  	String() string
		64  }
		65  
		66  // GoStringer is implemented by any value that has a GoString method,
		67  // which defines the Go syntax for that value.
		68  // The GoString method is used to print values passed as an operand
		69  // to a %#v format.
		70  type GoStringer interface {
		71  	GoString() string
		72  }
		73  
		74  // Use simple []byte instead of bytes.Buffer to avoid large dependency.
		75  type buffer []byte
		76  
		77  func (b *buffer) write(p []byte) {
		78  	*b = append(*b, p...)
		79  }
		80  
		81  func (b *buffer) writeString(s string) {
		82  	*b = append(*b, s...)
		83  }
		84  
		85  func (b *buffer) writeByte(c byte) {
		86  	*b = append(*b, c)
		87  }
		88  
		89  func (bp *buffer) writeRune(r rune) {
		90  	if r < utf8.RuneSelf {
		91  		*bp = append(*bp, byte(r))
		92  		return
		93  	}
		94  
		95  	b := *bp
		96  	n := len(b)
		97  	for n+utf8.UTFMax > cap(b) {
		98  		b = append(b, 0)
		99  	}
	 100  	w := utf8.EncodeRune(b[n:n+utf8.UTFMax], r)
	 101  	*bp = b[:n+w]
	 102  }
	 103  
	 104  // pp is used to store a printer's state and is reused with sync.Pool to avoid allocations.
	 105  type pp struct {
	 106  	buf buffer
	 107  
	 108  	// arg holds the current item, as an interface{}.
	 109  	arg interface{}
	 110  
	 111  	// value is used instead of arg for reflect values.
	 112  	value reflect.Value
	 113  
	 114  	// fmt is used to format basic items such as integers or strings.
	 115  	fmt fmt
	 116  
	 117  	// reordered records whether the format string used argument reordering.
	 118  	reordered bool
	 119  	// goodArgNum records whether the most recent reordering directive was valid.
	 120  	goodArgNum bool
	 121  	// panicking is set by catchPanic to avoid infinite panic, recover, panic, ... recursion.
	 122  	panicking bool
	 123  	// erroring is set when printing an error string to guard against calling handleMethods.
	 124  	erroring bool
	 125  	// wrapErrs is set when the format string may contain a %w verb.
	 126  	wrapErrs bool
	 127  	// wrappedErr records the target of the %w verb.
	 128  	wrappedErr error
	 129  }
	 130  
	 131  var ppFree = sync.Pool{
	 132  	New: func() interface{} { return new(pp) },
	 133  }
	 134  
	 135  // newPrinter allocates a new pp struct or grabs a cached one.
	 136  func newPrinter() *pp {
	 137  	p := ppFree.Get().(*pp)
	 138  	p.panicking = false
	 139  	p.erroring = false
	 140  	p.wrapErrs = false
	 141  	p.fmt.init(&p.buf)
	 142  	return p
	 143  }
	 144  
	 145  // free saves used pp structs in ppFree; avoids an allocation per invocation.
	 146  func (p *pp) free() {
	 147  	// Proper usage of a sync.Pool requires each entry to have approximately
	 148  	// the same memory cost. To obtain this property when the stored type
	 149  	// contains a variably-sized buffer, we add a hard limit on the maximum buffer
	 150  	// to place back in the pool.
	 151  	//
	 152  	// See https://golang.org/issue/23199
	 153  	if cap(p.buf) > 64<<10 {
	 154  		return
	 155  	}
	 156  
	 157  	p.buf = p.buf[:0]
	 158  	p.arg = nil
	 159  	p.value = reflect.Value{}
	 160  	p.wrappedErr = nil
	 161  	ppFree.Put(p)
	 162  }
	 163  
	 164  func (p *pp) Width() (wid int, ok bool) { return p.fmt.wid, p.fmt.widPresent }
	 165  
	 166  func (p *pp) Precision() (prec int, ok bool) { return p.fmt.prec, p.fmt.precPresent }
	 167  
	 168  func (p *pp) Flag(b int) bool {
	 169  	switch b {
	 170  	case '-':
	 171  		return p.fmt.minus
	 172  	case '+':
	 173  		return p.fmt.plus || p.fmt.plusV
	 174  	case '#':
	 175  		return p.fmt.sharp || p.fmt.sharpV
	 176  	case ' ':
	 177  		return p.fmt.space
	 178  	case '0':
	 179  		return p.fmt.zero
	 180  	}
	 181  	return false
	 182  }
	 183  
	 184  // Implement Write so we can call Fprintf on a pp (through State), for
	 185  // recursive use in custom verbs.
	 186  func (p *pp) Write(b []byte) (ret int, err error) {
	 187  	p.buf.write(b)
	 188  	return len(b), nil
	 189  }
	 190  
	 191  // Implement WriteString so that we can call io.WriteString
	 192  // on a pp (through state), for efficiency.
	 193  func (p *pp) WriteString(s string) (ret int, err error) {
	 194  	p.buf.writeString(s)
	 195  	return len(s), nil
	 196  }
	 197  
	 198  // These routines end in 'f' and take a format string.
	 199  
	 200  // Fprintf formats according to a format specifier and writes to w.
	 201  // It returns the number of bytes written and any write error encountered.
	 202  func Fprintf(w io.Writer, format string, a ...interface{}) (n int, err error) {
	 203  	p := newPrinter()
	 204  	p.doPrintf(format, a)
	 205  	n, err = w.Write(p.buf)
	 206  	p.free()
	 207  	return
	 208  }
	 209  
	 210  // Printf formats according to a format specifier and writes to standard output.
	 211  // It returns the number of bytes written and any write error encountered.
	 212  func Printf(format string, a ...interface{}) (n int, err error) {
	 213  	return Fprintf(os.Stdout, format, a...)
	 214  }
	 215  
	 216  // Sprintf formats according to a format specifier and returns the resulting string.
	 217  func Sprintf(format string, a ...interface{}) string {
	 218  	p := newPrinter()
	 219  	p.doPrintf(format, a)
	 220  	s := string(p.buf)
	 221  	p.free()
	 222  	return s
	 223  }
	 224  
	 225  // These routines do not take a format string
	 226  
	 227  // Fprint formats using the default formats for its operands and writes to w.
	 228  // Spaces are added between operands when neither is a string.
	 229  // It returns the number of bytes written and any write error encountered.
	 230  func Fprint(w io.Writer, a ...interface{}) (n int, err error) {
	 231  	p := newPrinter()
	 232  	p.doPrint(a)
	 233  	n, err = w.Write(p.buf)
	 234  	p.free()
	 235  	return
	 236  }
	 237  
	 238  // Print formats using the default formats for its operands and writes to standard output.
	 239  // Spaces are added between operands when neither is a string.
	 240  // It returns the number of bytes written and any write error encountered.
	 241  func Print(a ...interface{}) (n int, err error) {
	 242  	return Fprint(os.Stdout, a...)
	 243  }
	 244  
	 245  // Sprint formats using the default formats for its operands and returns the resulting string.
	 246  // Spaces are added between operands when neither is a string.
	 247  func Sprint(a ...interface{}) string {
	 248  	p := newPrinter()
	 249  	p.doPrint(a)
	 250  	s := string(p.buf)
	 251  	p.free()
	 252  	return s
	 253  }
	 254  
	 255  // These routines end in 'ln', do not take a format string,
	 256  // always add spaces between operands, and add a newline
	 257  // after the last operand.
	 258  
	 259  // Fprintln formats using the default formats for its operands and writes to w.
	 260  // Spaces are always added between operands and a newline is appended.
	 261  // It returns the number of bytes written and any write error encountered.
	 262  func Fprintln(w io.Writer, a ...interface{}) (n int, err error) {
	 263  	p := newPrinter()
	 264  	p.doPrintln(a)
	 265  	n, err = w.Write(p.buf)
	 266  	p.free()
	 267  	return
	 268  }
	 269  
	 270  // Println formats using the default formats for its operands and writes to standard output.
	 271  // Spaces are always added between operands and a newline is appended.
	 272  // It returns the number of bytes written and any write error encountered.
	 273  func Println(a ...interface{}) (n int, err error) {
	 274  	return Fprintln(os.Stdout, a...)
	 275  }
	 276  
	 277  // Sprintln formats using the default formats for its operands and returns the resulting string.
	 278  // Spaces are always added between operands and a newline is appended.
	 279  func Sprintln(a ...interface{}) string {
	 280  	p := newPrinter()
	 281  	p.doPrintln(a)
	 282  	s := string(p.buf)
	 283  	p.free()
	 284  	return s
	 285  }
	 286  
	 287  // getField gets the i'th field of the struct value.
	 288  // If the field is itself is an interface, return a value for
	 289  // the thing inside the interface, not the interface itself.
	 290  func getField(v reflect.Value, i int) reflect.Value {
	 291  	val := v.Field(i)
	 292  	if val.Kind() == reflect.Interface && !val.IsNil() {
	 293  		val = val.Elem()
	 294  	}
	 295  	return val
	 296  }
	 297  
	 298  // tooLarge reports whether the magnitude of the integer is
	 299  // too large to be used as a formatting width or precision.
	 300  func tooLarge(x int) bool {
	 301  	const max int = 1e6
	 302  	return x > max || x < -max
	 303  }
	 304  
	 305  // parsenum converts ASCII to integer.	num is 0 (and isnum is false) if no number present.
	 306  func parsenum(s string, start, end int) (num int, isnum bool, newi int) {
	 307  	if start >= end {
	 308  		return 0, false, end
	 309  	}
	 310  	for newi = start; newi < end && '0' <= s[newi] && s[newi] <= '9'; newi++ {
	 311  		if tooLarge(num) {
	 312  			return 0, false, end // Overflow; crazy long number most likely.
	 313  		}
	 314  		num = num*10 + int(s[newi]-'0')
	 315  		isnum = true
	 316  	}
	 317  	return
	 318  }
	 319  
	 320  func (p *pp) unknownType(v reflect.Value) {
	 321  	if !v.IsValid() {
	 322  		p.buf.writeString(nilAngleString)
	 323  		return
	 324  	}
	 325  	p.buf.writeByte('?')
	 326  	p.buf.writeString(v.Type().String())
	 327  	p.buf.writeByte('?')
	 328  }
	 329  
	 330  func (p *pp) badVerb(verb rune) {
	 331  	p.erroring = true
	 332  	p.buf.writeString(percentBangString)
	 333  	p.buf.writeRune(verb)
	 334  	p.buf.writeByte('(')
	 335  	switch {
	 336  	case p.arg != nil:
	 337  		p.buf.writeString(reflect.TypeOf(p.arg).String())
	 338  		p.buf.writeByte('=')
	 339  		p.printArg(p.arg, 'v')
	 340  	case p.value.IsValid():
	 341  		p.buf.writeString(p.value.Type().String())
	 342  		p.buf.writeByte('=')
	 343  		p.printValue(p.value, 'v', 0)
	 344  	default:
	 345  		p.buf.writeString(nilAngleString)
	 346  	}
	 347  	p.buf.writeByte(')')
	 348  	p.erroring = false
	 349  }
	 350  
	 351  func (p *pp) fmtBool(v bool, verb rune) {
	 352  	switch verb {
	 353  	case 't', 'v':
	 354  		p.fmt.fmtBoolean(v)
	 355  	default:
	 356  		p.badVerb(verb)
	 357  	}
	 358  }
	 359  
	 360  // fmt0x64 formats a uint64 in hexadecimal and prefixes it with 0x or
	 361  // not, as requested, by temporarily setting the sharp flag.
	 362  func (p *pp) fmt0x64(v uint64, leading0x bool) {
	 363  	sharp := p.fmt.sharp
	 364  	p.fmt.sharp = leading0x
	 365  	p.fmt.fmtInteger(v, 16, unsigned, 'v', ldigits)
	 366  	p.fmt.sharp = sharp
	 367  }
	 368  
	 369  // fmtInteger formats a signed or unsigned integer.
	 370  func (p *pp) fmtInteger(v uint64, isSigned bool, verb rune) {
	 371  	switch verb {
	 372  	case 'v':
	 373  		if p.fmt.sharpV && !isSigned {
	 374  			p.fmt0x64(v, true)
	 375  		} else {
	 376  			p.fmt.fmtInteger(v, 10, isSigned, verb, ldigits)
	 377  		}
	 378  	case 'd':
	 379  		p.fmt.fmtInteger(v, 10, isSigned, verb, ldigits)
	 380  	case 'b':
	 381  		p.fmt.fmtInteger(v, 2, isSigned, verb, ldigits)
	 382  	case 'o', 'O':
	 383  		p.fmt.fmtInteger(v, 8, isSigned, verb, ldigits)
	 384  	case 'x':
	 385  		p.fmt.fmtInteger(v, 16, isSigned, verb, ldigits)
	 386  	case 'X':
	 387  		p.fmt.fmtInteger(v, 16, isSigned, verb, udigits)
	 388  	case 'c':
	 389  		p.fmt.fmtC(v)
	 390  	case 'q':
	 391  		p.fmt.fmtQc(v)
	 392  	case 'U':
	 393  		p.fmt.fmtUnicode(v)
	 394  	default:
	 395  		p.badVerb(verb)
	 396  	}
	 397  }
	 398  
	 399  // fmtFloat formats a float. The default precision for each verb
	 400  // is specified as last argument in the call to fmt_float.
	 401  func (p *pp) fmtFloat(v float64, size int, verb rune) {
	 402  	switch verb {
	 403  	case 'v':
	 404  		p.fmt.fmtFloat(v, size, 'g', -1)
	 405  	case 'b', 'g', 'G', 'x', 'X':
	 406  		p.fmt.fmtFloat(v, size, verb, -1)
	 407  	case 'f', 'e', 'E':
	 408  		p.fmt.fmtFloat(v, size, verb, 6)
	 409  	case 'F':
	 410  		p.fmt.fmtFloat(v, size, 'f', 6)
	 411  	default:
	 412  		p.badVerb(verb)
	 413  	}
	 414  }
	 415  
	 416  // fmtComplex formats a complex number v with
	 417  // r = real(v) and j = imag(v) as (r+ji) using
	 418  // fmtFloat for r and j formatting.
	 419  func (p *pp) fmtComplex(v complex128, size int, verb rune) {
	 420  	// Make sure any unsupported verbs are found before the
	 421  	// calls to fmtFloat to not generate an incorrect error string.
	 422  	switch verb {
	 423  	case 'v', 'b', 'g', 'G', 'x', 'X', 'f', 'F', 'e', 'E':
	 424  		oldPlus := p.fmt.plus
	 425  		p.buf.writeByte('(')
	 426  		p.fmtFloat(real(v), size/2, verb)
	 427  		// Imaginary part always has a sign.
	 428  		p.fmt.plus = true
	 429  		p.fmtFloat(imag(v), size/2, verb)
	 430  		p.buf.writeString("i)")
	 431  		p.fmt.plus = oldPlus
	 432  	default:
	 433  		p.badVerb(verb)
	 434  	}
	 435  }
	 436  
	 437  func (p *pp) fmtString(v string, verb rune) {
	 438  	switch verb {
	 439  	case 'v':
	 440  		if p.fmt.sharpV {
	 441  			p.fmt.fmtQ(v)
	 442  		} else {
	 443  			p.fmt.fmtS(v)
	 444  		}
	 445  	case 's':
	 446  		p.fmt.fmtS(v)
	 447  	case 'x':
	 448  		p.fmt.fmtSx(v, ldigits)
	 449  	case 'X':
	 450  		p.fmt.fmtSx(v, udigits)
	 451  	case 'q':
	 452  		p.fmt.fmtQ(v)
	 453  	default:
	 454  		p.badVerb(verb)
	 455  	}
	 456  }
	 457  
	 458  func (p *pp) fmtBytes(v []byte, verb rune, typeString string) {
	 459  	switch verb {
	 460  	case 'v', 'd':
	 461  		if p.fmt.sharpV {
	 462  			p.buf.writeString(typeString)
	 463  			if v == nil {
	 464  				p.buf.writeString(nilParenString)
	 465  				return
	 466  			}
	 467  			p.buf.writeByte('{')
	 468  			for i, c := range v {
	 469  				if i > 0 {
	 470  					p.buf.writeString(commaSpaceString)
	 471  				}
	 472  				p.fmt0x64(uint64(c), true)
	 473  			}
	 474  			p.buf.writeByte('}')
	 475  		} else {
	 476  			p.buf.writeByte('[')
	 477  			for i, c := range v {
	 478  				if i > 0 {
	 479  					p.buf.writeByte(' ')
	 480  				}
	 481  				p.fmt.fmtInteger(uint64(c), 10, unsigned, verb, ldigits)
	 482  			}
	 483  			p.buf.writeByte(']')
	 484  		}
	 485  	case 's':
	 486  		p.fmt.fmtBs(v)
	 487  	case 'x':
	 488  		p.fmt.fmtBx(v, ldigits)
	 489  	case 'X':
	 490  		p.fmt.fmtBx(v, udigits)
	 491  	case 'q':
	 492  		p.fmt.fmtQ(string(v))
	 493  	default:
	 494  		p.printValue(reflect.ValueOf(v), verb, 0)
	 495  	}
	 496  }
	 497  
	 498  func (p *pp) fmtPointer(value reflect.Value, verb rune) {
	 499  	var u uintptr
	 500  	switch value.Kind() {
	 501  	case reflect.Chan, reflect.Func, reflect.Map, reflect.Ptr, reflect.Slice, reflect.UnsafePointer:
	 502  		u = value.Pointer()
	 503  	default:
	 504  		p.badVerb(verb)
	 505  		return
	 506  	}
	 507  
	 508  	switch verb {
	 509  	case 'v':
	 510  		if p.fmt.sharpV {
	 511  			p.buf.writeByte('(')
	 512  			p.buf.writeString(value.Type().String())
	 513  			p.buf.writeString(")(")
	 514  			if u == 0 {
	 515  				p.buf.writeString(nilString)
	 516  			} else {
	 517  				p.fmt0x64(uint64(u), true)
	 518  			}
	 519  			p.buf.writeByte(')')
	 520  		} else {
	 521  			if u == 0 {
	 522  				p.fmt.padString(nilAngleString)
	 523  			} else {
	 524  				p.fmt0x64(uint64(u), !p.fmt.sharp)
	 525  			}
	 526  		}
	 527  	case 'p':
	 528  		p.fmt0x64(uint64(u), !p.fmt.sharp)
	 529  	case 'b', 'o', 'd', 'x', 'X':
	 530  		p.fmtInteger(uint64(u), unsigned, verb)
	 531  	default:
	 532  		p.badVerb(verb)
	 533  	}
	 534  }
	 535  
	 536  func (p *pp) catchPanic(arg interface{}, verb rune, method string) {
	 537  	if err := recover(); err != nil {
	 538  		// If it's a nil pointer, just say "<nil>". The likeliest causes are a
	 539  		// Stringer that fails to guard against nil or a nil pointer for a
	 540  		// value receiver, and in either case, "<nil>" is a nice result.
	 541  		if v := reflect.ValueOf(arg); v.Kind() == reflect.Ptr && v.IsNil() {
	 542  			p.buf.writeString(nilAngleString)
	 543  			return
	 544  		}
	 545  		// Otherwise print a concise panic message. Most of the time the panic
	 546  		// value will print itself nicely.
	 547  		if p.panicking {
	 548  			// Nested panics; the recursion in printArg cannot succeed.
	 549  			panic(err)
	 550  		}
	 551  
	 552  		oldFlags := p.fmt.fmtFlags
	 553  		// For this output we want default behavior.
	 554  		p.fmt.clearflags()
	 555  
	 556  		p.buf.writeString(percentBangString)
	 557  		p.buf.writeRune(verb)
	 558  		p.buf.writeString(panicString)
	 559  		p.buf.writeString(method)
	 560  		p.buf.writeString(" method: ")
	 561  		p.panicking = true
	 562  		p.printArg(err, 'v')
	 563  		p.panicking = false
	 564  		p.buf.writeByte(')')
	 565  
	 566  		p.fmt.fmtFlags = oldFlags
	 567  	}
	 568  }
	 569  
	 570  func (p *pp) handleMethods(verb rune) (handled bool) {
	 571  	if p.erroring {
	 572  		return
	 573  	}
	 574  	if verb == 'w' {
	 575  		// It is invalid to use %w other than with Errorf, more than once,
	 576  		// or with a non-error arg.
	 577  		err, ok := p.arg.(error)
	 578  		if !ok || !p.wrapErrs || p.wrappedErr != nil {
	 579  			p.wrappedErr = nil
	 580  			p.wrapErrs = false
	 581  			p.badVerb(verb)
	 582  			return true
	 583  		}
	 584  		p.wrappedErr = err
	 585  		// If the arg is a Formatter, pass 'v' as the verb to it.
	 586  		verb = 'v'
	 587  	}
	 588  
	 589  	// Is it a Formatter?
	 590  	if formatter, ok := p.arg.(Formatter); ok {
	 591  		handled = true
	 592  		defer p.catchPanic(p.arg, verb, "Format")
	 593  		formatter.Format(p, verb)
	 594  		return
	 595  	}
	 596  
	 597  	// If we're doing Go syntax and the argument knows how to supply it, take care of it now.
	 598  	if p.fmt.sharpV {
	 599  		if stringer, ok := p.arg.(GoStringer); ok {
	 600  			handled = true
	 601  			defer p.catchPanic(p.arg, verb, "GoString")
	 602  			// Print the result of GoString unadorned.
	 603  			p.fmt.fmtS(stringer.GoString())
	 604  			return
	 605  		}
	 606  	} else {
	 607  		// If a string is acceptable according to the format, see if
	 608  		// the value satisfies one of the string-valued interfaces.
	 609  		// Println etc. set verb to %v, which is "stringable".
	 610  		switch verb {
	 611  		case 'v', 's', 'x', 'X', 'q':
	 612  			// Is it an error or Stringer?
	 613  			// The duplication in the bodies is necessary:
	 614  			// setting handled and deferring catchPanic
	 615  			// must happen before calling the method.
	 616  			switch v := p.arg.(type) {
	 617  			case error:
	 618  				handled = true
	 619  				defer p.catchPanic(p.arg, verb, "Error")
	 620  				p.fmtString(v.Error(), verb)
	 621  				return
	 622  
	 623  			case Stringer:
	 624  				handled = true
	 625  				defer p.catchPanic(p.arg, verb, "String")
	 626  				p.fmtString(v.String(), verb)
	 627  				return
	 628  			}
	 629  		}
	 630  	}
	 631  	return false
	 632  }
	 633  
	 634  func (p *pp) printArg(arg interface{}, verb rune) {
	 635  	p.arg = arg
	 636  	p.value = reflect.Value{}
	 637  
	 638  	if arg == nil {
	 639  		switch verb {
	 640  		case 'T', 'v':
	 641  			p.fmt.padString(nilAngleString)
	 642  		default:
	 643  			p.badVerb(verb)
	 644  		}
	 645  		return
	 646  	}
	 647  
	 648  	// Special processing considerations.
	 649  	// %T (the value's type) and %p (its address) are special; we always do them first.
	 650  	switch verb {
	 651  	case 'T':
	 652  		p.fmt.fmtS(reflect.TypeOf(arg).String())
	 653  		return
	 654  	case 'p':
	 655  		p.fmtPointer(reflect.ValueOf(arg), 'p')
	 656  		return
	 657  	}
	 658  
	 659  	// Some types can be done without reflection.
	 660  	switch f := arg.(type) {
	 661  	case bool:
	 662  		p.fmtBool(f, verb)
	 663  	case float32:
	 664  		p.fmtFloat(float64(f), 32, verb)
	 665  	case float64:
	 666  		p.fmtFloat(f, 64, verb)
	 667  	case complex64:
	 668  		p.fmtComplex(complex128(f), 64, verb)
	 669  	case complex128:
	 670  		p.fmtComplex(f, 128, verb)
	 671  	case int:
	 672  		p.fmtInteger(uint64(f), signed, verb)
	 673  	case int8:
	 674  		p.fmtInteger(uint64(f), signed, verb)
	 675  	case int16:
	 676  		p.fmtInteger(uint64(f), signed, verb)
	 677  	case int32:
	 678  		p.fmtInteger(uint64(f), signed, verb)
	 679  	case int64:
	 680  		p.fmtInteger(uint64(f), signed, verb)
	 681  	case uint:
	 682  		p.fmtInteger(uint64(f), unsigned, verb)
	 683  	case uint8:
	 684  		p.fmtInteger(uint64(f), unsigned, verb)
	 685  	case uint16:
	 686  		p.fmtInteger(uint64(f), unsigned, verb)
	 687  	case uint32:
	 688  		p.fmtInteger(uint64(f), unsigned, verb)
	 689  	case uint64:
	 690  		p.fmtInteger(f, unsigned, verb)
	 691  	case uintptr:
	 692  		p.fmtInteger(uint64(f), unsigned, verb)
	 693  	case string:
	 694  		p.fmtString(f, verb)
	 695  	case []byte:
	 696  		p.fmtBytes(f, verb, "[]byte")
	 697  	case reflect.Value:
	 698  		// Handle extractable values with special methods
	 699  		// since printValue does not handle them at depth 0.
	 700  		if f.IsValid() && f.CanInterface() {
	 701  			p.arg = f.Interface()
	 702  			if p.handleMethods(verb) {
	 703  				return
	 704  			}
	 705  		}
	 706  		p.printValue(f, verb, 0)
	 707  	default:
	 708  		// If the type is not simple, it might have methods.
	 709  		if !p.handleMethods(verb) {
	 710  			// Need to use reflection, since the type had no
	 711  			// interface methods that could be used for formatting.
	 712  			p.printValue(reflect.ValueOf(f), verb, 0)
	 713  		}
	 714  	}
	 715  }
	 716  
	 717  // printValue is similar to printArg but starts with a reflect value, not an interface{} value.
	 718  // It does not handle 'p' and 'T' verbs because these should have been already handled by printArg.
	 719  func (p *pp) printValue(value reflect.Value, verb rune, depth int) {
	 720  	// Handle values with special methods if not already handled by printArg (depth == 0).
	 721  	if depth > 0 && value.IsValid() && value.CanInterface() {
	 722  		p.arg = value.Interface()
	 723  		if p.handleMethods(verb) {
	 724  			return
	 725  		}
	 726  	}
	 727  	p.arg = nil
	 728  	p.value = value
	 729  
	 730  	switch f := value; value.Kind() {
	 731  	case reflect.Invalid:
	 732  		if depth == 0 {
	 733  			p.buf.writeString(invReflectString)
	 734  		} else {
	 735  			switch verb {
	 736  			case 'v':
	 737  				p.buf.writeString(nilAngleString)
	 738  			default:
	 739  				p.badVerb(verb)
	 740  			}
	 741  		}
	 742  	case reflect.Bool:
	 743  		p.fmtBool(f.Bool(), verb)
	 744  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
	 745  		p.fmtInteger(uint64(f.Int()), signed, verb)
	 746  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
	 747  		p.fmtInteger(f.Uint(), unsigned, verb)
	 748  	case reflect.Float32:
	 749  		p.fmtFloat(f.Float(), 32, verb)
	 750  	case reflect.Float64:
	 751  		p.fmtFloat(f.Float(), 64, verb)
	 752  	case reflect.Complex64:
	 753  		p.fmtComplex(f.Complex(), 64, verb)
	 754  	case reflect.Complex128:
	 755  		p.fmtComplex(f.Complex(), 128, verb)
	 756  	case reflect.String:
	 757  		p.fmtString(f.String(), verb)
	 758  	case reflect.Map:
	 759  		if p.fmt.sharpV {
	 760  			p.buf.writeString(f.Type().String())
	 761  			if f.IsNil() {
	 762  				p.buf.writeString(nilParenString)
	 763  				return
	 764  			}
	 765  			p.buf.writeByte('{')
	 766  		} else {
	 767  			p.buf.writeString(mapString)
	 768  		}
	 769  		sorted := fmtsort.Sort(f)
	 770  		for i, key := range sorted.Key {
	 771  			if i > 0 {
	 772  				if p.fmt.sharpV {
	 773  					p.buf.writeString(commaSpaceString)
	 774  				} else {
	 775  					p.buf.writeByte(' ')
	 776  				}
	 777  			}
	 778  			p.printValue(key, verb, depth+1)
	 779  			p.buf.writeByte(':')
	 780  			p.printValue(sorted.Value[i], verb, depth+1)
	 781  		}
	 782  		if p.fmt.sharpV {
	 783  			p.buf.writeByte('}')
	 784  		} else {
	 785  			p.buf.writeByte(']')
	 786  		}
	 787  	case reflect.Struct:
	 788  		if p.fmt.sharpV {
	 789  			p.buf.writeString(f.Type().String())
	 790  		}
	 791  		p.buf.writeByte('{')
	 792  		for i := 0; i < f.NumField(); i++ {
	 793  			if i > 0 {
	 794  				if p.fmt.sharpV {
	 795  					p.buf.writeString(commaSpaceString)
	 796  				} else {
	 797  					p.buf.writeByte(' ')
	 798  				}
	 799  			}
	 800  			if p.fmt.plusV || p.fmt.sharpV {
	 801  				if name := f.Type().Field(i).Name; name != "" {
	 802  					p.buf.writeString(name)
	 803  					p.buf.writeByte(':')
	 804  				}
	 805  			}
	 806  			p.printValue(getField(f, i), verb, depth+1)
	 807  		}
	 808  		p.buf.writeByte('}')
	 809  	case reflect.Interface:
	 810  		value := f.Elem()
	 811  		if !value.IsValid() {
	 812  			if p.fmt.sharpV {
	 813  				p.buf.writeString(f.Type().String())
	 814  				p.buf.writeString(nilParenString)
	 815  			} else {
	 816  				p.buf.writeString(nilAngleString)
	 817  			}
	 818  		} else {
	 819  			p.printValue(value, verb, depth+1)
	 820  		}
	 821  	case reflect.Array, reflect.Slice:
	 822  		switch verb {
	 823  		case 's', 'q', 'x', 'X':
	 824  			// Handle byte and uint8 slices and arrays special for the above verbs.
	 825  			t := f.Type()
	 826  			if t.Elem().Kind() == reflect.Uint8 {
	 827  				var bytes []byte
	 828  				if f.Kind() == reflect.Slice {
	 829  					bytes = f.Bytes()
	 830  				} else if f.CanAddr() {
	 831  					bytes = f.Slice(0, f.Len()).Bytes()
	 832  				} else {
	 833  					// We have an array, but we cannot Slice() a non-addressable array,
	 834  					// so we build a slice by hand. This is a rare case but it would be nice
	 835  					// if reflection could help a little more.
	 836  					bytes = make([]byte, f.Len())
	 837  					for i := range bytes {
	 838  						bytes[i] = byte(f.Index(i).Uint())
	 839  					}
	 840  				}
	 841  				p.fmtBytes(bytes, verb, t.String())
	 842  				return
	 843  			}
	 844  		}
	 845  		if p.fmt.sharpV {
	 846  			p.buf.writeString(f.Type().String())
	 847  			if f.Kind() == reflect.Slice && f.IsNil() {
	 848  				p.buf.writeString(nilParenString)
	 849  				return
	 850  			}
	 851  			p.buf.writeByte('{')
	 852  			for i := 0; i < f.Len(); i++ {
	 853  				if i > 0 {
	 854  					p.buf.writeString(commaSpaceString)
	 855  				}
	 856  				p.printValue(f.Index(i), verb, depth+1)
	 857  			}
	 858  			p.buf.writeByte('}')
	 859  		} else {
	 860  			p.buf.writeByte('[')
	 861  			for i := 0; i < f.Len(); i++ {
	 862  				if i > 0 {
	 863  					p.buf.writeByte(' ')
	 864  				}
	 865  				p.printValue(f.Index(i), verb, depth+1)
	 866  			}
	 867  			p.buf.writeByte(']')
	 868  		}
	 869  	case reflect.Ptr:
	 870  		// pointer to array or slice or struct? ok at top level
	 871  		// but not embedded (avoid loops)
	 872  		if depth == 0 && f.Pointer() != 0 {
	 873  			switch a := f.Elem(); a.Kind() {
	 874  			case reflect.Array, reflect.Slice, reflect.Struct, reflect.Map:
	 875  				p.buf.writeByte('&')
	 876  				p.printValue(a, verb, depth+1)
	 877  				return
	 878  			}
	 879  		}
	 880  		fallthrough
	 881  	case reflect.Chan, reflect.Func, reflect.UnsafePointer:
	 882  		p.fmtPointer(f, verb)
	 883  	default:
	 884  		p.unknownType(f)
	 885  	}
	 886  }
	 887  
	 888  // intFromArg gets the argNumth element of a. On return, isInt reports whether the argument has integer type.
	 889  func intFromArg(a []interface{}, argNum int) (num int, isInt bool, newArgNum int) {
	 890  	newArgNum = argNum
	 891  	if argNum < len(a) {
	 892  		num, isInt = a[argNum].(int) // Almost always OK.
	 893  		if !isInt {
	 894  			// Work harder.
	 895  			switch v := reflect.ValueOf(a[argNum]); v.Kind() {
	 896  			case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
	 897  				n := v.Int()
	 898  				if int64(int(n)) == n {
	 899  					num = int(n)
	 900  					isInt = true
	 901  				}
	 902  			case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
	 903  				n := v.Uint()
	 904  				if int64(n) >= 0 && uint64(int(n)) == n {
	 905  					num = int(n)
	 906  					isInt = true
	 907  				}
	 908  			default:
	 909  				// Already 0, false.
	 910  			}
	 911  		}
	 912  		newArgNum = argNum + 1
	 913  		if tooLarge(num) {
	 914  			num = 0
	 915  			isInt = false
	 916  		}
	 917  	}
	 918  	return
	 919  }
	 920  
	 921  // parseArgNumber returns the value of the bracketed number, minus 1
	 922  // (explicit argument numbers are one-indexed but we want zero-indexed).
	 923  // The opening bracket is known to be present at format[0].
	 924  // The returned values are the index, the number of bytes to consume
	 925  // up to the closing paren, if present, and whether the number parsed
	 926  // ok. The bytes to consume will be 1 if no closing paren is present.
	 927  func parseArgNumber(format string) (index int, wid int, ok bool) {
	 928  	// There must be at least 3 bytes: [n].
	 929  	if len(format) < 3 {
	 930  		return 0, 1, false
	 931  	}
	 932  
	 933  	// Find closing bracket.
	 934  	for i := 1; i < len(format); i++ {
	 935  		if format[i] == ']' {
	 936  			width, ok, newi := parsenum(format, 1, i)
	 937  			if !ok || newi != i {
	 938  				return 0, i + 1, false
	 939  			}
	 940  			return width - 1, i + 1, true // arg numbers are one-indexed and skip paren.
	 941  		}
	 942  	}
	 943  	return 0, 1, false
	 944  }
	 945  
	 946  // argNumber returns the next argument to evaluate, which is either the value of the passed-in
	 947  // argNum or the value of the bracketed integer that begins format[i:]. It also returns
	 948  // the new value of i, that is, the index of the next byte of the format to process.
	 949  func (p *pp) argNumber(argNum int, format string, i int, numArgs int) (newArgNum, newi int, found bool) {
	 950  	if len(format) <= i || format[i] != '[' {
	 951  		return argNum, i, false
	 952  	}
	 953  	p.reordered = true
	 954  	index, wid, ok := parseArgNumber(format[i:])
	 955  	if ok && 0 <= index && index < numArgs {
	 956  		return index, i + wid, true
	 957  	}
	 958  	p.goodArgNum = false
	 959  	return argNum, i + wid, ok
	 960  }
	 961  
	 962  func (p *pp) badArgNum(verb rune) {
	 963  	p.buf.writeString(percentBangString)
	 964  	p.buf.writeRune(verb)
	 965  	p.buf.writeString(badIndexString)
	 966  }
	 967  
	 968  func (p *pp) missingArg(verb rune) {
	 969  	p.buf.writeString(percentBangString)
	 970  	p.buf.writeRune(verb)
	 971  	p.buf.writeString(missingString)
	 972  }
	 973  
	 974  func (p *pp) doPrintf(format string, a []interface{}) {
	 975  	end := len(format)
	 976  	argNum := 0				 // we process one argument per non-trivial format
	 977  	afterIndex := false // previous item in format was an index like [3].
	 978  	p.reordered = false
	 979  formatLoop:
	 980  	for i := 0; i < end; {
	 981  		p.goodArgNum = true
	 982  		lasti := i
	 983  		for i < end && format[i] != '%' {
	 984  			i++
	 985  		}
	 986  		if i > lasti {
	 987  			p.buf.writeString(format[lasti:i])
	 988  		}
	 989  		if i >= end {
	 990  			// done processing format string
	 991  			break
	 992  		}
	 993  
	 994  		// Process one verb
	 995  		i++
	 996  
	 997  		// Do we have flags?
	 998  		p.fmt.clearflags()
	 999  	simpleFormat:
	1000  		for ; i < end; i++ {
	1001  			c := format[i]
	1002  			switch c {
	1003  			case '#':
	1004  				p.fmt.sharp = true
	1005  			case '0':
	1006  				p.fmt.zero = !p.fmt.minus // Only allow zero padding to the left.
	1007  			case '+':
	1008  				p.fmt.plus = true
	1009  			case '-':
	1010  				p.fmt.minus = true
	1011  				p.fmt.zero = false // Do not pad with zeros to the right.
	1012  			case ' ':
	1013  				p.fmt.space = true
	1014  			default:
	1015  				// Fast path for common case of ascii lower case simple verbs
	1016  				// without precision or width or argument indices.
	1017  				if 'a' <= c && c <= 'z' && argNum < len(a) {
	1018  					if c == 'v' {
	1019  						// Go syntax
	1020  						p.fmt.sharpV = p.fmt.sharp
	1021  						p.fmt.sharp = false
	1022  						// Struct-field syntax
	1023  						p.fmt.plusV = p.fmt.plus
	1024  						p.fmt.plus = false
	1025  					}
	1026  					p.printArg(a[argNum], rune(c))
	1027  					argNum++
	1028  					i++
	1029  					continue formatLoop
	1030  				}
	1031  				// Format is more complex than simple flags and a verb or is malformed.
	1032  				break simpleFormat
	1033  			}
	1034  		}
	1035  
	1036  		// Do we have an explicit argument index?
	1037  		argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
	1038  
	1039  		// Do we have width?
	1040  		if i < end && format[i] == '*' {
	1041  			i++
	1042  			p.fmt.wid, p.fmt.widPresent, argNum = intFromArg(a, argNum)
	1043  
	1044  			if !p.fmt.widPresent {
	1045  				p.buf.writeString(badWidthString)
	1046  			}
	1047  
	1048  			// We have a negative width, so take its value and ensure
	1049  			// that the minus flag is set
	1050  			if p.fmt.wid < 0 {
	1051  				p.fmt.wid = -p.fmt.wid
	1052  				p.fmt.minus = true
	1053  				p.fmt.zero = false // Do not pad with zeros to the right.
	1054  			}
	1055  			afterIndex = false
	1056  		} else {
	1057  			p.fmt.wid, p.fmt.widPresent, i = parsenum(format, i, end)
	1058  			if afterIndex && p.fmt.widPresent { // "%[3]2d"
	1059  				p.goodArgNum = false
	1060  			}
	1061  		}
	1062  
	1063  		// Do we have precision?
	1064  		if i+1 < end && format[i] == '.' {
	1065  			i++
	1066  			if afterIndex { // "%[3].2d"
	1067  				p.goodArgNum = false
	1068  			}
	1069  			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
	1070  			if i < end && format[i] == '*' {
	1071  				i++
	1072  				p.fmt.prec, p.fmt.precPresent, argNum = intFromArg(a, argNum)
	1073  				// Negative precision arguments don't make sense
	1074  				if p.fmt.prec < 0 {
	1075  					p.fmt.prec = 0
	1076  					p.fmt.precPresent = false
	1077  				}
	1078  				if !p.fmt.precPresent {
	1079  					p.buf.writeString(badPrecString)
	1080  				}
	1081  				afterIndex = false
	1082  			} else {
	1083  				p.fmt.prec, p.fmt.precPresent, i = parsenum(format, i, end)
	1084  				if !p.fmt.precPresent {
	1085  					p.fmt.prec = 0
	1086  					p.fmt.precPresent = true
	1087  				}
	1088  			}
	1089  		}
	1090  
	1091  		if !afterIndex {
	1092  			argNum, i, afterIndex = p.argNumber(argNum, format, i, len(a))
	1093  		}
	1094  
	1095  		if i >= end {
	1096  			p.buf.writeString(noVerbString)
	1097  			break
	1098  		}
	1099  
	1100  		verb, size := rune(format[i]), 1
	1101  		if verb >= utf8.RuneSelf {
	1102  			verb, size = utf8.DecodeRuneInString(format[i:])
	1103  		}
	1104  		i += size
	1105  
	1106  		switch {
	1107  		case verb == '%': // Percent does not absorb operands and ignores f.wid and f.prec.
	1108  			p.buf.writeByte('%')
	1109  		case !p.goodArgNum:
	1110  			p.badArgNum(verb)
	1111  		case argNum >= len(a): // No argument left over to print for the current verb.
	1112  			p.missingArg(verb)
	1113  		case verb == 'v':
	1114  			// Go syntax
	1115  			p.fmt.sharpV = p.fmt.sharp
	1116  			p.fmt.sharp = false
	1117  			// Struct-field syntax
	1118  			p.fmt.plusV = p.fmt.plus
	1119  			p.fmt.plus = false
	1120  			fallthrough
	1121  		default:
	1122  			p.printArg(a[argNum], verb)
	1123  			argNum++
	1124  		}
	1125  	}
	1126  
	1127  	// Check for extra arguments unless the call accessed the arguments
	1128  	// out of order, in which case it's too expensive to detect if they've all
	1129  	// been used and arguably OK if they're not.
	1130  	if !p.reordered && argNum < len(a) {
	1131  		p.fmt.clearflags()
	1132  		p.buf.writeString(extraString)
	1133  		for i, arg := range a[argNum:] {
	1134  			if i > 0 {
	1135  				p.buf.writeString(commaSpaceString)
	1136  			}
	1137  			if arg == nil {
	1138  				p.buf.writeString(nilAngleString)
	1139  			} else {
	1140  				p.buf.writeString(reflect.TypeOf(arg).String())
	1141  				p.buf.writeByte('=')
	1142  				p.printArg(arg, 'v')
	1143  			}
	1144  		}
	1145  		p.buf.writeByte(')')
	1146  	}
	1147  }
	1148  
	1149  func (p *pp) doPrint(a []interface{}) {
	1150  	prevString := false
	1151  	for argNum, arg := range a {
	1152  		isString := arg != nil && reflect.TypeOf(arg).Kind() == reflect.String
	1153  		// Add a space between two non-string arguments.
	1154  		if argNum > 0 && !isString && !prevString {
	1155  			p.buf.writeByte(' ')
	1156  		}
	1157  		p.printArg(arg, 'v')
	1158  		prevString = isString
	1159  	}
	1160  }
	1161  
	1162  // doPrintln is like doPrint but always adds a space between arguments
	1163  // and a newline after the last argument.
	1164  func (p *pp) doPrintln(a []interface{}) {
	1165  	for argNum, arg := range a {
	1166  		if argNum > 0 {
	1167  			p.buf.writeByte(' ')
	1168  		}
	1169  		p.printArg(arg, 'v')
	1170  	}
	1171  	p.buf.writeByte('\n')
	1172  }
	1173  

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