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PRINTF(3)	       FreeBSD Library Functions Manual		     PRINTF(3)

NAME
     printf, fprintf, sprintf, snprintf, asprintf, dprintf, vprintf, vfprintf,
     vsprintf, vsnprintf, vasprintf, vdprintf -- formatted output conversion

LIBRARY
     Standard C	Library	(libc, -lc)

SYNOPSIS
     #define _WITH_DPRINTF
     #include <stdio.h>

     int
     printf(const char * restrict format, ...);

     int
     fprintf(FILE * restrict stream, const char	* restrict format, ...);

     int
     sprintf(char * restrict str, const	char * restrict	format,	...);

     int
     snprintf(char * restrict str, size_t size,	const char * restrict format,
	 ...);

     int
     asprintf(char **ret, const	char *format, ...);

     int
     dprintf(int fd, const char	* restrict format, ...);

     #include <stdarg.h>

     int
     vprintf(const char	* restrict format, va_list ap);

     int
     vfprintf(FILE * restrict stream, const char * restrict format,
	 va_list ap);

     int
     vsprintf(char * restrict str, const char *	restrict format, va_list ap);

     int
     vsnprintf(char * restrict str, size_t size, const char * restrict format,
	 va_list ap);

     int
     vasprintf(char **ret, const char *format, va_list ap);

     int
     vdprintf(int fd, const char * restrict format, va_list ap);

DESCRIPTION
     The printf() family of functions produces output according	to a format as
     described below.  The printf() and	vprintf() functions write output to
     stdout, the standard output stream; fprintf() and vfprintf() write	output
     to	the given output stream; dprintf() and vdprintf() write	output to the
     given file	descriptor; sprintf(), snprintf(), vsprintf(), and vsnprintf()
     write to the character string str;	and asprintf() and vasprintf() dynami-
     cally allocate a new string with malloc(3).

     These functions write the output under the	control	of a format string
     that specifies how	subsequent arguments (or arguments accessed via	the
     variable-length argument facilities of stdarg(3)) are converted for out-
     put.

     These functions return the	number of characters printed (not including
     the trailing `\0' used to end output to strings) or a negative value if
     an	output error occurs, except for	snprintf() and vsnprintf(), which
     return the	number of characters that would	have been printed if the size
     were unlimited (again, not	including the final `\0').

     The asprintf() and	vasprintf() functions set *ret to be a pointer to a
     buffer sufficiently large to hold the formatted string.  This pointer
     should be passed to free(3) to release the	allocated storage when it is
     no	longer needed.	If sufficient space cannot be allocated, asprintf()
     and vasprintf() will return -1 and	set ret	to be a	NULL pointer.

     The snprintf() and	vsnprintf() functions will write at most size-1	of the
     characters	printed	into the output	string (the size'th character then
     gets the terminating `\0'); if the	return value is	greater	than or	equal
     to	the size argument, the string was too short and	some of	the printed
     characters	were discarded.	 The output is always null-terminated.

     The sprintf() and vsprintf() functions effectively	assume an infinite
     size.

     The format	string is composed of zero or more directives: ordinary	char-
     acters (not %), which are copied unchanged	to the output stream; and con-
     version specifications, each of which results in fetching zero or more
     subsequent	arguments.  Each conversion specification is introduced	by the
     % character.  The arguments must correspond properly (after type promo-
     tion) with	the conversion specifier.  After the %,	the following appear
     in	sequence:

     +o	 An optional field, consisting of a decimal digit string followed by a
	 $, specifying the next	argument to access.  If	this field is not pro-
	 vided,	the argument following the last	argument accessed will be
	 used.	Arguments are numbered starting	at 1.  If unaccessed arguments
	 in the	format string are interspersed with ones that are accessed the
	 results will be indeterminate.

     +o	 Zero or more of the following flags:

	 `#'	      The value	should be converted to an ``alternate form''.
		      For c, d,	i, n, p, s, and	u conversions, this option has
		      no effect.  For o	conversions, the precision of the num-
		      ber is increased to force	the first character of the
		      output string to a zero.	For x and X conversions, a
		      non-zero result has the string `0x' (or `0X' for X con-
		      versions)	prepended to it.  For a, A, e, E, f, F,	g, and
		      G	conversions, the result	will always contain a decimal
		      point, even if no	digits follow it (normally, a decimal
		      point appears in the results of those conversions	only
		      if a digit follows).  For	g and G	conversions, trailing
		      zeros are	not removed from the result as they would oth-
		      erwise be.

	 `0' (zero)   Zero padding.  For all conversions except	n, the con-
		      verted value is padded on	the left with zeros rather
		      than blanks.  If a precision is given with a numeric
		      conversion (d, i,	o, u, i, x, and	X), the	0 flag is
		      ignored.

	 `-'	      A	negative field width flag; the converted value is to
		      be left adjusted on the field boundary.  Except for n
		      conversions, the converted value is padded on the	right
		      with blanks, rather than on the left with	blanks or
		      zeros.  A	- overrides a 0	if both	are given.

	 ` ' (space)  A	blank should be	left before a positive number produced
		      by a signed conversion (a, A, d, e, E, f,	F, g, G, or
		      i).

	 `+'	      A	sign must always be placed before a number produced by
		      a	signed conversion.  A +	overrides a space if both are
		      used.

	 `'' (apostrophe)
		      Decimal conversions (d, u, or i) or the integral portion
		      of a floating point conversion (f	or F) should be
		      grouped and separated by thousands using the non-mone-
		      tary separator returned by localeconv(3).

     +o	 An optional decimal digit string specifying a minimum field width.
	 If the	converted value	has fewer characters than the field width, it
	 will be padded	with spaces on the left	(or right, if the left-adjust-
	 ment flag has been given) to fill out the field width.

     +o	 An optional precision,	in the form of a period	. followed by an
	 optional digit	string.	 If the	digit string is	omitted, the precision
	 is taken as zero.  This gives the minimum number of digits to appear
	 for d,	i, o, u, x, and	X conversions, the number of digits to appear
	 after the decimal-point for a,	A, e, E, f, and	F conversions, the
	 maximum number	of significant digits for g and	G conversions, or the
	 maximum number	of characters to be printed from a string for s	con-
	 versions.

     +o	 An optional length modifier, that specifies the size of the argument.
	 The following length modifiers	are valid for the d, i,	n, o, u, x, or
	 X conversion:

	 Modifier	   d, i		  o, u,	x, X		n
	 hh		   signed char	  unsigned char		signed char *
	 h		   short	  unsigned short	short *
	 l (ell)	   long		  unsigned long		long *
	 ll (ell ell)	   long	long	  unsigned long	long	long long *
	 j		   intmax_t	  uintmax_t		intmax_t *
	 t		   ptrdiff_t	  (see note)		ptrdiff_t *
	 z		   (see	note)	  size_t		(see note)
	 q (deprecated)	   quad_t	  u_quad_t		quad_t *

	 Note: the t modifier, when applied to a o, u, x, or X conversion,
	 indicates that	the argument is	of an unsigned type equivalent in size
	 to a ptrdiff_t.  The z	modifier, when applied to a d or i conversion,
	 indicates that	the argument is	of a signed type equivalent in size to
	 a size_t.  Similarly, when applied to an n conversion,	it indicates
	 that the argument is a	pointer	to a signed type equivalent in size to
	 a size_t.

	 The following length modifier is valid	for the	a, A, e, E, f, F, g,
	 or G conversion:

	 Modifier    a,	A, e, E, f, F, g, G
	 l (ell)     double (ignored, same behavior as without it)
	 L	     long double

	 The following length modifier is valid	for the	c or s conversion:

	 Modifier    c	       s
	 l (ell)     wint_t    wchar_t *

     +o	 A character that specifies the	type of	conversion to be applied.

     A field width or precision, or both, may be indicated by an asterisk `*'
     or	an asterisk followed by	one or more decimal digits and a `$' instead
     of	a digit	string.	 In this case, an int argument supplies	the field
     width or precision.  A negative field width is treated as a left adjust-
     ment flag followed	by a positive field width; a negative precision	is
     treated as	though it were missing.	 If a single format directive mixes
     positional	(nn$) and non-positional arguments, the	results	are undefined.

     The conversion specifiers and their meanings are:

     diouxX  The int (or appropriate variant) argument is converted to signed
	     decimal (d	and i),	unsigned octal (o), unsigned decimal (u), or
	     unsigned hexadecimal (x and X) notation.  The letters ``abcdef''
	     are used for x conversions; the letters ``ABCDEF''	are used for X
	     conversions.  The precision, if any, gives	the minimum number of
	     digits that must appear; if the converted value requires fewer
	     digits, it	is padded on the left with zeros.

     DOU     The long int argument is converted	to signed decimal, unsigned
	     octal, or unsigned	decimal, as if the format had been ld, lo, or
	     lu	respectively.  These conversion	characters are deprecated, and
	     will eventually disappear.

     eE	     The double	argument is rounded and	converted in the style
	     [-]d.ddde+-dd where there is one digit before the decimal-point
	     character and the number of digits	after it is equal to the pre-
	     cision; if	the precision is missing, it is	taken as 6; if the
	     precision is zero,	no decimal-point character appears.  An	E con-
	     version uses the letter `E' (rather than `e') to introduce	the
	     exponent.	The exponent always contains at	least two digits; if
	     the value is zero,	the exponent is	00.

	     For a, A, e, E, f,	F, g, and G conversions, positive and negative
	     infinity are represented as inf and -inf respectively when	using
	     the lowercase conversion character, and INF and -INF respectively
	     when using	the uppercase conversion character.  Similarly,	NaN is
	     represented as nan	when using the lowercase conversion, and NAN
	     when using	the uppercase conversion.

     fF	     The double	argument is rounded and	converted to decimal notation
	     in	the style [-]ddd.ddd, where the	number of digits after the
	     decimal-point character is	equal to the precision specification.
	     If	the precision is missing, it is	taken as 6; if the precision
	     is	explicitly zero, no decimal-point character appears.  If a
	     decimal point appears, at least one digit appears before it.

     gG	     The double	argument is converted in style f or e (or F or E for G
	     conversions).  The	precision specifies the	number of significant
	     digits.  If the precision is missing, 6 digits are	given; if the
	     precision is zero,	it is treated as 1.  Style e is	used if	the
	     exponent from its conversion is less than -4 or greater than or
	     equal to the precision.  Trailing zeros are removed from the
	     fractional	part of	the result; a decimal point appears only if it
	     is	followed by at least one digit.

     aA	     The double	argument is rounded and	converted to hexadecimal nota-
	     tion in the style [-]0xh.hhhp[+-]d, where the number of digits
	     after the hexadecimal-point character is equal to the precision
	     specification.  If	the precision is missing, it is	taken as
	     enough to represent the floating-point number exactly, and	no
	     rounding occurs.  If the precision	is zero, no hexadecimal-point
	     character appears.	 The p is a literal character `p', and the
	     exponent consists of a positive or	negative sign followed by a
	     decimal number representing an exponent of	2.  The	A conversion
	     uses the prefix ``0X'' (rather than ``0x''), the letters
	     ``ABCDEF''	(rather	than ``abcdef'') to represent the hex digits,
	     and the letter `P'	(rather	than `p') to separate the mantissa and
	     exponent.

	     Note that there may be multiple valid ways	to represent floating-
	     point numbers in this hexadecimal format.	For example,
	     0x1.92p+1,	0x3.24p+0, 0x6.48p-1, and 0xc.9p-2 are all equivalent.
	     FreeBSD 8.0 and later always prints finite	non-zero numbers using
	     `1' as the	digit before the hexadecimal point.  Zeroes are	always
	     represented with a	mantissa of 0 (preceded	by a `-' if appropri-
	     ate) and an exponent of +0.

     C	     Treated as	c with the l (ell) modifier.

     c	     The int argument is converted to an unsigned char,	and the
	     resulting character is written.

	     If	the l (ell) modifier is	used, the wint_t argument shall	be
	     converted to a wchar_t, and the (potentially multi-byte) sequence
	     representing the single wide character is written,	including any
	     shift sequences.  If a shift sequence is used, the	shift state is
	     also restored to the original state after the character.

     S	     Treated as	s with the l (ell) modifier.

     s	     The char *	argument is expected to	be a pointer to	an array of
	     character type (pointer to	a string).  Characters from the	array
	     are written up to (but not	including) a terminating NUL charac-
	     ter; if a precision is specified, no more than the	number speci-
	     fied are written.	If a precision is given, no null character
	     need be present; if the precision is not specified, or is greater
	     than the size of the array, the array must	contain	a terminating
	     NUL character.

	     If	the l (ell) modifier is	used, the wchar_t * argument is
	     expected to be a pointer to an array of wide characters (pointer
	     to	a wide string).	 For each wide character in the	string,	the
	     (potentially multi-byte) sequence representing the	wide character
	     is	written, including any shift sequences.	 If any	shift sequence
	     is	used, the shift	state is also restored to the original state
	     after the string.	Wide characters	from the array are written up
	     to	(but not including) a terminating wide NUL character; if a
	     precision is specified, no	more than the number of	bytes speci-
	     fied are written (including shift sequences).  Partial characters
	     are never written.	 If a precision	is given, no null character
	     need be present; if the precision is not specified, or is greater
	     than the number of	bytes required to render the multibyte repre-
	     sentation of the string, the array	must contain a terminating
	     wide NUL character.

     p	     The void *	pointer	argument is printed in hexadecimal (as if by
	     `%#x' or `%#lx').

     n	     The number	of characters written so far is	stored into the	inte-
	     ger indicated by the int *	(or variant) pointer argument.	No
	     argument is converted.

     %	     A `%' is written.	No argument is converted.  The complete	con-
	     version specification is `%%'.

     The decimal point character is defined in the program's locale (category
     LC_NUMERIC).

     In	no case	does a non-existent or small field width cause truncation of a
     numeric field; if the result of a conversion is wider than	the field
     width, the	field is expanded to contain the conversion result.

EXAMPLES
     To	print a	date and time in the form ``Sunday, July 3, 10:02'', where
     weekday and month are pointers to strings:

	   #include <stdio.h>
	   fprintf(stdout, "%s,	%s %d, %.2d:%.2d\n",
		   weekday, month, day,	hour, min);

     To	print pi to five decimal places:

	   #include <math.h>
	   #include <stdio.h>
	   fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));

     To	allocate a 128 byte string and print into it:

	   #include <stdio.h>
	   #include <stdlib.h>
	   #include <stdarg.h>
	   char	*newfmt(const char *fmt, ...)
	   {
		   char	*p;
		   va_list ap;
		   if ((p = malloc(128)) == NULL)
			   return (NULL);
		   va_start(ap,	fmt);
		   (void) vsnprintf(p, 128, fmt, ap);
		   va_end(ap);
		   return (p);
	   }

COMPATIBILITY
     Many application writers used the name dprintf before the dprintf() func-
     tion was introduced in IEEE Std 1003.1 (``POSIX.1''), so a	prototype is
     not provided by default in	order to avoid compatibility problems.	Appli-
     cations that wish to use the dprintf() function described herein should
     either request a strict IEEE Std 1003.1-2008 (``POSIX.1'')	environment by
     defining the macro	_POSIX_C_SOURCE	to the value 200809 or greater,	or by
     defining the macro	_WITH_DPRINTF, prior to	the inclusion of <stdio.h>.
     For compatibility with GNU	libc, defining either _BSD_SOURCE or
     _GNU_SOURCE prior to the inclusion	of <stdio.h> will also make dprintf()
     available.

     The conversion formats %D,	%O, and	%U are not standard and	are provided
     only for backward compatibility.  The effect of padding the %p format
     with zeros	(either	by the 0 flag or by specifying a precision), and the
     benign effect (i.e., none)	of the # flag on %n and	%p conversions,	as
     well as other nonsensical combinations such as %Ld, are not standard;
     such combinations should be avoided.

ERRORS
     In	addition to the	errors documented for the write(2) system call,	the
     printf() family of	functions may fail if:

     [EILSEQ]		An invalid wide	character code was encountered.

     [ENOMEM]		Insufficient storage space is available.

SEE ALSO
     printf(1),	fmtcheck(3), scanf(3), setlocale(3), wprintf(3)

STANDARDS
     Subject to	the caveats noted in the BUGS section below, the fprintf(),
     printf(), sprintf(), vprintf(), vfprintf(), and vsprintf()	functions con-
     form to ANSI X3.159-1989 (``ANSI C89'') and ISO/IEC 9899:1999
     (``ISO C99'').  With the same reservation,	the snprintf() and vsnprintf()
     functions conform to ISO/IEC 9899:1999 (``ISO C99''), while dprintf() and
     vdprintf()	conform	to IEEE	Std 1003.1-2008	(``POSIX.1'').

HISTORY
     The functions asprintf() and vasprintf() first appeared in	the GNU	C
     library.  These were implemented by Peter Wemm <peter@FreeBSD.org>	in
     FreeBSD 2.2, but were later replaced with a different implementation from
     OpenBSD 2.3 by Todd C. Miller <Todd.Miller@courtesan.com>.	 The dprintf()
     and vdprintf() functions were added in FreeBSD 8.0.

BUGS
     The printf	family of functions do not correctly handle multibyte charac-
     ters in the format	argument.

SECURITY CONSIDERATIONS
     The sprintf() and vsprintf() functions are	easily misused in a manner
     which enables malicious users to arbitrarily change a running program's
     functionality through a buffer overflow attack.  Because sprintf()	and
     vsprintf()	assume an infinitely long string, callers must be careful not
     to	overflow the actual space; this	is often hard to assure.  For safety,
     programmers should	use the	snprintf() interface instead.  For example:

     void
     foo(const char *arbitrary_string, const char *and_another)
     {
	     char onstack[8];

     #ifdef BAD
	     /*
	      *	This first sprintf is bad behavior.  Do	not use	sprintf!
	      */
	     sprintf(onstack, "%s, %s",	arbitrary_string, and_another);
     #else
	     /*
	      *	The following two lines	demonstrate better use of
	      *	snprintf().
	      */
	     snprintf(onstack, sizeof(onstack),	"%s, %s", arbitrary_string,
		 and_another);
     #endif
     }

     The printf() and sprintf()	family of functions are	also easily misused in
     a manner allowing malicious users to arbitrarily change a running pro-
     gram's functionality by either causing the	program	to print potentially
     sensitive data ``left on the stack'', or causing it to generate a memory
     fault or bus error	by dereferencing an invalid pointer.

     %n	can be used to write arbitrary data to potentially carefully-selected
     addresses.	 Programmers are therefore strongly advised to never pass
     untrusted strings as the format argument, as an attacker can put format
     specifiers	in the string to mangle	your stack, leading to a possible
     security hole.  This holds	true even if the string	was built using	a
     function like snprintf(), as the resulting	string may still contain user-
     supplied conversion specifiers for	later interpolation by printf().

     Always use	the proper secure idiom:

	   snprintf(buffer, sizeof(buffer), "%s", string);

FreeBSD	10.1		       December	2, 2009			  FreeBSD 10.1

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | EXAMPLES | COMPATIBILITY | ERRORS | SEE ALSO | STANDARDS | HISTORY | BUGS | SECURITY CONSIDERATIONS

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