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PRINTF(3)		 BSD Library Functions Manual		     PRINTF(3)

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

SYNOPSIS
     #include <stdio.h>

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

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

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

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

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

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

     #include <stdarg.h>
     #include <stdio.h>

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

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

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

     int
     vsnprintf(char *str, size_t size, const char *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 produce output according to the given
     format as described below.	 This format may contain "conversion
     specifiers"; the results of such conversions, if any, depend on the argu-
     ments following the format	string.

     The printf() and vprintf()	functions write	output to the standard output
     stream, stdout; fprintf() and vfprintf() write output to the supplied
     stream pointer stream; dprintf() and vdprintf() write output to the given
     file descriptor; sprintf(), snprintf(), vsprintf(), and vsnprintf() write
     to	the character string str; asprintf() and vasprintf() write to a	dynam-
     ically allocated string that is stored in ret.

     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.

     snprintf()	and vsnprintf()	will write at most size-1 of the characters
     printed into the output string (the size'th character then	gets the ter-
     minating `\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.  If size is zero, str may be a null pointer and no	char-
     acters will be written; the number	of bytes that would have been written
     excluding the terminating `\0' byte, or -1	on error, will be returned.

     sprintf() and vsprintf() 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.

     +o	 Zero or more of the following flags:

	 -   A hash `#'	character specifying that the value should be con-
	     verted to an "alternate form".  For o conversions,	the precision
	     of	the number is increased	to force the first character of	the
	     output string to a	zero (except if	a zero value is	printed	with
	     an	explicit precision of zero).  For x and	X conversions, a non-
	     zero result has the string	`0x' (or `0X' for X conversions)
	     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 conver-
	     sions, trailing zeros are not removed from	the result as they
	     would otherwise be.  For all other	formats, behaviour is unde-
	     fined.

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

	 -   A negative	field width flag `-' indicates the converted value is
	     to	be left	adjusted on the	field boundary.	 Except	for n conver-
	     sions, 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.

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

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

     +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 op-
	 tional	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 conversions:

	 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 an 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 modifiers	are valid for the a, A,	e, E, f, F, g,
	 or G conversions:

	 Modifier    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 conversions:

	 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 conver-
	     sions.  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	expo-
	     nent.  The	exponent always	contains at least two digits; if the
	     value is zero, the	exponent is 00.

	     If	the argument is	infinity, it will be converted to [-]inf (e)
	     or	[-]INF (E), respectively.  If the argument is not-a-number
	     (NaN), it will be converted to [-]nan (e) or [-]NAN (E), respec-
	     tively.

     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.

	     If	the argument is	infinity, it will be converted to [-]inf (f)
	     or	[-]INF (F), respectively.  If the argument is not-a-number
	     (NaN), it will be converted to [-]nan (f) or [-]NAN (F), respec-
	     tively.

     gG	     The double	argument is converted in style f or e (or E for	G con-
	     versions).	 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.

	     If	the argument is	infinity, it will be converted to [-]inf (g)
	     or	[-]INF (G), respectively.  If the argument is not-a-number
	     (NaN), it will be converted to [-]nan (g) or [-]NAN (G), respec-
	     tively.

     aA	     The double	argument is rounded and	converted to hexadecimal nota-
	     tion in the style [-]0xh.hhhp[+-]d	where the number of digits af-
	     ter 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 ex-
	     ponent consists of	a positive or negative sign followed by	a dec-
	     imal 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,
	     0x3.24p+0,	0x6.48p-1 and 0xc.9p-2 are all equivalent.  The	format
	     chosen depends on the internal representation of the number, but
	     the implementation	guarantees that	the length of the mantissa
	     will be minimized.	 Zeroes	are always represented with a mantissa
	     of	0 (preceded by a `-' if	appropriate) and an exponent of	+0.

	     If	the argument is	infinity, it will be converted to [-]inf (a)
	     or	[-]INF (A), respectively.  If the argument is not-a-number
	     (NaN), it will be converted to [-]nan (a) or [-]NAN (A), respec-
	     tively.

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

     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 NUL	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.

     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 ar-
	     gument is converted.

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

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

RETURN VALUES
     For all these functions if	an output or encoding error occurs, a value
     less than 0 is returned.

     The printf(), dprintf(), fprintf(), sprintf(), vprintf(), vdprintf(),
     vfprintf(), vsprintf(), asprintf(), and vasprintf() functions return the
     number of characters printed (not including the trailing `\0' used	to end
     output to strings).

     The snprintf() and	vsnprintf() functions return the number	of characters
     that would	have been output if the	size were unlimited (again, not
     including the final `\0'.).

     The asprintf() and	vasprintf() functions return the number	of characters
     that were output to the newly allocated string (excluding the final
     `\0').  A pointer to the newly allocated string is	returned in ret; it
     should be passed to free(3) to release the	allocated storage when it is
     no	longer needed.	If sufficient space cannot be allocated, these func-
     tions will	return -1.  The	value of ret in	this situation is implementa-
     tion-dependent (on	OpenBSD, ret will be set to the	null pointer, but this
     behavior should not be relied upon).

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 <stdarg.h>
	   #include <stdio.h>
	   #include <stdlib.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);
	   }

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.

     [EOVERFLOW]	The return value would be too large to be represented
			by an int.

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

STANDARDS
     The fprintf(), printf(), snprintf(), sprintf(), vfprintf(), vprintf(),
     vsnprintf(), and vsprintf() functions conform to ISO/IEC 9899:1999
     ("ISO C99").  The dprintf() and vdprintf()	functions conform to IEEE Std
     1003.1-2008 ("POSIX.1").

HISTORY
     The predecessors ftoa() and itoa()	first appeared in Version 1 AT&T UNIX.
     The function printf() first appeared in Version 2 AT&T UNIX, and
     fprintf() and sprintf() in	Version	7 AT&T UNIX.

     The functions snprintf() and vsnprintf() first appeared in	4.4BSD.

     The functions asprintf() and vasprintf() first appeared in	the GNU	C li-
     brary.  This implementation first appeared	in OpenBSD 2.3.

     The functions dprintf() and vdprintf() first appeared in OpenBSD 5.3.

CAVEATS
     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.

     Because sprintf() and vsprintf() assume an	infinitely long	string,	call-
     ers must be careful not to	overflow the actual space; this	is often im-
     possible to assure.  For safety, programmers should use the snprintf()
     and asprintf() family of interfaces instead.  Unfortunately, the
     asprintf()	interface is not available on all systems as it	is not part of
     ISO/IEC 9899:1999 ("ISO C99").

     It	is important never to pass a string with user-supplied data as a for-
     mat without using `%s'.  An attacker can put format specifiers in the
     string to mangle the stack, leading to a possible security	hole.  This
     holds true	even if	the string has been built "by hand" using a function
     like snprintf(), as the resulting string may still	contain	user-supplied
     conversion	specifiers for later interpolation by printf().

     Be	sure to	use the	proper secure idiom:

	   int ret = snprintf(buffer, sizeof(buffer), "%s", string);
	   if (ret == -1 || ret	>= sizeof(buffer))
		   goto	toolong;

     There is no way for printf() to know the size of each argument passed.
     If	positional arguments are used, care must be taken to ensure that all
     parameters, up to the last	positionally specified parameter, are used in
     the format	string.	 This allows for the format string to be parsed	for
     this information.	Failure	to do this will	mean the code is non-portable
     and liable	to fail.

     On	systems	other than OpenBSD, the	LC_NUMERIC locale(1) category can
     cause erratic output; see CAVEATS in setlocale(3) for details.

BSD			       January 16, 2019				   BSD

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | ERRORS | SEE ALSO | STANDARDS | HISTORY | CAVEATS

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