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NAME

       printf,   fprintf,  sprintf,  snprintf,  vprintf,  vfprintf,  vsprintf,
       vsnprintf - 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, ...);

       #include <stdarg.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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       snprintf(), vsnprintf(): _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
       _ISOC99_SOURCE; or cc -std=c99

DESCRIPTION

       The  functions  in  the  printf()  family produce output according to a
       format as described below.  The functions printf() and vprintf()  write
       output  to stdout, the standard output stream; fprintf() and vfprintf()
       write  output  to  the  given  output  stream;  sprintf(),  snprintf(),
       vsprintf() and vsnprintf() write to the character string str.

       The  functions  snprintf()  and  vsnprintf()  write  at most size bytes
       (including the trailing null byte (’\0’)) to str.

       The  functions  vprintf(),  vfprintf(),  vsprintf(),  vsnprintf()   are
       equivalent to the functions printf(), fprintf(), sprintf(), snprintf(),
       respectively, except that they are called with a va_list instead  of  a
       variable  number  of arguments.  These functions do not call the va_end
       macro.  Because they invoke the  va_arg  macro,  the  value  of  ap  is
       undefined after the call.  See stdarg(3).

       These  eight  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 output.

   Return value
       Upon successful return, these functions return the number of characters
       printed  (not  including  the  trailing  ’\0’  used  to  end  output to
       strings).

       The functions snprintf() and vsnprintf() do not write  more  than  size
       bytes  (including  the trailing ’\0’).  If the output was truncated due
       to this limit then the return value is the number  of  characters  (not
       including the trailing ’\0’) which would have been written to the final
       string if enough space had been available.  Thus,  a  return  value  of
       size  or  more  means  that  the output was truncated.  (See also below
       under NOTES.)

       If an output error is encountered, a negative value is returned.

   Format of the format string
       The format string is a character string, beginning and  ending  in  its
       initial  shift state, if any.  The format string is composed of zero or
       more  directives:  ordinary  characters  (not  %),  which  are   copied
       unchanged  to the output stream; and conversion specifications, each of
       which results in fetching zero  or  more  subsequent  arguments.   Each
       conversion  specification  is  introduced  by the character %, and ends
       with a conversion specifier.  In between there may be (in  this  order)
       zero  or  more  flags,  an  optional  minimum  field width, an optional
       precision and an optional length modifier.

       The arguments must correspond properly (after type promotion) with  the
       conversion  specifier.  By default, the arguments are used in the order
       given, where each ‘*’ and each conversion specifier asks for  the  next
       argument  (and  it  is  an  error  if insufficiently many arguments are
       given).  One can also specify explicitly which argument  is  taken,  at
       each  place  where an argument is required, by writing ‘%m$’ instead of
       ‘%’ and ‘*m$’ instead of ‘*’, where the decimal integer m  denotes  the
       position in the argument list of the desired argument, indexed starting
       from 1.  Thus,

           printf("%*d", width, num);

       and

           printf("%2$*1$d", width, num);

       are equivalent.  The second style allows  repeated  references  to  the
       same  argument.  The C99 standard does not include the style using ‘$’,
       which comes from the Single Unix Specification.  If the style using ‘$’
       is  used,  it  must  be  used  throughout for all conversions taking an
       argument and all width and precision arguments, but  it  may  be  mixed
       with  ‘%%’  formats  which do not consume an argument.  There may be no
       gaps in the numbers of arguments specified using ‘$’; for  example,  if
       arguments  1  and  3  are  specified, argument 2 must also be specified
       somewhere in the format string.

       For some numeric conversions a radix  character  (‘decimal  point’)  or
       thousands’  grouping  character  is  used.   The  actual character used
       depends on the LC_NUMERIC part of the locale.  The  POSIX  locale  uses
       ‘.’ as radix character, and does not have a grouping character.  Thus,

               printf("%’.2f", 1234567.89);

       results  in  ‘1234567.89’  in  the POSIX locale, in ‘1234567,89’ in the
       nl_NL locale, and in ‘1.234.567,89’ in the da_DK locale.

   The flag characters
       The character % is followed by zero or more of the following flags:

       #      The value should be converted to an  "alternate  form".   For  o
              conversions,  the  first  character of the output string is made
              zero (by prefixing a 0 if it was not zero already).  For x and X
              conversions, a nonzero 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 conversions, trailing zeros are not removed from the
              result  as  they would otherwise be.  For other conversions, the
              result is undefined.

       0      The value should be zero padded.  For d, i, o, u, x, X, a, A, e,
              E,  f, F, g, and G conversions, the converted value is padded on
              the left with zeros rather than blanks.  If the 0  and  -  flags
              both  appear,  the  0  flag is ignored.  If a precision is given
              with a numeric conversion (d, i, o, u, x, and X), the 0 flag  is
              ignored.  For other conversions, the behavior is undefined.

       -      The  converted  value  is  to  be  left  adjusted  on  the field
              boundary.  (The default is right justification.)  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.

       ’ ’    (a  space)  A  blank should be left before a positive number (or
              empty string) produced by a signed conversion.

       +      A sign (+ or -) should always be placed before a number produced
              by  a  signed  conversion.   By  default a sign is used only for
              negative numbers.  A + overrides a space if both are used.

       The five flag characters above are defined  in  the  C  standard.   The
       SUSv2 specifies one further flag character.

       ’      For decimal conversion (i, d, u, f, F, g, G) the output is to be
              grouped  with  thousands’  grouping  characters  if  the  locale
              information  indicates  any.   Note that many versions of gcc(1)
              cannot parse this option and will issue a warning.   SUSv2  does
              not include %’F.

       glibc 2.2 adds one further flag character.

       I      For  decimal  integer  conversion  (i, d, u) the output uses the
              locale’s alternative output digits, if any.  For example,  since
              glibc  2.2.3  this  will give Arabic-Indic digits in the Persian
              (‘fa_IR’) locale.

   The field width
       An optional decimal digit string (with nonzero first digit)  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-adjustment  flag  has  been given).  Instead of a
       decimal digit string one may write  ‘*’  or  ‘*m$’  (for  some  decimal
       integer  m)  to  specify  that  the  field  width  is given in the next
       argument, or in the m-th argument, respectively, which must be of  type
       int.   A  negative  field  width  is  taken as a ‘-’ flag followed by a
       positive field width.  In no case does a  nonexistent  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.

   The precision
       An  optional  precision,  in the form of a period (‘.’)  followed by an
       optional decimal digit string.  Instead of a decimal digit  string  one
       may write ‘*’ or ‘*m$’ (for some decimal integer m) to specify that the
       precision is given in the next  argument,  or  in  the  m-th  argument,
       respectively,  which must be of type int.  If the precision is given as
       just ‘.’, or the precision is negative, the precision is  taken  to  be
       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 radix
       character  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 and S conversions.

   The length modifier
       Here, ‘integer conversion’ stands for d, i, o, u, x, or X conversion.

       hh     A  following  integer conversion corresponds to a signed char or
              unsigned char argument, or a following n conversion  corresponds
              to a pointer to a signed char argument.

       h      A  following  integer  conversion  corresponds to a short int or
              unsigned  short  int  argument,  or  a  following  n  conversion
              corresponds to a pointer to a short int argument.

       l      (ell)  A  following integer conversion corresponds to a long int
              or unsigned long int  argument,  or  a  following  n  conversion
              corresponds  to a pointer to a long int argument, or a following
              c conversion corresponds to a wint_t argument, or a following  s
              conversion corresponds to a pointer to wchar_t argument.

       ll     (ell-ell).  A following integer conversion corresponds to a long
              long int or unsigned long long int argument, or  a  following  n
              conversion corresponds to a pointer to a long long int argument.

       L      A following a, A, e, E, f, F, g, or G conversion corresponds  to
              a long double argument.  (C99 allows %LF, but SUSv2 does not.)

       q      (‘quad’.  4.4BSD  and  Linux libc5 only.  Don’t use.)  This is a
              synonym for ll.

       j      A following integer conversion corresponds  to  an  intmax_t  or
              uintmax_t argument.

       z      A  following  integer  conversion  corresponds  to  a  size_t or
              ssize_t argument.  (Linux libc5 has Z with this meaning.   Don’t
              use it.)

       t      A  following  integer  conversion  corresponds  to  a  ptrdiff_t
              argument.

       The SUSv2 only knows about the length modifiers h (in hd, hi,  ho,  hx,
       hX, hn) and l (in ld, li, lo, lx, lX, ln, lc, ls) and L (in Le, LE, Lf,
       Lg, LG).

   The conversion specifier
       A character that specifies the type of conversion to be  applied.   The
       conversion specifiers and their meanings are:

       d,i    The  int  argument is converted to signed decimal notation.  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.   The  default  precision  is  1.
              When  0  is  printed with an explicit precision 0, the output is
              empty.

       o,u,x,X
              The unsigned int argument is converted to  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.  The default precision is 1.  When 0 is printed with
              an explicit precision 0, the output is empty.

       e,E    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
              precision; if the precision is missing, it is taken as 6; if the
              precision  is  zero,  no  decimal-point character appears.  An E
              conversion 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.

       f,F    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.

              (The  SUSv2 does not know about F and says that character string
              representations for infinity and NaN may be made available.  The
              C99  standard  specifies ‘[-]inf’ or ‘[-]infinity’ for infinity,
              and a string starting with ‘nan’ for  NaN,  in  the  case  of  f
              conversion,  and ‘[-]INF’ or ‘[-]INFINITY’ or ‘NAN*’ in the case
              of F conversion.)

       g,G    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.

       a,A    (C99;  not  in  SUSv2)  For a conversion, the double argument is
              converted to hexadecimal notation (using the letters abcdef)  in
              the  style  [-]0xh.hhhhp±d;  for A conversion the prefix 0X, the
              letters ABCDEF, and the exponent separator P is used.  There  is
              one  hexadecimal  digit before the decimal point, and the number
              of digits after it is  equal  to  the  precision.   The  default
              precision  suffices  for an exact representation of the value if
              an exact representation  in  base  2  exists  and  otherwise  is
              sufficiently  large  to  distinguish values of type double.  The
              digit before the decimal point is unspecified for non-normalized
              numbers,  and  nonzero  but otherwise unspecified for normalized
              numbers.

       c      If no l modifier is present, the int argument is converted to an
              unsigned  char, and the resulting character is written.  If an l
              modifier is present, the wint_t  (wide  character)  argument  is
              converted  to  a  multibyte sequence by a call to the wcrtomb(3)
              function, with a conversion state starting in the initial state,
              and the resulting multibyte string is written.

       s      If  no  l  modifier  is  present:  The  const 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 null byte (’\0’); if a precision is
              specified,  no more than the number specified are written.  If a
              precision is given,  no  null  byte  need  be  present;  if  the
              precision  is  not specified, or is greater than the size of the
              array, the array must contain a terminating null byte.

              If an l modifier is present: The const  wchar_t  *  argument  is
              expected  to  be a pointer to an array of wide characters.  Wide
              characters from the array are converted to multibyte  characters
              (each  by  a  call to the wcrtomb(3) function, with a conversion
              state starting in  the  initial  state  before  the  first  wide
              character),   up  to  and  including  a  terminating  null  wide
              character.  The resulting multibyte characters are written up to
              (but  not  including) the terminating null byte.  If a precision
              is specified, no  more  bytes  than  the  number  specified  are
              written,  but no partial multibyte characters are written.  Note
              that the precision determines the number of bytes  written,  not
              the  number  of  wide characters or screen positions.  The array
              must  contain  a  terminating  null  wide  character,  unless  a
              precision  is  given and it is so small that the number of bytes
              written exceeds it before the end of the array is reached.

       C      (Not in C99, but in SUSv2.)  Synonym for lc.  Don’t use.

       S      (Not in C99, but in SUSv2.)  Synonym for ls.  Don’t use.

       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
              integer indicated by the int * (or  variant)  pointer  argument.
              No argument is converted.

       m      (Glibc   extension.)    Print  output  of  strerror(errno).   No
              argument is required.

       %      A ‘%’ is written.   No  argument  is  converted.   The  complete
              conversion specification is ‘%%’.

CONFORMING TO

       The   fprintf(),   printf(),   sprintf(),  vprintf(),  vfprintf(),  and
       vsprintf() functions conform  to  C89  and  C99.   The  snprintf()  and
       vsnprintf() functions conform to C99.

       Concerning  the  return  value  of snprintf(), SUSv2 and C99 contradict
       each other: when snprintf() is called with size=0 then SUSv2 stipulates
       an  unspecified  return  value  less than 1, while C99 allows str to be
       NULL in this case, and gives the return value (as always) as the number
       of  characters  that  would have been written in case the output string
       has been large enough.

       Linux libc4 knows about the five C standard flags.  It knows about  the
       length  modifiers  h,l,L, and the conversions cdeEfFgGinopsuxX, where F
       is a synonym for f.  Additionally, it accepts  D,O,U  as  synonyms  for
       ld,lo,lu.   (This  is  bad, and caused serious bugs later, when support
       for  %D  disappeared.)   No  locale-dependent   radix   character,   no
       thousands’ separator, no NaN or infinity, no %m$ and *m$.

       Linux  libc5  knows  about  the  five  C standard flags and the ’ flag,
       locale, %m$ and *m$.  It knows about the  length  modifiers  h,l,L,Z,q,
       but accepts L and q both for long double and for long long int (this is
       a bug).   It  no  longer  recognizes  FDOU,  but  adds  the  conversion
       character m, which outputs strerror(errno).

       glibc 2.0 adds conversion characters C and S.

       glibc 2.1 adds length modifiers hh,j,t,z and conversion characters a,A.

       glibc 2.2 adds the conversion character F with C99 semantics,  and  the
       flag character I.

NOTES

       The  glibc  implementation  of the functions snprintf() and vsnprintf()
       conforms to the C99 standard, that  is,  behaves  as  described  above,
       since  glibc  version 2.1.  Until glibc 2.0.6 they would return -1 when
       the output was truncated.

BUGS

       Because sprintf() and vsprintf() assume  an  arbitrarily  long  string,
       callers must be careful not to overflow the actual space; this is often
       impossible to assure.  Note that the length of the strings produced  is
       locale-dependent   and   difficult  to  predict.   Use  snprintf()  and
       vsnprintf() instead (or asprintf(3) and vasprintf(3)).

       Linux libc4.[45] does not have a snprintf(), but provides a libbsd that
       contains  an  snprintf()  equivalent  to  sprintf(),  that is, one that
       ignores the size argument.  Thus, the  use  of  snprintf()  with  early
       libc4 leads to serious security problems.

       Code  such as printf(foo); often indicates a bug, since foo may contain
       a % character.  If foo comes from untrusted user input, it may  contain
       %n,  causing  the  printf()  call  to  write  to  memory and creating a
       security hole.

EXAMPLE

       To print pi to five decimal places:

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

       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);

       Many    countries    use   the   day-month-year   order.    Hence,   an
       internationalized version must be able to print  the  arguments  in  an
       order specified by the format:

           #include <stdio.h>
           fprintf(stdout, format,
                   weekday, month, day, hour, min);

       where  format  depends  on locale, and may permute the arguments.  With
       the value:

           "%1$s, %3$d. %2$s, %4$d:%5$.2d\n"

       one might obtain ‘Sonntag, 3. Juli, 10:02’.

       To allocate a sufficiently large string and print into it (code correct
       for both glibc 2.0 and glibc 2.1):

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

       char *
       make_message(const char *fmt, ...)
       {
           /* Guess we need no more than 100 bytes. */
           int n, size = 100;
           char *p, *np;
           va_list ap;

           if ((p = malloc(size)) == NULL)
               return NULL;

           while (1) {
               /* Try to print in the allocated space. */
               va_start(ap, fmt);
               n = vsnprintf(p, size, fmt, ap);
               va_end(ap);
               /* If that worked, return the string. */
               if (n > -1 && n < size)
                   return p;
               /* Else try again with more space. */
               if (n > -1)    /* glibc 2.1 */
                   size = n+1; /* precisely what is needed */
               else           /* glibc 2.0 */
                   size *= 2;  /* twice the old size */
               if ((np = realloc (p, size)) == NULL) {
                   free(p);
                   return NULL;
               } else {
                   p = np;
               }
           }
       }

SEE ALSO

       printf(1), asprintf(3), dprintf(3), scanf(3), setlocale(3), wcrtomb(3),
       wprintf(3), locale(5)

COLOPHON

       This page is part of release 2.77 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.