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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 ||
           _POSIX_C_SOURCE >= 200112L;
           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 terminating 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.

       C99 and POSIX.1-2001 specify that the results are undefined if  a  call
       to  sprintf(),  snprintf(),  vsprintf(),  or  vsnprintf()  would  cause
       copying to take place between objects that overlap (e.g., if the target
       string  array and one of the supplied input arguments refer to the same
       buffer).  See NOTES.

   Return value
       Upon successful return, these functions return the number of characters
       printed (excluding the null byte used to end output to strings).

       The  functions  snprintf()  and vsnprintf() do not write more than size
       bytes (including the terminating null byte ('\0')).  If the output  was
       truncated  due  to  this  limit  then the return value is the number of
       characters (excluding the terminating null byte) 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  nonnormalized
              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 c, d, e, E, f, F, g, G,
       i, n, o, p, s, u, x, and X, where F is a synonym for f.   Additionally,
       it  accepts  D, O, and U as synonyms for ld, lo, and 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, and q, but accepts L and q both for long double and  for  long  long
       int  (this is a bug).  It no longer recognizes F, D, O, and U, 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,  and  z  and  conversion
       characters a and A.

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

NOTES

       Some programs imprudently rely on code such as the following

           sprintf(buf, "%s some further text", buf);

       to append text to buf.  However, the standards explicitly note that the
       results  are  undefined  if source and destination buffers overlap when
       calling sprintf(), snprintf(), vsprintf(), and vsnprintf().   Depending
       on the version of gcc(1) used, and the compiler options employed, calls
       such as the above will not produce the expected results.

       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, ...)
       {
           int n;
           int size = 100;     /* Guess we need no more than 100 bytes. */
           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 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.