Provided by: manpages-dev_4.04-2_all bug

NAME

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

SYNOPSIS

       #include <stdio.h>

       int printf(const char *format, ...);
       int fprintf(FILE *stream, const char *format, ...);
       int dprintf(int fd, 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 vdprintf(int fd, 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

       dprintf(), vdprintf():
           Since glibc 2.10:
               _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
               _GNU_SOURCE

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 function dprintf() is the same as fprintf(3) except that it outputs
       to a file descriptor, fd, instead of to a stdio stream.

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

       The    functions   vprintf(),   vfprintf(),   vdprintf(),   vsprintf(),
       vsnprintf()  are  equivalent  to  the  functions  printf(),  fprintf(),
       dprintf(),  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).

       All of 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 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.

   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  '*' (see Field width and Precision below) 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.

   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.)  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  C99  standard.   The
       Single UNIX Specification 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  did
              not include %'F, but SUSv3 added it.)

       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.

   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.

   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 '.', the precision is taken to be zero.  A negative  precision  is
       taken  as if the precision were omitted.  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.

   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.)
              This is a synonym for ll.

       j      A following integer conversion corresponds  to  an  intmax_t  or
              uintmax_t argument, or a following n conversion corresponds to a
              pointer to an intmax_t argument.

       z      A following  integer  conversion  corresponds  to  a  size_t  or
              ssize_t  argument,  or a following n conversion corresponds to a
              pointer to a size_t argument.

       t      A  following  integer  conversion  corresponds  to  a  ptrdiff_t
              argument,  or  a following n conversion corresponds to a pointer
              to a ptrdiff_t argument.

       SUSv3 specifies all of the above.   SUSv2  specified  only  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).

   Conversion specifiers
       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.

              (SUSv2  does  not  know  about  F and says that character string
              representations for infinity and  NaN  may  be  made  available.
              SUSv3  adds  a  specification for F.  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, but added in SUSv3) For a conversion, the
              double argument is converted to hexadecimal notation (using  the
              letters abcdef) in the style [-]0xh.hhhhp±; 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 or C11, but in SUSv2, SUSv3,  and  SUSv4.)   Synonym
              for lc.  Don't use.

       S      (Not  in  C99  or C11, but in SUSv2, SUSv3, and SUSv4.)  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 pointed to by the corresponding argument.  That argument
              shall   be   an   int *,  or  variant  whose  size  matches  the
              (optionally) supplied integer length modifier.  No  argument  is
              converted.    The   behavior  is  undefined  if  the  conversion
              specification includes any flags, a field width, or a precision.

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

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

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.

ATTRIBUTES

       For   an   explanation   of   the  terms  used  in  this  section,  see
       attributes(7).

       ┌────────────────────────┬───────────────┬────────────────┐
       │InterfaceAttributeValue          │
       ├────────────────────────┼───────────────┼────────────────┤
       │printf(), fprintf(),    │ Thread safety │ MT-Safe locale │
       │sprintf(), snprintf(),  │               │                │
       │vprintf(), vfprintf(),  │               │                │
       │vsprintf(), vsnprintf() │               │                │
       └────────────────────────┴───────────────┴────────────────┘

CONFORMING TO

       fprintf(),  printf(),  sprintf(),  vprintf(),  vfprintf(),  vsprintf():
       POSIX.1-2001, POSIX.1-2008, C89, C99.

       snprintf(), vsnprintf(): POSIX.1-2001, POSIX.1-2008, C99.

       The  dprintf()  and vdprintf() functions were originally GNU extensions
       that were later standardized in POSIX.1-2008.

       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.    POSIX.1-2001   and  later  align  their
       specification of snprintf() with C99.

       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)).

       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 size = 0;
           char *p = NULL;
           va_list ap;

           /* Determine required size */

           va_start(ap, fmt);
           size = vsnprintf(p, size, fmt, ap);
           va_end(ap);

           if (size < 0)
               return NULL;

           size++;             /* For '\0' */
           p = malloc(size);
           if (p == NULL)
               return NULL;

           va_start(ap, fmt);
           size = vsnprintf(p, size, fmt, ap);
           if (size < 0) {
               free(p);
               return NULL;
           }
           va_end(ap);

           return p;
       }

       If  truncation occurs in glibc versions prior to 2.0.6, this is treated
       as an error instead of being handled gracefully.

SEE ALSO

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

COLOPHON

       This  page  is  part of release 4.04 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.