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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():
           _XOPEN_SOURCE >= 500 || _ISOC99_SOURCE ||
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE

       dprintf(), vdprintf():
           Since glibc 2.10:
               _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()  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.  (See setlocale(3).)  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.   (See
              setlocale(3).)  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.

       q      A synonym for ll.  This is a nonstandard extension, derived from BSD; avoid its use
              in new code.

       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.)

       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.

       Z      A  nonstandard  synonym for z that predates the appearance of z.  Do not use in new
              code.

       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, except for those modifiers explicitly noted as being
       nonstandard extensions.  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).

       As  a  nonstandard extension, the GNU implementations treats ll and L as synonyms, so that
       one can, for example, write llg (as a synonym for the standards-compliant Lg) and Ld (as a
       synonym for the standards compliant lld).  Such usage is nonportable.

   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.   (This  specifier  is  not  supported  by  the  bionic C library.)  The
              behavior is undefined if the conversion specification includes any flags,  a  field
              width, or a precision.

       m      (Glibc  extension; supported by uClibc and musl.)  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);
           va_end(ap);

           if (size < 0) {
               free(p);
               return NULL;
           }

           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),   puts(3),   scanf(3),  setlocale(3),  strfromd(3),  wcrtomb(3),
       wprintf(3), locale(5)

COLOPHON

       This page is part of release 4.16 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 https://www.kernel.org/doc/man-pages/.