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FPRINTF(2)                    System Calls Manual                   FPRINTF(2)



NAME
       fprintf,   printf,  sprintf,  snprintf,  vfprintf,  vprintf,  vsprintf,
       vsnprintf - print formatted output

SYNOPSIS
       #include <u.h>
       #include <stdio.h>

       int fprintf(FILE *f, char *format, ...)

       int printf(char *format, ...)

       int sprintf(char *s, char *format, ...)

       int snprintf(char *s, int n, char *format, ...)

       int vfprintf(FILE *f, char *format, va_list args)

       int vprintf(char *format, va_list args)

       int vsprintf(char *s, char *format, va_list args)

       int vsnprintf(char *s, int n, char *format, va_list args)

DESCRIPTION
       Fprintf places output on the named  output  stream  f  (see  fopen(2)).
       Printf  places  output  on  the standard output stream stdout.  Sprintf
       places output followed by the null character (\0) in consecutive  bytes
       starting  at  s;  it is the user's responsibility to ensure that enough
       storage is available.  Snprintf is like sprintf but writes  at  most  n
       bytes  (including  the  null  character)  into  s.   Vfprintf, vprintf,
       vsnprintf, and vsprintf are the same, except the args argument  is  the
       argument  list  of  the  calling  function, and the effect is as if the
       calling function's argument list from that point on is  passed  to  the
       printf routines.

       Each function returns the number of characters transmitted (not includ‐
       ing the \0 in the case of sprintf and friends), or a negative value  if
       an output error was encountered.

       These  functions  convert,  format,  and print their trailing arguments
       under control of a format string.  The format  contains  two  types  of
       objects:  plain  characters,  which  are  simply  copied  to the output
       stream, and conversion specifications, each of which results in  fetch‐
       ing  of zero or more arguments.  The results are undefined if there are
       arguments of the wrong type or too few arguments for  the  format.   If
       the format is exhausted while arguments remain, the excess are ignored.

       Each  conversion specification is introduced by the character %.  After
       the %, the following appear in sequence:

              Zero or more flags, which modify the meaning of  the  conversion
              specification.

              An  optional  decimal  digit  string  specifying a minimum field
              width.  If the converted value has  fewer  characters  than  the
              field  width,  it  will  be  padded  with spaces on the left (or
              right, if the left adjustment, described later, has been  given)
              to the field width.

              An optional precision that gives the minimum number of digits to
              appear for the d, i, o, u, x, and X conversions, the  number  of
              digits  to  appear  after  the decimal point for the e, E, and f
              conversions, the maximum number of significant digits for the  g
              and  G  conversions,  or  the maximum number of characters to be
              written from a string in s conversion.  The precision takes  the
              form  of  a period (.)  followed by an optional decimal integer;
              if the integer is omitted, it is treated as zero.

              An optional h specifying that a following d, i, o,  u,  x  or  X
              conversion  specifier  applies  to a short int or unsigned short
              argument (the argument will have been promoted according to  the
              integral  promotions,  and its value shall be converted to short
              or unsigned short before printing);  an  optional  h  specifying
              that  a following n conversion specifier applies to a pointer to
              a short argument; an optional l (ell) specifying that a  follow‐
              ing  d,  i, o, u, x, or X conversion character applies to a long
              or unsigned long argument; an optional l specifying that a  fol‐
              lowing n conversion specifier applies to a pointer to a long int
              argument; or an optional L specifying that a following e, E,  f,
              g,  or G conversion specifier applies to a long double argument.
              If an h, l, or L appears with any  other  conversion  specifier,
              the behavior is undefined.

              A character that indicates the type of conversion to be applied.

       A  field  width  or precision, or both, may be indicated by an asterisk
       (*) instead of a digit string.  In this case, an int arg  supplies  the
       field width or precision.  The arguments specifying field width or pre‐
       cision, or both, shall appear (in that order) before the  argument  (if
       any)  to be converted.  A negative field width argument is taken as a -
       flag followed by a positive field width.  A negative precision is taken
       as if it were missing.

       The flag characters and their meanings are:
       -         The  result  of  the  conversion is left-justified within the
                 field.
       +         The result of a signed conversion always begins with  a  sign
                 (+ or -).
       blank     If  the first character of a signed conversion is not a sign,
                 or a signed conversion results in no characters, a  blank  is
                 prefixed to the result.  This implies that if the blank and +
                 flags both appear, the blank flag is ignored.
       #         The result is to be converted to an ``alternate form.''   For
                 o  conversion,  it increases the precision to force the first
                 digit of the result to be a zero.  For x or X  conversion,  a
                 non-zero result has 0x or 0X prefixed to it.  For e, E, f, g,
                 and G conversions,  the  result  always  contains  a  decimal
                 point,  even if no digits follow the point (normally, a deci‐
                 mal point appears in the result of these conversions only  if
                 a digit follows it).  For g and G conversions, trailing zeros
                 are not be removed from the result as they normally are.  For
                 other conversions, the behavior is undefined.
       0         For  d, i, o, u, x, X, e, E, f, g, and G conversions, leading
                 zeros (following any indication of sign or base) are used  to
                 pad the field width; no space padding is performed.  If the 0
                 and - flags both appear, the 0 flag will be ignored.  For  d,
                 i,  o,  u, x, and X conversions, if a precision is specified,
                 the 0 flag will  be  ignored.   For  other  conversions,  the
                 behavior is undefined.

       The conversion characters and their meanings are:

       d,o,u,x,X The  integer  arg  is  converted  to signed decimal (d or i),
                 unsigned octal (o), unsigned decimal (u), or  unsigned  hexa‐
                 decimal  notation (x or X); the letters abcdef are used for x
                 conversion and the letters ABCDEF for X conversion.  The pre‐
                 cision  specifies  the minimum number of digits to appear; if
                 the value being converted can be represented in fewer digits,
                 it  is expanded with leading zeros.  The default precision is
                 1.  The result of converting a zero value with a precision of
                 zero is no characters.
       f         The  double  argument is converted to decimal notation in the
                 style [-]ddd.ddd, where the number of digits after the  deci‐
                 mal  point  is  equal to the precision specification.  If the
                 precision is missing, it is taken as 6; if the  precision  is
                 explicitly no decimal point appears.
       e,E       The  double argument is converted in the style [-]d.ddde±dd,
                 where there is one digit before the  decimal  point  and  the
                 number of digits after it is equal to the precision; when the
                 precision is missing, it is taken as 6; if the  precision  is
                 zero, no decimal point appears.  The E format code produces a
                 number with E instead of e  introducing  the  exponent.   The
                 exponent always contains at least two digits.
       g,G       The double argument is printed in style f or e (or in style E
                 in the case of a G conversion specifier), with the  precision
                 specifying  the number of significant digits.  If an explicit
                 precision is zero, it is taken as 1.  The style used  depends
                 on  the value converted: style e is used only if the exponent
                 resulting from the conversion is less than -4 or greater than
                 or  equal  to the precision.  Trailing zeros are removed from
                 the fractional portion of the result; a decimal point appears
                 only if it is followed by a digit.
       c         The  int  argument  is converted to an unsigned char, and the
                 resulting character is written.
       s         The argument is taken to be a string (character pointer)  and
                 characters from the string are printed until a null character
                 (\0) is encountered or the number of characters indicated  by
                 the  precision specification is reached.  If the precision is
                 missing, it is taken to be infinite, so all characters up  to
                 the  first  null character are printed.  A zero value for the
                 argument yields undefined results.
       P         The void* argument is printed  in  an  implementation-defined
                 way (for Plan 9: the address as hexadecimal number).
       n         The  argument  shall be a pointer to an integer into which is
                 written the number of characters written to the output stream
                 so far by this call to fprintf.  No argument is converted.
       %         Print a %; no argument is converted.

       If a conversion specification is invalid, the behavior is undefined.

       If  any  argument is, or points to, a union or an aggregate (except for
       an array of character type using %s conversion, or a pointer cast to be
       a pointer to void using %P conversion), the behavior is undefined.

       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.

SOURCE
       /sys/src/libstdio

SEE ALSO
       fopen(2), fscanf(2), print(2)

BUGS
       There  is  no  way  to  print  a wide character (rune); use print(2) or
       bio(2).



                                                                    FPRINTF(2)