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printf

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printf

 

NAME

printf,  fprintf,  sprintf,  vprintf, vfprintf, vsprintf -
       formatted output conversion

SYNOPSIS

<strong>#include</strong> <strong>&lt;stdio.h&gt;</strong>
<strong>int</strong> <strong>printf(</strong> <strong>const</strong> <strong>char</strong> <strong>*</strong><em>format</em><strong>,</strong> <strong>...);</strong>
<strong>int</strong> <strong>fprintf(</strong> <strong>FILE</strong> <strong>*</strong><em>stream</em><strong>,</strong> <strong>const</strong> <strong>char</strong> <strong>*</strong><em>format</em><strong>,</strong> <strong>...);</strong>
<strong>int</strong> <strong>sprintf(</strong> <strong>char</strong> <strong>*</strong><em>str</em><strong>,</strong> <strong>const</strong> <strong>char</strong> <strong>*</strong><em>format</em><strong>,</strong> <strong>...);</strong>
<strong>#include</strong> <strong>&lt;stdarg.h&gt;</strong>
<strong>int</strong> <strong>vprintf(</strong> <strong>const</strong> <strong>char</strong> <strong>*</strong><em>format</em><strong>,</strong> <strong>va_list</strong> <em>ap</em><strong>);</strong>
<strong>int</strong> <strong>vfprintf(</strong> <strong>FILE</strong> <strong>*</strong><em>stream</em><strong>,</strong> <strong>const</strong> <strong>char</strong> <strong>*</strong><em>format</em><strong>,</strong> <strong>va_list</strong>
<em>ap</em><strong>);</strong>
<strong>int</strong> <strong>vsprintf(</strong> <strong>char</strong> <strong>*</strong><em>str</em><strong>,</strong> <strong>char</strong> <strong>*</strong><em>format</em><strong>,</strong> <strong>va_list</strong> <em>ap</em><strong>);</strong>

DESCRIPTION

The  <strong>printf</strong>  family of functions produces output according
       to a <em>format</em> as described below.  <strong>Printf</strong> and <strong>vprintf</strong>  write
       output  to <em>stdout</em>, the standard output stream; <strong>fprintf</strong> and
       <strong>vfprintf</strong> write output to the given output <em>stream</em>; <strong>sprintf</strong>,
       and  <strong>vsprintf</strong>  write  to  the character string <em>str</em>.  These
       functions write the output under the control of  a  <em>format</em>
       string  that  specifies how subsequent arguments (or argu-
       ments accessed via the variable-length argument facilities
       of  <strong><a href="http://man.he.net/man3/stdarg">stdarg(3)</a></strong>  are  converted for output.  These functions
       return the number of characters printed (not including the
       trailing `' used to end output to strings).

       The  format string is composed of zero or more directives:
       ordinary characters (not <strong>%</strong>), which are copied unchanged to
       the  output stream; and conversion specifications, each of
       which results in fetching zero or  more  subsequent  argu-
       ments.  Each conversion specification is introduced by the
       character  <strong>%</strong>.   The  arguments  must  correspond  properly
       (after  type  promotion)  with  the  conversion specifier.
       After the <strong>%</strong>, the following appear in sequence:

       <strong>o</strong>      Zero or more of the following flags:

              <strong>#</strong>      specifying that the  value  should  be  con-
                     verted  to an ``alternate form''.  For <strong>c</strong>, <strong>d</strong>,
                     <strong>i</strong>, <strong>n</strong>, <strong>p</strong>, <strong>s</strong>, and <strong>u</strong> conversions,  this  option
                     has  no effect.  For <strong>o</strong> conversions, the pre-
                     cision of the number is increased  to  force
                     the  first character of the output string to
                     a zero (except if a zero  value  is  printed
                     with  an explicit precision of zero).  For <strong>x</strong>
                     and <strong>X</strong> conversions, a non-zero result has the
                     string  `0x'  (or  `0X'  for  <strong>X</strong> conversions)
                     prepended to it.  For <strong>e</strong>, <strong>E</strong>, <strong>f</strong>, <strong>g</strong>, and <strong>G</strong> con-
                     versions,  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 <strong>g</strong> and <strong>G</strong> conversions, trailing
                     zeros are not removed  from  the  result  as
                     they would otherwise be.

              <strong>0</strong>      specifying  zero  padding.   For all conver-
                     sions  except  <strong>n</strong>,  the  converted  value  is
                     padded  on  the  left with zeros rather than
                     blanks.  If a  precision  is  given  with  a
                     numeric  conversion  (<strong>d</strong>,  <strong>i</strong>, <strong>o</strong>, <strong>u</strong>, <strong>i</strong>, <strong>x</strong>, and
                     <strong>X</strong>), the <strong>0</strong> flag is ignored.

              <strong>-</strong>      (a negative field width flag) indicates  the
                     converted  value  is  to be left adjusted on
                     the field boundary.  Except  for  <strong>n</strong>  conver-
                     sions,  the converted value is padded on the
                     right with blanks, rather than on  the  left
                     with  blanks or zeros.  A <strong>-</strong> overrides a <strong>0</strong> if
                     both are given.

                     (a space) specifying that a blank should  be
                     left  before a positive number produced by a
                     signed conversion (<strong>d</strong>, <strong>e</strong>, <strong>E</strong>, <strong>f</strong>, <strong>g</strong>, <strong>G</strong>, or  <strong>i</strong>).

              <strong>+</strong>      specifying  that  a  sign  always  be placed
                     before a number produced by a signed conver-
                     sion.   A  <strong>+</strong>  overrides  a space if both are
                     used.

       <strong>o</strong>      An optional decimal digit string specifying a mini-
              mum  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)  to  fill  out  the
              field width.

       <strong>o</strong>      An  optional  precision,  in  the  form of a period
              (`.')  followed by an optional  digit  string.   If
              the digit string is omitted, the precision is taken
              as zero.  This gives the minimum number  of  digits
              to appear for <strong>d</strong>, <strong>i</strong>, <strong>o</strong>, <strong>u</strong>, <strong>x</strong>, and <strong>X</strong> conversions, the
              number of digits to appear after the  decimal-point
              for  <strong>e</strong>, <strong>E</strong>, and <strong>f</strong> conversions, the maximum number of
              significant digits for <strong>g</strong> and <strong>G</strong> conversions, or  the
              maximum  number  of characters to be printed from a
              string for <strong>s</strong> conversions.

       <strong>o</strong>      The optional character <strong>h</strong>, specifying that a follow-
              ing <strong>d</strong>, <strong>i</strong>, <strong>o</strong>, <strong>u</strong>, <strong>x</strong>, or <strong>X</strong> conversion corresponds to a
              <em>short</em> <em>int</em> or <em>unsigned</em> <em>short</em> <em>int</em> argument, or that a
              following  <strong>n</strong> conversion corresponds to a pointer to
              a <em>short</em> <em>int</em> argument.

       <strong>o</strong>      The optional character <strong>l</strong> (ell)  specifying  that  a
              following <strong>d</strong>, <strong>i</strong>, <strong>o</strong>, <strong>u</strong>, <strong>x</strong>, or <strong>X</strong> conversion applies to
              a pointer to a <em>long</em> <em>int</em> or <em>unsigned</em> <em>long</em> <em>int</em>  argu-
              ment,  or that a following <strong>n</strong> conversion corresponds
              to a pointer to a <em>long</em> <em>int</em> argument.

       <strong>o</strong>      The character <strong>L</strong> specifying that a following  <strong>e</strong>,  <strong>E</strong>,
              <strong>f</strong>,  <strong>g</strong>, or <strong>G</strong> conversion corresponds to a <em>long</em> <em>double</em>
              argument.

       <strong>o</strong>      A character that specifies 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  <em>int</em> argument supplies the field width or precision.  A
       negative field width is treated as a left adjustment  flag
       followed  by  a positive field width; a negative precision
       is treated as though it were missing.

       The conversion specifiers and their meanings are:

       <strong>diouxX</strong> The <em>int</em> (or appropriate variant) argument  is  con-
              verted  to signed decimal (<strong>d</strong> and <strong>i</strong>), unsigned octal
              (<strong>o</strong>, unsigned decimal (<strong>u</strong>, or unsigned hexadecimal (<strong>x</strong>
              and <strong>X</strong>) notation.  The letters <strong>abcdef</strong> are used for <strong>x</strong>
              conversions; the letters <strong>ABCDEF</strong> are used for <strong>X</strong> con-
              versions.  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.

       <strong>DOU</strong>    The <em>long</em> <em>int</em> argument is converted to signed  deci-
              mal, unsigned octal, or unsigned decimal, as if the
              format had been <strong>ld</strong>, <strong>lo</strong>, or <strong>lu</strong> respectively.   These
              conversion  characters  are  deprecated,  and  will
              eventually disappear.

       <strong>eE</strong>     The <em>double</em> argument is rounded and converted in the
              style  [-]d<strong>.</strong>ddd<strong>e</strong>dd  where there is one digit before
              the decimal-point character and the number of  dig-
              its after it is equal to the precision; if the pre-
              cision is missing, it is taken as 6; if the  preci-
              sion  is  zero, no decimal-point character appears.
              An <strong>E</strong> conversion uses the letter <strong>E</strong> (rather  than  <strong>e</strong>)
              to  introduce  the  exponent.   The exponent always
              contains at least two digits; if the value is zero,
              the exponent is 00.

       <strong>f</strong>      The  <em>double</em>  argument  is  rounded and converted to
              decimal notation in the style [-]ddd<strong>.</strong>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.

       <strong>g</strong>      The <em>double</em> argument is converted in style  <strong>f</strong>  or  <strong>e</strong>
              (or  <strong>E</strong> for <strong>G</strong> 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 <strong>e</strong> 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  fol-
              lowed by at least one digit.

       <strong>c</strong>      The  <em>int</em> argument is converted to an <em>unsigned</em> <em>char</em>,
              and the resulting character is written.

       <strong>s</strong>      The ``<em>char</em> <em>*</em>'' 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 <strong>NUL</strong> character;
              if a precision is specified, no more than the  num-
              ber  specified  are  written.   If  a  precision is
              given, no null character need be  present;  if  the
              precision  is not specified, or is greater than the
              size of the array, the array must contain a  termi-
              nating <strong>NUL</strong> character.

       <strong>p</strong>      The  ``<em>void</em> <em>*</em>'' pointer argument is printed in hex-
              adecimal (as if by <strong>%#x</strong> or <strong>%#lx</strong>).

       <strong>n</strong>      The number of characters written so far  is  stored
              into  the  integer  indicated  by the ``<em>int</em> <em>*</em>'' (or
              variant) pointer argument.   No  argument  is  con-
              verted.

       <strong>%</strong>      A  `%'  is  written.  No argument is converted. The
              complete conversion specification is `%%'.

       In no case does a non-existent 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  con-
       tain the conversion result.

EXAMPLES

To  print  a  date  and  time in the form `Sunday, July 3,
       10:02', where <em>weekday</em> and <em>month</em> are pointers to strings:
              #include &lt;stdio.h&gt;
              fprintf(stdout, &quot;%s, %s %d, %.2d:%.2dn&quot;,
                   weekday, month, day, hour, min);

       To print to five decimal places:
              #include &lt;math.h&gt;
              #include &lt;stdio.h&gt;
              fprintf(stdout, &quot;pi = %.5fn&quot;, 4 * atan(1.0));

       To allocate a 128 byte string and print into it:
              #include &lt;stdio.h&gt;
              #include &lt;stdlib.h&gt;
              #include &lt;stdarg.h&gt;
              char *newfmt(const char *fmt, ...)
              {
                        char *p;
                        va_list ap;
                        if ((p = malloc(128)) == NULL)
                             return (NULL);
                        va_start(ap, fmt);
                        (void) vsnprintf(p, 128, fmt, ap);
                        va_end(ap);
                        return (p);
              }

SEE ALSO

<strong><a href="http://man.he.net/man1/printf">printf(1)</a></strong>, <strong><a href="http://man.he.net/man3/scanf">scanf(3)</a></strong>

STANDARDS

The  <strong>fprintf</strong>,  <strong>printf</strong>,  <strong>sprintf</strong>,  <strong>vprintf</strong>,  <strong>vfprintf</strong>,  and
       <strong>vsprintf</strong>  functions  conform  to  ANSI C3.159-1989 (``ANSI
       C'').

BUGS

Some floating point conversions under Linux  cause  memory
       leaks.

       The conversion formats <strong>%D</strong>, <strong>%O</strong>, and <strong>%U</strong> are not standard and
       are provided only for backward compatibility.   These  may
       not be provided under Linux.

       The  effect of padding the <strong>%p</strong> format with zeros (either by
       the <strong>0</strong> flag or by specifying a precision), and  the  benign
       effect  (i.e.,  none)  of  the <strong>#</strong> flag on <strong>%n</strong> and <strong>%p</strong> conver-
       sions, as well as other nonsensical combinations  such  as
       <strong>%Ld</strong>,   are  not  standard;  such  combinations  should  be
       avoided.

       Because <strong>sprintf</strong> and <strong>vsprintf</strong>  assume  an  infinitely  long
       string, callers must be careful not to overflow the actual
       space; this is often impossible to assure.

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