distrib/share/tcl/help/tcl/strings/format

   1 NAME
   2        format - Format a string in the style of sprintf
   3
   4 SYNOPSIS
   5        format formatString ?arg arg ...?
   6
   7
   8 INTRODUCTION
   9        This command generates a formatted string in the same way as the ANSI C
  10        sprintf procedure (it uses sprintf  in  its  implementation).   Format-
  11        String  indicates  how  to format the result, using % conversion speci-
  12        fiers as in sprintf, and the additional arguments, if any, provide val-
  13        ues to be substituted into the result.  The return value from format is
  14        the formatted string.
  15
  16 DETAILS ON FORMATTING
  17        The command operates by scanning formatString from left to right.  Each
  18        character  from  the  format  string  is  appended to the result string
  19        unless it is a percent sign.  If the character is a % then  it  is  not
  20        copied  to  the result string.  Instead, the characters following the %
  21        character are treated as a conversion specifier.  The conversion speci-
  22        fier controls the conversion of the next successive arg to a particular
  23        format and the result is appended to the result string in place of  the
  24        conversion  specifier.   If there are multiple conversion specifiers in
  25        the format string, then each one controls the conversion of  one  addi-
  26        tional  arg.   The format command must be given enough args to meet the
  27        needs of all of the conversion specifiers in formatString.
  28
  29        Each conversion specifier may contain up to  six  different  parts:  an
  30        XPG3  position specifier, a set of flags, a minimum field width, a pre-
  31        cision, a length modifier, and a conversion character.   Any  of  these
  32        fields  may be omitted except for the conversion character.  The fields
  33        that are present must appear in the order given above.  The  paragraphs
  34        below discuss each of these fields in turn.
  35
  36        If  the % is followed by a decimal number and a $, as in ``%2$d'', then
  37        the value to convert is not taken from the  next  sequential  argument.
  38        Instead, it is taken from the argument indicated by the number, where 1
  39        corresponds to the first arg.  If  the  conversion  specifier  requires
  40        multiple  arguments  because of * characters in the specifier then suc-
  41        cessive arguments are used, starting with the  argument  given  by  the
  42        number.   This  follows the XPG3 conventions for positional specifiers.
  43        If there are any positional specifiers in formatString then all of  the
  44        specifiers must be positional.
  45
  46        The  second  portion  of  a conversion specifier may contain any of the
  47        following flag characters, in any order:
  48
  49        -         Specifies that the converted argument should  be  left-justi-
  50                  fied  in its field (numbers are normally right-justified with
  51                  leading spaces if needed).
  52
  53        +         Specifies that a number should always be printed with a sign,
  54                  even if positive.
  55
  56        space     Specifies  that  a  space should be added to the beginning of
  57                  the number if the first character isn't a sign.
  58
  59        0         Specifies that the number should be padded on the  left  with
  60                  zeroes instead of spaces.
  61
  62        #         Requests an alternate output form. For o and O conversions it
  63                  guarantees that the first digit is always 0.  For x or X con-
  64                  versions, 0x or 0X (respectively) will be added to the begin-
  65                  ning of the result unless it is zero.  For all floating-point
  66                  conversions (e, E, f, g, and G) it guarantees that the result
  67                  always has a decimal point.  For g and G conversions it spec-
  68                  ifies that trailing zeroes should not be removed.
  69
  70        The  third portion of a conversion specifier is a number giving a mini-
  71        mum field width for this conversion.  It is typically used to make col-
  72        umns  line up in tabular printouts.  If the converted argument contains
  73        fewer characters than the minimum field width then it will be padded so
  74        that it is as wide as the minimum field width.  Padding normally occurs
  75        by adding extra spaces on the left of the converted argument, but the 0
  76        and  -  flags may be used to specify padding with zeroes on the left or
  77        with spaces on the right, respectively.  If the minimum field width  is
  78        specified as * rather than a number, then the next argument to the for-
  79        mat command determines the minimum field width; it must  be  a  numeric
  80        string.
  81
  82        The fourth portion of a conversion specifier is a precision, which con-
  83        sists of a period followed by a number.  The number is used in  differ-
  84        ent  ways  for  different  conversions.  For e, E, and f conversions it
  85        specifies the number of digits to appear to the right  of  the  decimal
  86        point.  For g and G conversions it specifies the total number of digits
  87        to appear, including those on both sides of the decimal point (however,
  88        trailing  zeroes  after  the decimal point will still be omitted unless
  89        the # flag has been specified).  For integer conversions, it  specifies
  90        a  minimum  number  of digits to print (leading zeroes will be added if
  91        necessary).  For s conversions it specifies the maximum number of char-
  92        acters to be printed; if the string is longer than this then the trail-
  93        ing characters will be dropped.  If the precision is specified  with  *
  94        rather  than  a  number  then  the  next argument to the format command
  95        determines the precision; it must be a numeric string.
  96
  97        The fifth part of a conversion specifier is a  length  modifier,  which
  98        must  be h or l.  If it is h it specifies that the numeric value should
  99        be truncated to a 16-bit  value  before  converting.   This  option  is
 100        rarely  useful.   If it is l it specifies that the numeric value should
 101        be (at least) a 64-bit value.  If neither h nor l are present,  numeric
 102        values  are  interpreted  as  being  values  of the width of the native
 103        machine word, as described by tcl_platform(wordSize).
 104
 105        The last thing in a conversion specifier  is  an  alphabetic  character
 106        that determines what kind of conversion to perform.  The following con-
 107        version characters are currently supported:
 108
 109        d         Convert integer to signed decimal string.
 110
 111        u         Convert integer to unsigned decimal string.
 112
 113        i         Convert integer to signed decimal string;   the  integer  may
 114                  either be in decimal, in octal (with a leading 0) or in hexa-
 115                  decimal (with a leading 0x).
 116
 117        o         Convert integer to unsigned octal string.
 118
 119        x or X    Convert integer to unsigned hexadecimal string, using  digits
 120                  ``0123456789abcdef'' for x and ``0123456789ABCDEF'' for X).
 121
 122        c         Convert integer to the Unicode character it represents.
 123
 124        s         No conversion; just insert string.
 125
 126        f         Convert floating-point number to signed decimal string of the
 127                  form xx.yyy, where the number of y's  is  determined  by  the
 128                  precision  (default: 6).  If the precision is 0 then no deci-
 129                  mal point is output.
 130
 131        e or e    Convert floating-point number to scientific notation  in  the
 132                  form x.yyye+-zz, where the number of y's is determined by the
 133                  precision (default: 6).  If the precision is 0 then no  deci-
 134                  mal point is output.  If the E form is used then E is printed
 135                  instead of e.
 136
 137        g or G    If the exponent is less than -4 or greater than or  equal  to
 138                  the  precision,  then convert floating-point number as for %e
 139                  or %E.  Otherwise convert as for %f.  Trailing zeroes  and  a
 140                  trailing decimal point are omitted.
 141
 142        %         No conversion: just insert %.
 143
 144        For  the  numerical conversions the argument being converted must be an
 145        integer or floating-point  string;  format  converts  the  argument  to
 146        binary  and  then converts it back to a string according to the conver-
 147        sion specifier.
 148
 149 DIFFERENCES FROM ANSI SPRINTF
 150        The behavior of the format command is the same as the  ANSI  C  sprintf
 151        procedure except for the following differences:
 152
 153        [1]    %p and %n specifiers are not currently supported.
 154
 155        [2]    For  %c conversions the argument must be a decimal string, which
 156               will then be converted to the corresponding character value.
 157
 158        [3]    The l modifier is ignored for real values and  on  64-bit  plat-
 159               forms,  which  are  always  converted  as if the l modifier were
 160               present (i.e. the types double and long are used for the  inter-
 161               nal  representation  of  real and integer values, respectively).
 162               If the h modifier is specified then integer values are truncated
 163               to  short before conversion.  Both h and l modifiers are ignored
 164               on all other conversions.
 165
 166 EXAMPLES
 167        Convert the output of time into seconds to an accuracy of hundredths of
 168        a second:
 169               set us [lindex [time $someTclCode] 0]
 170               puts [format "%.2f seconds to execute" [expr {$us / 1e6}]]
 171
 172        Create a packed X11 literal color specification:
 173               # Each color-component should be in range (0..255)
 174               set color [format "#%02x%02x%02x" $r $g $b]
 175
 176        Use  XPG3  format codes to allow reordering of fields (a technique that
 177        is often used  in  localized  message  catalogs;  see  msgcat)  without
 178        reordering the data values passed to format:
 179               set fmt1 "Today, %d shares in %s were bought at $%.2f each"
 180               puts [format $fmt1 123 "Global BigCorp" 19.37]
 181
 182               set fmt2 "Bought %2\$s equity ($%3$.2f x %1\$d) today"
 183               puts [format $fmt2 123 "Global BigCorp" 19.37]
 184
 185        Print a small table of powers of three:
 186               # Set up the column widths
 187               set w1 5
 188               set w2 10
 189
 190               # Make a nice header (with separator) for the table first
 191               set sep +-[string repeat - $w1]-+-[string repeat - $w2]-+
 192               puts $sep
 193               puts [format "| %-*s | %-*s |" $w1 "Index" $w2 "Power"]
 194               puts $sep
 195
 196               # Print the contents of the table
 197               set p 1
 198               for {set i 0} {$i<=20} {incr i} {
 199                  puts [format "| %*d | %*ld |" $w1 $i $w2 $p]
 200                  set p [expr {wide($p) * 3}]
 201               }
 202
 203               # Finish off by printing the separator again
 204               puts $sep
 205
 206
 207 SEE ALSO
 208        scan(n), sprintf(3), string(n)
 209
 210
 211 KEYWORDS