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format(3tcl) Tcl Built-In Commands format(3tcl) 





NAME


format - Format a string in the style of sprintf






SYNOPSIS


format formatString ?arg arg ...?








INTRODUCTION


This command generates a formatted string in a fashion similar to
    the ANSI C sprintf procedure. FormatString indicates how to
    format the result, using % conversion specifiers as in
    sprintf, and the additional arguments, if any, provide values to be
    substituted into the result. The return value from format is the
    formatted string.






DETAILS ON FORMATTING


The command operates by scanning formatString from left to
    right. Each character from the format string is appended to the result
    string unless it is a percent sign. If the character is a % then it
    is not copied to the result string. Instead, the characters following the
    % character are treated as a conversion specifier. The conversion
    specifier controls the conversion of the next successive arg to a
    particular format and the result is appended to the result string in place
    of the conversion specifier. If there are multiple conversion specifiers in
    the format string, then each one controls the conversion of one additional
    arg. The format command must be given enough args to
    meet the needs of all of the conversion specifiers in
  formatString.


Each conversion specifier may contain up to six different parts:
    an XPG3 position specifier, a set of flags, a minimum field width, a
    precision, a size modifier, and a conversion character. Any of these fields
    may be omitted except for the conversion character. The fields that are
    present must appear in the order given above. The paragraphs below discuss
    each of these fields in turn.




OPTIONAL POSITIONAL SPECIFIER


If the % is followed by a decimal number and a $, as
    in “%2$d”, then the value to convert is not taken from
    the next sequential argument. Instead, it is taken from the argument
    indicated by the number, where 1 corresponds to the first arg. If the
    conversion specifier requires multiple arguments because of *
    characters in the specifier then successive arguments are used, starting
    with the argument given by the number. This follows the XPG3 conventions for
    positional specifiers. If there are any positional specifiers in
    formatString then all of the specifiers must be positional.






OPTIONAL FLAGS


The second portion of a conversion specifier may contain any of
    the following flag characters, in any order:



  
-

  
Specifies that the converted argument should be left-justified in its
      field (numbers are normally right-justified with leading spaces if
      needed).

  
+

  
Specifies that a number should always be printed with a sign, even if
      positive.

  

  
Specifies that a space should be added to the beginning of the number if
      the first character is not a sign.

  
0

  
Specifies that the number should be padded on the left with zeroes instead
      of spaces.

  
#

  
Requests an alternate output form. For o conversions, 0o
      will be added to the beginning of the result unless it is zero. For
      x or X conversions, 0x will be added to the beginning
      of the result unless it is zero. For b conversions, 0b will
      be added to the beginning of the result unless it is zero. For d
      conversions, 0d there is no effect unless the 0 specifier is
      used as well: In that case, 0d will be added to the beginning. For
      all floating-point conversions (e, E, f, g,
      and G) it guarantees that the result always has a decimal point.
      For g and G conversions it specifies that trailing zeroes
      should not be removed.








OPTIONAL FIELD WIDTH


The third portion of a conversion specifier is a decimal number
    giving a minimum field width for this conversion. It is typically used to
    make columns line up in tabular printouts. If the converted argument
    contains fewer characters than the minimum field width then it will be
    padded so that it is as wide as the minimum field width. Padding normally
    occurs by adding extra spaces on the left of the converted argument, but the
    0 and - flags may be used to specify padding with zeroes on
    the left or with spaces on the right, respectively. If the minimum field
    width is specified as * rather than a number, then the next argument
    to the format command determines the minimum field width; it must be
    an integer value.






OPTIONAL PRECISION/BOUND


The fourth portion of a conversion specifier is a precision, which
    consists of a period followed by a number. The number is used in different
    ways for different conversions. For e, E, and f
    conversions it specifies the number of digits to appear to the right of the
    decimal point. For g and G conversions it specifies the total
    number of digits to appear, including those on both sides of the decimal
    point (however, trailing zeroes after the decimal point will still be
    omitted unless the # flag has been specified). For integer
    conversions, it specifies a minimum number of digits to print (leading
    zeroes will be added if necessary). For s conversions it specifies
    the maximum number of characters to be printed; if the string is longer than
    this then the trailing characters will be dropped. If the precision is
    specified with * rather than a number then the next argument to the
    format command determines the precision; it must be a numeric
  string.






OPTIONAL SIZE MODIFIER


The fifth part of a conversion specifier is a size modifier, which
    must be ll, h, l, z, t, or L. If
    it is ll it specifies that an integer value is taken without
    truncation for conversion to a formatted substring. If it is h it
    specifies that an integer value is truncated to a 16-bit range before
    converting. This option is rarely useful. If it is l (or j or
    q) it specifies that the integer value is truncated to the same range
    as that produced by the wide() function of the expr command
    (at least a 64-bit range). If it is z or t it specifies that
    the integer value is truncated to the range determined by the value of the
    pointerSize element of the tcl_platform array. If it is
    L it specifies that an integer or double value is taken without
    truncation for conversion to a formatted substring. If neither of those are
    present, the integer value is truncated to a 32-bit range.






MANDATORY CONVERSION TYPE


The last thing in a conversion specifier is an alphabetic
    character that determines what kind of conversion to perform. The following
    conversion characters are currently supported:



  

  
Convert integer to signed decimal string.

  

  
Convert integer to unsigned decimal string.

  

  
Convert integer to signed decimal string (equivalent to d).

  

  
Convert integer to unsigned octal string.

  

  
Convert integer to unsigned hexadecimal string, using digits
      “0123456789abcdef” for x and
      “0123456789ABCDEF” for X).

  

  
Convert integer to unsigned binary string, using digits 0 and 1.

  

  
Convert integer to the Unicode character it represents.

  

  
No conversion; just insert string.

  

  
Convert number to signed decimal string of the form xx.yyy, where
      the number of y's is determined by the precision (default: 6). If
      the precision is 0 then no decimal point is output.

  

  
Convert number to scientific notation in the form
      x.yyye±zz, where the number of y's is
      determined by the precision (default: 6). If the precision is 0 then no
      decimal point is output. If the E form is used then E is
      printed instead of e.

  

  
If the exponent is less than -4 or greater than or equal to the precision,
      then convert number as for %e or %E. Otherwise convert as
      for %f. Trailing zeroes and a trailing decimal point are
    omitted.

  

  
Convert double to hexadecimal notation in the form
      0x1.yyyp±zz, where the number of y's is
      determined by the precision (default: 13). If the A form is used
      then the hex characters are printed in uppercase.

  
%

  
No conversion: just insert %.

  

  
Shorthand form for 0x%zx, so it outputs the integer in hexadecimal
      form with 0x prefix.










DIFFERENCES FROM ANSI SPRINTF


The behavior of the format command is the same as the ANSI C
    sprintf procedure except for the following differences:



  
[1]

  
Tcl guarantees that it will be working with UNICODE characters.

  
[2]

  
%n specifier is not supported.

  
[3]

  
For %c conversions the argument must be an integer value, which
      will then be converted to the corresponding character value.

  
[4]

  
The size modifiers are ignored when formatting floating-point values. The
      b specifier has no sprintf counterpart.








EXAMPLES


Convert the numeric value of a UNICODE character to the character
    itself:






set value 120
set char [format %c $value]




Convert the output of time into seconds to an accuracy of
    hundredths of a second:






set us [lindex [time $someTclCode] 0]
puts [format "%.2f seconds to execute" [expr {$us / 1e6}]]




Create a packed X11 literal color specification:






# Each color-component should be in range (0..255)
set color [format "#%02x%02x%02x" $r $g $b]




Use XPG3 format codes to allow reordering of fields (a technique
    that is often used in localized message catalogs; see msgcat) without
    reordering the data values passed to format:






set fmt1 "Today, %d shares in %s were bought at $%.2f each"
puts [format $fmt1 123 "Global BigCorp" 19.37]
set fmt2 "Bought %2\$s equity ($%3$.2f x %1\$d) today"
puts [format $fmt2 123 "Global BigCorp" 19.37]




Print a small table of powers of three:






# Set up the column widths
set w1 5
set w2 10
# Make a nice header (with separator) for the table first
set sep +-[string repeat - $w1]-+-[string repeat - $w2]-+
puts $sep
puts [format "| %-*s | %-*s |" $w1 "Index" $w2 "Power"]
puts $sep
# Print the contents of the table
set p 1
for {set i 0} {$i<=20} {incr i} {


    puts [format "| %*d | %*ld |" $w1 $i $w2 $p]


    set p [expr {wide($p) * 3}]
}
# Finish off by printing the separator again
puts $sep








SEE ALSO


scan(3tcl), sprintf(3), string(3tcl)






KEYWORDS


conversion specifier, format, sprintf, string, substitution







  

    8.1
    Tcl