String formatting with printf:

Problems.

• How can I print out a text table?
• How can I format numbers with only 2 decimals?
• How can I pad a number to fixed with putting zeros in front of it?
• ...

Solution. These and more little everyday problems can be solved with String>>printf: . See the examples below.

"to use :printf you must load this package"
 Feature require:'Printf'

 ". print an integer"
 'a number : %d' printf: 123.  " 'a number : 123' "
 
 ". pad an integer with starting zeros to make it a deault lenght"
 'padding a number: %05d' printf: 123. "=> 'padding a number: 00123' "
 
 ". print a floating point with as many decimals you wish"
 '3 decimals: %.3f' printf: 123.456789.    "=> '3 decimals: 123.456' "
 
 ". fixed length strings, good for tables "
 '%15s %15s %10s' printf: {'Name'. 'Last name'. 'mail'}. 
"=> '           Name       Last name       mail' "
 
 ". fixed length strings, align left, good for tables "
 '%-15s %-15s %-10s' printf: {'Name'. 'Last name'. 'mail'}. 
"=> 'Name            Last name       mail      ' "
 
 ". BROKEN-at-2025-05-05 --- classic newline "
 'line1\nline2' printf: nil. "=> 'line1
 line2' "

• Thousand separators and locales

". print an integer with thousand separators "
'%_d' printf: {1234}.       "=> '1_234' "
 
". print a float number with default thousand separator, tested for %f and %d. "  
'%_0.2f' printf: {1234.567}.     "=>  '1_234.56'  "
 
". Change format for thousand separator and decimal separator "   
PrintfNumberFormatDescriptor setUserThousandSeparatorTo: $, .  
'%_0.2f' printf: {1234.567}.  "=> '1,234.56' " 
 
 ". now let's print the number in the way it is considered 'normal' in Italy, for example "   
 PrintfNumberFormatDescriptor setUserThousandSeparatorTo: $. .  
 PrintfNumberFormatDescriptor setUserDecimalSeparatorTo: $, .  
 '%_0.2f' printf: {1234.567}.   "=> '1.234,56' "
 
 ". and let's put back the default configuaration "   
 PrintfNumberFormatDescriptor setUserThousandSeparatorTo: nil .  
 PrintfNumberFormatDescriptor setUserDecimalSeparatorTo: nil .  
 '_0.2f' printf: {1234.567}.   "=> '1_234.56' " 

Things that still do not work or are not implemented

• Formatting a number in scientific notation: `%e`, `%E`, `%g`.

"?scientifig notation -- broken ?"  
'scientific: %e' printf: 123345.1234.  "=> 'scientific: 123345.1' "

• Formatting a number in scientific notation: `%e`, `%E`, `%g`.

"?scientifig notation -- broken ?" 
'scientific: %e' printf: 123345.1234. "=> 'scientific: 123345.1' "

• Formatting a long number splitting it on thousands %'.
• Align a string the center of a fixed space. (this is not available in C but it would be nice to have)

---

Dr. Nicola Mingotti last checked on 05-May-2025. Tested in Cuis rolling release.