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String formatting with printf:

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Dr. Nicola Mingotti edited this page Jan 16, 2022 · 4 revisions

Problem. 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      ' "

". 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 updated on 06-Sep-2021. Tested in Cuis5.0-4834.image.

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