How to format strings using printf to get equal length in the output

Question

I have two functions  one which produces messages like Starting initialization    and another which checks return codes and outputs  quot Ok quot    quot Warning quot  or  quot Error quot   However  the output that is produced is of the different length  Starting initialization   Ok  Checking init scripts   Ok   How can I get something like the following  Starting initialization          Ok  Checking init scripts            Ok

User · Answer

Start with the use of tabs - the  t character modifier  It will advance to a fixed location  columns  terminal lingo   However  it doesn t help if there are differences of more than the column width  4 characters  if I recall correctly   To fix that  write your  quot OK NOK quot  stuff using a fixed number of tabs  5  6   try it   Then return   r  without new-lining  and write your message

User · Answer

There s also the rather low-tech solution of counting adding spaces by hand to make your messages line up  Nothing prevents you from including a few trailing spaces in your message strings

User · Answer

printf allows formatting with width specifiers  For example  printf   quot  -30s  s n quot    quot Starting initialization    quot    quot Ok  quot      You would use a negative width specifier to indicate left-justification because the default is to use right-justification

User · Answer

Additionally  if you want the flexibility of choosing the width  you can choose between one of the following two formats  with or without truncation   int width   30     No truncation uses  - s printf   quot  - s  s n quot   width   quot Starting initialization    quot    quot Ok  quot        Output is  quot Starting initialization        Ok  quot      Truncated to the specified width uses  -  s printf   quot  -  s  s n quot   width   quot Starting initialization    quot    quot Ok  quot        Output is  quot Starting initialization    Ok  quot

User · Answer

You can specify a width on string fields  e g  printf  quot  -20s quot    quot initialization    quot     And then whatever s printed with that field will be blank-padded to the width you indicate  The - left-justifies your text in that field

User · Answer

There s also the  n modifier which can help in certain circumstances  It returns the column on which the string was so far  Example  you want to write several rows that are within the width of the first row like a table  int width1  width2  int values 6  2   printf  quot   s n  s n  n quot   header1   amp width1  header2   amp width2    for i 0  i lt 6  i       printf  quot    d   d  n quot   width1  values i  0   width2  values i  1     will print two columns of the same width of whatever length the two strings header1 and header2 may have  I don t know if all implementations have the  n  but Solaris and Linux do

[c] How to format strings using printf() to get equal length in the output

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