Variable length space using printf

Question

I'm trying to format some printf statements to allow for arbitrary levels of indentation. Ideally I want the following output where "One", "Two", etc are placeholders for variable length log messages.

One
 Two
  Three
 Two
One

I'm working on the variable length spacing required for the indentation, and I know I can do the following:

printf( "%*s", indent_level, "" );

but I'm wondering if there's a way to do it without the second empty string arg.

adamk · Accepted Answer · 2010-07-09 16:54:48Z

18

You can just pass as a parameter what you want to printout:

printf( "%*s", indent_level + strlen(mystr), mystr );

answered Jul 9, 2010 at 16:54

adamk

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7 Comments

bvanvugt Over a year ago

Good suggestion, but the output string is also of variable length: printf( "%*s%d, %d, %d, %s, CONSTANT CHARS, %p\n", indent_level, "", ... ); It's a pain to determine the length of that string without using an intermediate buffer.

adamk Over a year ago

You only have to know the length of the first parameter - e.g. you could use printf("%*d, %d, ...", indent_level, param1, ... )

user319824 Over a year ago

I have first time seing that type usage of printf,can you explain why you are using indent_level+strlen(mystr)?

adamk Over a year ago

From printf's manpage: The field width: An optional decimal digit string (with non-zero first digit) specifying a minimum field width. Instead of a decimal digit string one may write "*" or "*m$" (for some decimal integer m) to specify that the field width is given in the next argument.

bvanvugt Over a year ago

@adamk Hmm, I don't follow how printf( "%*d", indent_level, param ) will do what I want.

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undercat · Accepted Answer · 2012-08-15 10:34:46Z

5

Can't write a comment for some reason, so posting as a separate necro-answer.

>> "Of course, if the first parameter is also variable-length, then this won't work for you"

> Yeah, that's the case; it needs to be able to handle a numeric value as the first param.

You can use a dud string

printf ("%*s%d", indent_level, "", decimal);

in order to indent variable-length decimals. A bit clunky, but works.

answered Aug 15, 2012 at 10:34

undercat

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