What does "%.6d" mean in printf

Question

What does %.6d mean in:

printf("%s.%.6d len:%d ", timestr, header->ts.tv_usec, header->len);

Is it a typo?

It seems %.6d is the same as %6d.

Was it really easier/faster to ask this question on SO than to write a quick test program (like the ones in the answers) and run it to see the difference? — tomlogic
– tomlogic, Commented May 6, 2010 at 21:09
You don't even need a program. Just run printf '%.6d\n' 1234 in bash. — Mike DeSimone
– Mike DeSimone, Commented May 7, 2010 at 13:21

codaddict · Accepted Answer · 2010-05-06 06:07:52Z

30

%.6d

In the .precision format for integer specifiers (d, i, o, u, x, X), precision specifies the minimum number of digits to be written. If the value to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer.

%6d

The width (here 6) specifies the minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger.

Example:

printf("%.6d\n%6d",1,1);

outputs:

000001
     1

answered May 6, 2010 at 6:07

codaddict

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3 Comments

user198729 Over a year ago

So it's only different in padding with zeros and blanks?

Mike DeSimone Over a year ago

So %.6d is the same as %06d? Blech, let's hear it for consistency. >_<

Suraj Jain Over a year ago

So is %.6d same as %06d ?

Steve-o · Accepted Answer · 2010-05-06 06:08:51Z

8

The former will pad with zeros, the latter with spaces.

#include <stdio.h>
int main(void) {
    printf ("%.6d\n", 123);
    printf ("%6d\n", 123);
    return 0;
}

Produces the following output,

000123
   123

answered May 6, 2010 at 6:08

Steve-o

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