Question

I’m working through some more PHP tutorials, specifically DevZone PHP 101, and am confused by:

echo .sprintf("%4.2f", (2 * $radius * pi()))

I found this

I think that means produce a floating-point field four positions wide with two decimal places, using the value of the first succeeding parameter.

That comes from the C/C++ line of programming languages. an sprintf() takes the first parameter as a format statement. Anything in it starting with a % is a field specifier; anything else is just printable text. So if you give a format statement with all text and no specifiers, it will print exactly the way it appears. With format specifiers, it needs data to work on.

But after trying some different values I’m still not getting it. It seems to me if the purpose of it in this case is just to limit the decimal to 2 places all I have to put is

.sprintf("%.2f", (2 * $radius * pi()))

What is the point of the 4 in the front of it? In the PHP Manual it leads me to believe it determines the total number of characters should be 4 but (a) thats not the case since the decimal point makes it 5 characters and (b) thats not the case because I tried changing it to a larger number like %8.2f and it didn’t tack any zeros on to either end. Could someone please better explain this.

Thanks!

Answer 1

The first number %8.2f in the format specifier is for the filling length. Per default sprintf uses the space character.

You can see the effect with larger numbers:

printf("%20.2f", 1.23);

Will for example lead to:

                1.23

There’s 16 spaces before the number. The float takes up 4, and the fill length was set to 20 for instance. (Maybe you printed it out into the webpage, thus no padding spaces were visible..)

And there’s an example further below on the sprintf manpage to use alternative padding characters:

printf("%'*20.2f", 1.23); // use the custom padding character '*'

Will result in:

****************1.23