Question

I’ve came across an example in print manual of php.net. that stats.

   echo 3 . print(2) . print(4) . 5 . 'c' . 
   print(6) . print(7). 'b' .print(8) . 'a';

which prints 8a7b16145c12131. But how?

Answer 1

I think you just got fooled by presence of concatenation operator . which made you assume that the only output from this code would come from echo and all other functions would only “contribute” to echo’s argument. It is wrong, of course, because you assumed that print() somehow changed its behaviour and returns its output there, instead of printing it out instantly (upon a call) to the output stream. The only thing you concatenate there are strings and each print()‘s ** return value**. And the latter, according to the manual is always “1”. Change print(), to sprintf() and all the “magic” will be gone.

BTW it is good brainer – can keep busy for a while 🙂

EDIT ON OP’s REQUEST

The “culprit” here is print. It is worth noting that it is not a real function but language construct which influences the way it is handled during evaluation. For example:

echo 3 . print(2) . 'c';

produces:

2c31

But if you move print into function like this:

function x($a) { return print $a; }
echo 3 . x(2) . 'c';

then the output will look more sane:

231c

If you care about details you will need to lurk into Zend Engine sources, but in general, such syntax is likely used for anything useful. Remembering print is tricky suffices.

And why we see “231c” anyway? It is because echo arguments needs first to be evaluated – without that PHP do not really know what to echo (or could know partially). So PHP goes more/less this way:

• get “3” to our temporary string
• call function x(2) – since this function does print, our argument (“2”) will be instantly printed to the output. Function returns “1” because print always return “1” (see manual) so PHP concatenates “1” to so we now have “31”,
• get ‘c’ and concatenate, so we now have “31c”
• echo our temporary string.

Note that in fact echo outputs ’31c’ only. Prefixing “2” is there because it is print output and we had not used LF (or <br /> if you are not testing this in console) in meantime so all output goes into one line. If you change the code to use LF (or <br />):

function x($a) { return print $a; }
$f = 3 . x(2) . 'c';
echo "\n${f}";

then the output will be:

2
31c

Hope this helps.