crypt
hemanman at gmail dot com, the problem is that func() doesn't actually return a value (string or otherwise), so the result of echoing func() is null.
With the comma version, each argument is evaluated and echoed in turn: first the literal string (simple), then func(). Evaluating a function call obviously calls the function (and in this case executes its own internal echo), and the result (null) is then echoed accordingly. So we end up with "outside func() within func()" as we would expect.
Thus:
<?
echo "outside func ()\n", func ();
?>
effectively becomes:
<?
echo "outside func ()\n";
//func ()
{
echo "within func ()\n";
}
echo '';
?>
The dot version is different: there's only one argument here, and it has to be fully evaluated before it can be echoed as requested. So we start at the beginning again: a literal string, no problem, then a concatenator, then a function call. Obviously the function call has to be evaluated before the result can be concatenated with the literal string, and THAT has to happen BEFORE we can complete the echo command. But evaluating func() produces its own call to echo, which promptly gets executed.
Thus:
<?
echo "outside func ()\n" . func ();
?>
effectively becomes:
<?
//func ()
{
echo "within func ()\n";
}
echo "outside func ()\n" . '';
?>
echo
(PHP 4, PHP 5)
echo — Vytisknout jeden nebo více řetězců
Popis
void echo ( string $arg1 [, string $...] )Vytiskne všechny parametry.
echo() vlastně není funkce (je to jazykový konstrukt), takže u něj nemusíte používat závorky. Opravdu, pokud byste potřebovali vytisknout více než jeden parametr, nemohli byste dokonce závorky vůbec použít. Proto nelze použít echo() ani pro proměnnou funkci, ovšem místo toho můžete použít funkci print().
Příklad 2084. Ukázka echo()
<?php
echo "Nazdar světe";
echo "Toto zabírá
několik řádků. Konce řádků se
vytisknou také";
echo "Toto zabírá\nněkolik řádků. Konce řádků se\nvytisknou také.";
echo "Speciální znaky předřazené zpětnými lomítky lze použít i v řetězci \"jako toto\".";
//Proměnné lze použít i uvnitř příkazu echo
$foo = "foobar";
$bar = "barbaz";
echo "foo je $foo"; // foo je foobar
// Použitím jednoduchých uvozovek vypíšte jméno proměnné, nikoli její hodnotu
echo 'foo je $foo'; // foo je $foo
// Jestliže nepotřebujete vypisovat další znaky, můžete rovnou uvést jen názvy proměnných
echo $foo; // foobar
echo $foo, $bar; // foobarbarbaz
echo <<<END
Toto používá "dokumentovou" syntaxi pro víceřádkový výstup
s vložnými $prommenymi. Uvědomte si, že ukončovací řetězec
se středníkem musí být na začátku nového řádku (bez mezer či
tabulátorů).
END;
// Protože echo není funkce, následující kód je neplatný
($some_var) ? echo('true'): echo('false');
// Nicméně tento příklad fungovat bude
($some_var) ? print('true'): print('false'); // print je funkce
echo $some_var ? 'true': 'false'; // příkaz musíte uvést předtím
?>
echo() také má zkrácenou syntaxi, kdy je možné následně za otvíracím php tagem použít jen znak rovná se.
Mám <?=$foo?> foo.
Poznámka: Tato zkrácená syntaxe bude fungovat pouze jsou-li povoleny zkrácené otvírací php tagy; short_open_tag je nastaveno na "on".
add a note
User Contributed Notesecho
nikolaas dot mennega at links dot com dot au
01-Nov-2007 08:04
01-Nov-2007 08:04
Jason Carlson - SiteSanity
16-May-2005 07:28
16-May-2005 07:28
In response to Ryan's post with his echobig() function, using str_split wastes memory resources for what you are doing.
If all you want to do is echo smaller chunks of a large string, I found the following code to perform better and it will work in PHP versions 3+
<?php
function echobig($string, $bufferSize = 8192)
{
// suggest doing a test for Integer & positive bufferSize
for ($chars=strlen($string)-1,$start=0;$start <= $chars;$start += $bufferSize) {
echo substr($string,$start,$buffer_size);
}
}
?>
ryan at wonko dot com
27-Feb-2005 09:56
27-Feb-2005 09:56
Due to the way TCP/IP packets are buffered, using echo to send large strings to the client may cause a severe performance hit. Sometimes it can add as much as an entire second to the processing time of the script. This even happens when output buffering is used.
If you need to echo a large string, break it into smaller chunks first and then echo each chunk. The following function will do the trick in PHP5:
<?php
function echobig($string, $bufferSize = 8192)
{
$splitString = str_split($string, $bufferSize);
foreach($splitString as $chunk)
echo $chunk;
}
?>
zombie)at(localm)dot(org)
25-Jan-2003 08:26
25-Jan-2003 08:26
[Ed. Note: During normal execution, the buffer (where echo's arguments go) is not flushed (sent) after each write to the buffer. To do that you'd need to use the flush() function, and even that may not cause the data to be sent, depending on your web server.]
Echo is an i/o process and i/o processes are typically time consuming. For the longest time i have been outputting content by echoing as i get the data to output. Therefore i might have hundreds of echoes in my document. Recently, i have switched to concatenating all my string output together and then just doing one echo at the end. This organizes the code more, and i do believe cuts down on a bit of time. Likewise, i benchmark all my pages and echo seems to influence this as well. At the top of the page i get the micro time, and at the end i figure out how long the page took to process. With the old method of "echo as you go" the processing time seemed to be dependent on the user's net connection as well as the servers processing speed. This was probably due to how echo works and the sending of packets of info back and forth to the user. One an one script i was getting .0004 secs on a cable modem, and a friend of mine in on dialup was getting .2 secs. Finally, to test that echo is slow; I built strings of XML and XSLT and used the PHP sablotron functions to do a transformation and return a new string. I then echoed the string. Before the echo, the process time was around .025 seconds and .4 after the echo. So if you are big into getting the actual processing time of your scripts, don't include echoes since they seem to be user dependent. Note that this is just my experience and it could be a fluke.