strings in PHP really an array of characters or something else?

Question

Consider

$foo = "abcdefg";

echo $foo[0]; //outputs a

So it seems like strings are like array of characters but then why

foreach($foo as $char)
{
echo $char;
}

does not work and gives following Warning ??

Warning: Invalid argument supplied for foreach()

The old notation (still working but deprecated) was `echo $foo{0};` I never understood why they changed it. — Jacco, Sep 10 '11 at 13:00
@NikiC: Are you triple sure? I was under that same impression. — Jon, Sep 10 '11 at 13:11
@Jon: I am ;) http://codepad.viper-7.com/X0lgFz (It was deprecated a short time during 5.3 development. I don't know why they reverted it, maybe just an accident.) — NikiC, Sep 10 '11 at 13:12
@NikiC: It turns out we are [not imagining things](http://stackoverflow.com/questions/885241/php-string-indexing): looks like this syntax was on its way to being deprecated in PHP 6, but the current doc page has no mention of that. Possibly they changed their mind? — Jon, Sep 10 '11 at 13:19
@Jon Yes, in the sense that we (that is PHP and its community) don't want them to be used. But they are not officially deprecated, sadly :( I'm going to ping internals about getting them deprecated in 5.4 ;) — NikiC, Sep 10 '11 at 13:25
@jacco I just checked it and its working and I will prefer {} over [] with string since it makes me think it as a array :) — Mr Coder, Sep 10 '11 at 13:25
@NikiC, thanks! I will promptly change some of my code back : ) — Jacco, Sep 10 '11 at 14:30
@Jacco Uhm, maybe we have a little misunderstanding here: Even though using curly braces is not deprecated, you should definitely not use them, as it is quite probable that they will get deprecated in later releases ;) — NikiC, Sep 10 '11 at 15:12

NikiC · Accepted Answer · 2011-09-10T13:11:01.013

1

Adding string iteration support to foreach was discussed but declined. There were mainly two reasons for this decision:

It makes applications harder to debug. Usually you don't want to iterate over the characters of a string. You need that only very rarely. So if you do iterate over a string you probably just made a programming mistake - and PHP will tell you so. If string iteration were introduces this kind of error would be hard to catch.
What is a "character"? Should PHP iterate over each single byte? Should it iterate over characters (which can be multiple bytes)? If so, what should it do if it encounters a malformed multibyte sequence? And where does it get the charset from?

To solve both problems there was a proposal to introduce a TextIterator, which you pass a string and a charset. That way you can't accidentally iterate a string and the byte vs character problem doesn't exist. I'm not sure though what the state of the TextIterator is currently.

edited Sep 10 '11 at 13:11

answered Sep 10 '11 at 12:57

NikiC

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TextIterator sounds like a great idea. :) – Herbert Sep 10 '11 at 13:30
it would be cool if PHP interpreter could have taken care of this inside foreach for us now it seems wired to not to think string as array of characters . – Mr Coder Sep 10 '11 at 13:42
You often need to interate by **graphemes** (user-visible characters), not by mere *code point* (programmer-visible character) let alone by uselessly stupid *code units* (computer-visible character). You can use regexes to step through a string a grapheme at a time using `\X`. – tchrist Sep 10 '11 at 19:30
@tchrist: Note though that PHP aint Perl. In PCRE `\X` matches only extended unicode sequences (i.e. a non-mark character followed by an arbitrary number of mark-characters), whereas Perl goes all the way of matching extended grapheme clusters. – NikiC Sep 10 '11 at 20:38

Jon · Answer 2 · 2011-09-10T13:15:14.820

NikiC's answer covers why doing this directly is not possible.

If you want to iterate over a string as if it were an array, you can be explicit by using str_split:

foreach(str_split($foo) as $char) 
{ 
    echo $char; 
}

Warning: str_split is not encoding-aware, so you will end up iterating over bytes and not over characters. Iterating over characters is a little more involved, as there is no equivalent multibyte split function. You can roll your own using the regex-enabled mb_split, look at the comments from PHP.net for ideas.

There are other answers here suggesting you should cast the string to an array, but I don't understand why that would work. The documentation is pretty explicit:

For any of the types: integer, float, string, boolean and resource, converting a value to an array results in an array with a single element with index zero and the value of the scalar which was converted. In other words, (array)$scalarValue is exactly the same as array($scalarValue).

And indeed, doing this does not work as suggested.

score 0 · Answer 3 · answered Sep 10 '11 at 12:57

Even though their characters can be addressed using square brackets, strings aren't arrays. Emphasis mine:

Characters within strings may be accessed and modified by specifying the zero-based offset of the desired character after the string using square array brackets, as in $str[42]. Think of a string as an array of characters for this purpose.

score -1 · Answer 4 · answered Sep 10 '11 at 13:03

-1

it is called "syntax sugar".

For example, in 5.4 you'll be able to do like this echo func()[0];
That doesn't mean that a function is really an array of charactes.
It's just a syntax.

answered Sep 10 '11 at 13:03

Your Common Sense

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strings in PHP really an array of characters or something else?

4 Answers4