Getting the first character of a string with $str[0]

Question

I want to get the first letter of a string and I've noticed that $str[0] works great. I am just not sure whether this is 'good practice', as that notation is generally used with arrays. This feature doesn't seem to be very well documented so I'm turning to you guys to tell me if it's all right – in all respects – to use this notation?

Or should I just stick to the good ol' substr($str, 0, 1)?

Also, I noted that curly braces ($str{0}) works as well. What's up with that?

Solution 1

Yes. Strings can be seen as character arrays, and the way to access a position of an array is to use the [] operator. Usually there's no problem at all in using $str[0] (and I'm pretty sure is much faster than the substr() method).

There is only one caveat with both methods: they will get the first byte, rather than the first character. This is important if you're using multibyte encodings (such as UTF-8). If you want to support that, use mb_substr(). Arguably, you should always assume multibyte input these days, so this is the best option, but it will be slightly slower.

Solution 2

The {} syntax is deprecated as of PHP 5.3.0. Square brackets are recommended.

Solution 3

Lets say you just want the first char from a part of $_POST, lets call it 'type'. And that $_POST['type'] is currently 'Control'. If in this case if you use $_POST['type'][0], or substr($_POST['type'], 0, 1)you will get C back.

However, if the client side were to modify the data they send you, from type to type[] for example, and then send 'Control' and 'Test' as the data for this array, $_POST['type'][0] will now return Control rather than C whereas substr($_POST['type'], 0, 1) will simply just fail.

So yes, there may be a problem with using $str[0], but that depends on the surrounding circumstance.

Solution 4

My only doubt would be how applicable this technique would be on multi-byte strings, but if that's not a consideration, then I suspect you're covered. (If in doubt, mb_substr() seems an obviously safe choice.)

However, from a big picture perspective, I have to wonder how often you need to access the 'n'th character in a string for this to be a key consideration.

Solution 5

In case of multibyte (unicode) strings using str[0] can cause a trouble. mb_substr() is a better solution. For example:

$first_char = mb_substr($title, 0, 1);

Some details here: Get first character of UTF-8 string

View more solutions

Comments

[Máster]

plus 1 for the "good ol' substr($str, 0, 1)" .

[VolkerK]

docs.php.net/language.types.string : Note: Strings may also be accessed using braces, as in $str{42}, for the same purpose. However, this syntax is deprecated as of PHP 5.3.0. Use square brackets instead, such as $str[42].

[Marco Demaio]

@VolkerK: at the link you provided I noticed they removed the note on the PHP manual they left only: Note: Strings may also be accessed using braces, as in $str{42}, for the same purpose. So I'm wondering if they decided that using {} is NOT deprecated anymore as of PHP 6

[Tomer W]

Does PHP $str[0] take into account that there can be 2Byte long chars? UTF and such? (even though substr() does not help with it either!)

[Vic]

If you want to be extra super safe, you should go with mb_substr($str, 0, 1, 'utf-8') so you don't truncate a multibyte string.

[biziclop]

Link to the docs: php.net/manual/en/…

[trante]

Although this is shorter and is easier to remember than substr($str, 0, 1), this confuses who reads the code.

[Tino]

@MarcoDemaio The link now tells the what MichaelMorton says.

[xtempore]

The choice between square-brackets and substr() is largely a matter of preference, but be aware that the result is different when applied to an empty string. If $s = "" then $s[] === "", but substr($s, 0, 1) === false.

[chris]

If $s = "" then $s[0] will generate a "Notice: Uninitialized string offset: 0" whereas substr($s, 0, 1) will not.

[Abhisek Malakar]

I have a problem with such char Arrays. As we can access $str[0], but why we can't access foreach($str as $c)... .

[Will B.]

As a side note to circumvent this particular issue and in either case one should always perform data validation. if (true === is_string($_POST['type']))

[Ellert van Koperen]

Nice test! Some numbers from a 3 year old Xeon: the average float microtime using "array[]" is 2.2427082061768E-7 the average float microtime using "substr()" is 3.9647579193115E-7 the average float microtime using "array{}" is 2.1522283554077E-7

[PypeBros]

for accurate measurements, you should imho better do microtime out of the loop, and don't mix the different approaches within the same loop.

[Willy Stadnick]

@PypeBros can you elaborate about the advantages of your approach and perhaps share the code? thanks

[PypeBros]

assuming that microtime() measures with precision p, that is, microtime() - p < real time < microtime+p, doing before=mt(); 1000_testsA; after=mt() allows you to compute execution of 1 iteration with precision p/1000.

[PypeBros]

not mixing execution of testA and testB within the same loops means you are capable of detecting e.g. the fact that testB is a cache-killer while testA is cache-friendly. When they're both in the same loop, they are measured to have the very same timings because testB polluted testA's caching.

[PypeBros]

similarly, I'd avoid generating strings or randoms within the testing loops and have them ready in an array nearby.

[Mark Amery]

-1; while vague enough that it's not outright false, saying that "Strings can be seen as Char Arrays" is pretty misleading; they have pretty much nothing in common besides being indexable with [0]- or {0}-style indexes. Array functions don't work on strings (nor vica-versa), and the special syntax for appending to arrays ($some_array[] = $new_element) doesn't work on strings.

[Mark Amery]

-1; the OP's question was whether this syntax was a bad practice, and you've responded by... repeating the syntax, without any commentary? This is not an answer.

[Mark Amery]

-1; leaving aside the questionable timing mechanism (it would be better to time many operations than to time them one at a time; I worried upon reading this that just the time taken doing the microtime() call would make up most of the time difference, although experimentally that seems to not be true), there's no reason to care about the tiny speed difference here. It's a fraction of a millionth of a second; when is this ever going to matter?

[Mark Amery]

No, a string is not an array of characters (at least as PHP uses those two terms). -1.

[gattsbr]

@MarkAmery 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. Internally, PHP strings are byte arrays.

[Mark Amery]

@gattsbr internally they are, but as far as the model that PHP exposes goes, they're a fundamentally different thing. Accessing an offset using square bracket notation is pretty much the only operation that they have in common with arrays; string functions don't work on arrays, nor vica versa, and the array append syntax ($arr[] = $new_element) doesn't work on strings. As such, I don't think conceiving of strings as character arrays is useful.

[gattsbr]

@markamery better get on rewriting the php.net manual then to include such a minuscule technicality.

[VolkerK]

"gives no indication of deprecation" - Indeed, the deprecation message has been removed in revision 304518 - The curly-brackets-string-index-accessor-syntax does not emit any deprecation notice, although the original notice have been on and off for PHP 5.x, it does not in the current version, thrus we should not label it as deprecated. Related to bug #52254 - svn.php.net/repository/phpdoc/en/trunk/language/types/…

[Fr0zenFyr]

Any proof of concept and citation for Strings can be seen as character arrays? I don't find array functions working for String!! EDIT: just noticed that @MarkAmery already pointed that out. However, a citation is still needed.

[Odin Thunder]

Can we use array_shift($string) to get the first char?

[Odin Thunder]

No, we can`t :)

[Fr0zenFyr]

As of today (10th May'18), a quote from the liked PHP docs: Note: Strings may also be accessed using braces, as in $str{42}, for the same purpose. Seems like this syntax is going to stay for a while.

[SunB]

Thank you for this solution! if the first character is unicode, [] wont work

[RobinHood70]

And it's been updated again. It's now deprecated as of PHP 7.4.0 and removed in 8.0.0.