PHP - iterate on string characters

问题:

Is there a nice way to iterate on the characters of a string? I'd like to be able to do foreach, array_map, array_walk, array_filter etc. on the characters of a string.

Type casting/juggling didnt get me anywhere (put the whole string as one element of array), and the best solution I've found is simply using a for loop to construct the array. It feels like there should be something better. I mean, if you can index on it shouldn't you be able to iterate as well?

This is the best I've got

function stringToArray($s)
{
    $r = array();
    for($i=0; $i<strlen($s); $i++) 
         $r[$i] = $s[$i];
    return $r;
}

$s1 = "textasstringwoohoo";
$arr = stringToArray($s1); //$arr now has character array

$ascval = array_map('ord', $arr);  //so i can do stuff like this
$foreach ($arr as $curChar) {....}
$evenAsciiOnly = array_filter( function($x) {return ord($x) % 2 === 0;}, $arr);

Is there either:

A) A way to make the string iterable
B) A better way to build the character array from the string (and if so, how about the other direction?)

I feel like im missing something obvious here.

回答1:

Step 1: convert the string to an array using the str_split function

$array = str_split($your_string);

Step 2: loop through the newly created array

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

You can check the PHP docs for more information: str_split

回答2:

Iterate string:

for ($i = 0; $i < strlen($str); $i++){
    echo $str[$i];
}

回答3:

If your strings are in Unicode you should use preg_split with /u modifier

From comments in php documentation:

function mb_str_split( $string ) { 
    # Split at all position not after the start: ^ 
    # and not before the end: $ 
    return preg_split('/(?<!^)(?!$)/u', $string ); 
} 

回答4:

You can also just access $s1 like an array, if you only need to access it:

$s1 = "hello world";
echo $s1[0]; // -> h

回答5:

Expanded from @SeaBrightSystems answer, you could try this:

$s1 = "textasstringwoohoo";
$arr = str_split($s1); //$arr now has character array

回答6:

For those who are looking for the fastest way to iterate over strings in php, Ive prepared a benchmark testing.
The first method in which you access string characters directly by specifying its position in brackets and treating string like an array:

$string = "a sample string for testing";
$char = $string[4] // equals to m

I myself thought the latter is the fastest method, but I was wrong.
As with the second method (which is used in the accepted answer):

$string = "a sample string for testing";
$string = str_split($string);
$char = $string[4] // equals to m

This method is going to be faster cause we are using a real array and not assuming one to be an array.

Calling the last line of each of the above methods for 1000000 times lead to these benchmarking results:

Using string[i]
0.24960017204285 Seconds

Using str_split
0.18720006942749 Seconds

Which means the second method is way faster.

回答7:

// Unicode Codepoint Escape Syntax in PHP 7.0
$str = "cat!\u{1F431}";

// IIFE (Immediately Invoked Function Expression) in PHP 7.0
$gen = (function(string $str) {
    for ($i = 0, $len = mb_strlen($str); $i < $len; ++$i) {
        yield mb_substr($str, $i, 1);
    }
})($str);

var_dump(
    true === $gen instanceof Traversable,
    // PHP 7.1
    true === is_iterable($gen)
);

foreach ($gen as $char) {
    echo $char, PHP_EOL;
}

回答8:

Hmm... There's no need to complicate things. The basics work great always.

    $string = 'abcdef';
    $len = strlen( $string );
    $x = 0;

Forward Direction:

while ( $len > $x ) echo $string[ $x++ ];

Outputs: abcdef

Reverse Direction:

while ( $len ) echo $string[ --$len ];

Outputs: fedcba