php String Concatenation, Performance

Question

In languages like Java and C#, strings are immutable and it can be computationally expensive to build a string one character at a time. In said languages, there are library classes to reduce this cost such as C# System.Text.StringBuilder and Java java.lang.StringBuilder.

Does php (4 or 5; I'm interested in both) share this limitation? If so, are there similar solutions to the problem available?

Answer 1

No, there is no type of stringbuilder class in PHP, since strings are mutable.

That being said, there are different ways of building a string, depending on what you're doing.

echo, for example, will accept comma-separated tokens for output.

// This... echo 'one', 'two';  // Is the same as this echo 'one'; echo 'two'; 

What this means is that you can output a complex string without actually using concatenation, which would be slower

// This... echo 'one', 'two';  // Is faster than this... echo 'one' . 'two'; 

If you need to capture this output in a variable, you can do that with the output buffering functions.

Also, PHP's array performance is really good. If you want to do something like a comma-separated list of values, just use implode()

$values = array( 'one', 'two', 'three' ); $valueList = implode( ', ', $values ); 

Lastly, make sure you familiarize yourself with PHP's string type and it's different delimiters, and the implications of each.

Answer 2

I was curious about this, so I ran a test. I used the following code:

<?php ini_set('memory_limit', '1024M'); define ('CORE_PATH', '/Users/foo'); define ('DS', DIRECTORY_SEPARATOR);  $numtests = 1000000;  function test1($numtests) {     $CORE_PATH = '/Users/foo';     $DS = DIRECTORY_SEPARATOR;     $a = array();      $startmem = memory_get_usage();     $a_start = microtime(true);     for ($i = 0; $i < $numtests; $i++) {         $a[] = sprintf('%s%sDesktop%sjunk.php', $CORE_PATH, $DS, $DS);     }     $a_end = microtime(true);     $a_mem = memory_get_usage();      $timeused = $a_end - $a_start;     $memused = $a_mem - $startmem;      echo "TEST 1: sprintf()\n";     echo "TIME: {$timeused}\nMEMORY: $memused\n\n\n"; }  function test2($numtests) {     $CORE_PATH = '/Users/shigh';     $DS = DIRECTORY_SEPARATOR;     $a = array();      $startmem = memory_get_usage();     $a_start = microtime(true);     for ($i = 0; $i < $numtests; $i++) {         $a[] = $CORE_PATH . $DS . 'Desktop' . $DS . 'junk.php';     }     $a_end = microtime(true);     $a_mem = memory_get_usage();      $timeused = $a_end - $a_start;     $memused = $a_mem - $startmem;      echo "TEST 2: Concatenation\n";     echo "TIME: {$timeused}\nMEMORY: $memused\n\n\n"; }  function test3($numtests) {     $CORE_PATH = '/Users/shigh';     $DS = DIRECTORY_SEPARATOR;     $a = array();      $startmem = memory_get_usage();     $a_start = microtime(true);     for ($i = 0; $i < $numtests; $i++) {         ob_start();         echo $CORE_PATH,$DS,'Desktop',$DS,'junk.php';         $aa = ob_get_contents();         ob_end_clean();         $a[] = $aa;     }     $a_end = microtime(true);     $a_mem = memory_get_usage();      $timeused = $a_end - $a_start;     $memused = $a_mem - $startmem;      echo "TEST 3: Buffering Method\n";     echo "TIME: {$timeused}\nMEMORY: $memused\n\n\n"; }  function test4($numtests) {     $CORE_PATH = '/Users/shigh';     $DS = DIRECTORY_SEPARATOR;     $a = array();      $startmem = memory_get_usage();     $a_start = microtime(true);     for ($i = 0; $i < $numtests; $i++) {         $a[] = "{$CORE_PATH}{$DS}Desktop{$DS}junk.php";     }     $a_end = microtime(true);     $a_mem = memory_get_usage();      $timeused = $a_end - $a_start;     $memused = $a_mem - $startmem;      echo "TEST 4: Braced in-line variables\n";     echo "TIME: {$timeused}\nMEMORY: $memused\n\n\n"; }  function test5($numtests) {     $a = array();      $startmem = memory_get_usage();     $a_start = microtime(true);     for ($i = 0; $i < $numtests; $i++) {         $CORE_PATH = CORE_PATH;         $DS = DIRECTORY_SEPARATOR;         $a[] = "{$CORE_PATH}{$DS}Desktop{$DS}junk.php";     }     $a_end = microtime(true);     $a_mem = memory_get_usage();      $timeused = $a_end - $a_start;     $memused = $a_mem - $startmem;      echo "TEST 5: Braced inline variables with loop-level assignments\n";     echo "TIME: {$timeused}\nMEMORY: $memused\n\n\n"; }  test1($numtests); test2($numtests); test3($numtests); test4($numtests); test5($numtests); 

... And got the following results. Image attached. Clearly, sprintf is the least efficient way to do it, both in terms of time and memory consumption. EDIT: view image in another tab unless you have eagle vision.