System.Text.StringBuilder和Java的java.lang.StringBuilder。// This...
echo 'one', 'two';
// Is the same as this
echo 'one';
echo 'two';
// This...
echo 'one', 'two';
// Is faster than this...
echo 'one' . 'two';
$values = array( 'one', 'two', 'three' );
$valueList = implode( ', ', $values );
我对此很好奇，所以我进行了一项测试。我使用了以下代码：
<?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);
通过图表可以看出，使用sprintf来进行格式化输出是时间和内存消耗最高的方法。
test2，但将.替换为,（当然不使用输出缓冲区）。 - Raptor在PHP中，不需要StringBuilder类的模拟。
我进行了几个简单的测试：
在PHP中：
$iterations = 10000;
$stringToAppend = 'TESTSTR';
$timer = new Timer(); // based on microtime()
$s = '';
for($i = 0; $i < $iterations; $i++)
{
$s .= ($i . $stringToAppend);
}
$timer->VarDumpCurrentTimerValue();
$timer->Restart();
// Used purlogic's implementation.
// I tried other implementations, but they are not faster
$sb = new StringBuilder();
for($i = 0; $i < $iterations; $i++)
{
$sb->append($i);
$sb->append($stringToAppend);
}
$ss = $sb->toString();
$timer->VarDumpCurrentTimerValue();
在 C# (.NET 4.0) 中：
const int iterations = 10000;
const string stringToAppend = "TESTSTR";
string s = "";
var timer = new Timer(); // based on StopWatch
for(int i = 0; i < iterations; i++)
{
s += (i + stringToAppend);
}
timer.ShowCurrentTimerValue();
timer.Restart();
var sb = new StringBuilder();
for(int i = 0; i < iterations; i++)
{
sb.Append(i);
sb.Append(stringToAppend);
}
string ss = sb.ToString();
timer.ShowCurrentTimerValue();
结果：
10000次迭代：
1）PHP，普通连接：约6毫秒
2）PHP，使用StringBuilder：约5毫秒
3）C＃，普通连接：约520毫秒
4）C＃，使用StringBuilder：约1毫秒
100000次迭代：
1）PHP，普通连接：约63毫秒
2）PHP，使用StringBuilder：约555毫秒
3）C＃，普通连接：约91000毫秒 // !!!
4）C＃，使用StringBuilder：约17毫秒
当你进行定时比较时，差异非常小，这并不太相关。更明智的选择是采用使您的代码更易于阅读和理解的选项。
我知道你在说什么。我刚刚创建了这个简单的类来模拟Java的StringBuilder类。
class StringBuilder {
private $str = array();
public function __construct() { }
public function append($str) {
$this->str[] = $str;
}
public function toString() {
return implode($this->str);
}
}
append函数的结尾处，您可以添加return $this;以允许方法链接：$sb->append("one")->append("two");。 - JabbaPHP字符串是可变的。您可以像这样更改特定字符：
$string = 'abc';
$string[2] = 'a'; // $string equals 'aba'
$string[3] = 'd'; // $string equals 'abad'
$string[5] = 'e'; // $string equals 'abad e' (fills character(s) in between with spaces)
您可以像这样将字符附加到字符串中：
$string .= 'a';
$OneMB=str_repeat('x', 1024*1024);
$Final=$OneMB.$OneMB.$OneMB.$OneMB.$OneMB;
print memory_get_peak_usage();
结果=10,806,800字节（约10MB，不包括初始PHP内存占用）
$OneMB=str_repeat('x', 1024*1024);
$Final=implode('', Array($OneMB, $OneMB, $OneMB, $OneMB, $OneMB));
print memory_get_peak_usage();
结果=6,613,320字节（~6MB，不包括PHP的初始内存占用）
因此，在非常大的字符串连接中，实际上存在可能相当显著的差异（我在创建非常大的数据集或SQL查询时遇到过这种情况）。
但是，即使是这个事实也是有争议的，具体取决于数据。例如，将1个字符连接到字符串上以获得50百万字节（因此需要5000万次迭代）最多需要50,322,512字节（约48MB），用时5.97秒。而使用数组方法则需要7,337,107,176字节（约6.8GB）来创建数组，用时12.1秒，然后再花费额外的4.32秒将字符串从数组中组合起来。
总之...以下是我在开头提到的基准代码，它显示了这些方法基本上是相等的。它输出一个漂亮的HTML表格。
<?
//Please note, for the recursion test to go beyond 256, xdebug.max_nesting_level needs to be raised. You also may need to update your memory_limit depending on the number of iterations
//Output the start memory
print 'Start: '.memory_get_usage()."B<br><br>Below test results are in MB<br>";
//Our 1MB string
global $OneMB, $NumIterations;
$OneMB=str_repeat('x', 1024*1024);
$NumIterations=500;
//Run the tests
$ConcatTest=RunTest('ConcatTest');
$ImplodeTest=RunTest('ImplodeTest');
$RecurseTest=RunTest('RecurseTest');
//Output the results in a table
OutputResults(
Array('ConcatTest', 'ImplodeTest', 'RecurseTest'),
Array($ConcatTest, $ImplodeTest, $RecurseTest)
);
//Start a test run by initializing the array that will hold the results and manipulating those results after the test is complete
function RunTest($TestName)
{
$CurrentTestNums=Array();
$TestStartMem=memory_get_usage();
$StartTime=microtime(true);
RunTestReal($TestName, $CurrentTestNums, $StrLen);
$CurrentTestNums[]=memory_get_usage();
//Subtract $TestStartMem from all other numbers
foreach($CurrentTestNums as &$Num)
$Num-=$TestStartMem;
unset($Num);
$CurrentTestNums[]=$StrLen;
$CurrentTestNums[]=microtime(true)-$StartTime;
return $CurrentTestNums;
}
//Initialize the test and store the memory allocated at the end of the test, with the result
function RunTestReal($TestName, &$CurrentTestNums, &$StrLen)
{
$R=$TestName($CurrentTestNums);
$CurrentTestNums[]=memory_get_usage();
$StrLen=strlen($R);
}
//Concatenate 1MB string over and over onto a single string
function ConcatTest(&$CurrentTestNums)
{
global $OneMB, $NumIterations;
$Result='';
for($i=0;$i<$NumIterations;$i++)
{
$Result.=$OneMB;
$CurrentTestNums[]=memory_get_usage();
}
return $Result;
}
//Create an array of 1MB strings and then join w/ an implode
function ImplodeTest(&$CurrentTestNums)
{
global $OneMB, $NumIterations;
$Result=Array();
for($i=0;$i<$NumIterations;$i++)
{
$Result[]=$OneMB;
$CurrentTestNums[]=memory_get_usage();
}
return implode('', $Result);
}
//Recursively add strings onto each other
function RecurseTest(&$CurrentTestNums, $TestNum=0)
{
Global $OneMB, $NumIterations;
if($TestNum==$NumIterations)
return '';
$NewStr=RecurseTest($CurrentTestNums, $TestNum+1).$OneMB;
$CurrentTestNums[]=memory_get_usage();
return $NewStr;
}
//Output the results in a table
function OutputResults($TestNames, $TestResults)
{
global $NumIterations;
print '<table border=1 cellspacing=0 cellpadding=2><tr><th>Test Name</th><th>'.implode('</th><th>', $TestNames).'</th></tr>';
$FinalNames=Array('Final Result', 'Clean');
for($i=0;$i<$NumIterations+2;$i++)
{
$TestName=($i<$NumIterations ? $i : $FinalNames[$i-$NumIterations]);
print "<tr><th>$TestName</th>";
foreach($TestResults as $TR)
printf('<td>%07.4f</td>', $TR[$i]/1024/1024);
print '</tr>';
}
//Other result numbers
print '<tr><th>Final String Size</th>';
foreach($TestResults as $TR)
printf('<td>%d</td>', $TR[$NumIterations+2]);
print '</tr><tr><th>Runtime</th>';
foreach($TestResults as $TR)
printf('<td>%s</td>', $TR[$NumIterations+3]);
print '</tr></table>';
}
?>
我刚遇到了这个问题：
$str .= '字符串连接。';
vs.
$str = $str . '字符串连接。';
迄今为止似乎没有人在这里进行过比较。使用50,000次迭代和PHP 7.4，结果相当惊人：
字符串1：0.0013918876647949
字符串2：1.1183910369873
倍数：803 !!!
$currentTime = microtime(true);
$str = '';
for ($i = 50000; $i > 0; $i--) {
$str .= 'String concatenation. ';
}
$currentTime2 = microtime(true);
echo "String 1: " . ( $currentTime2 - $currentTime);
$str = '';
for ($i = 50000; $i > 0; $i--) {
$str = $str . 'String concatenation. ';
}
$currentTime3 = microtime(true);
echo "<br>String 2: " . ($currentTime3 - $currentTime2);
echo "<br><br>Faktor: " . (($currentTime3 - $currentTime2) / ( $currentTime2 - $currentTime));
有人能确认这个吗？我遇到了这个问题，因为我在读取大文件时删除了一些行，只将想要的行附加到一个字符串中。
使用“.=”解决了我这里所有的问题。之前我会超时！
echo str1，str2，str3
而不是
echo str1.str2.str3以获得更快的速度。
echo $a,$b,$c;
比
echo $a . $b . $c;
然而，在PHP5中，字符串连接非常快，特别是如果对于给定的字符串只有一个引用。我猜解释器在内部使用了类似于StringBuilder的技术。
$x = 5; echo "x = $x";会输出x = 5，而$x = 5; echo 'x = $x';则会输出x = $x。 - samitny