php 字符串串联，性能

php string concatenation

2022-08-30 08:45:49

在Java和C#等语言中，字符串是不可变的，并且一次构建一个字符的字符串在计算上可能很昂贵。在所述语言中，有库类可以降低这种成本，例如 C#和Java 。System.Text.StringBuilderjava.lang.StringBuilder

做 php （4 或 5;我对两者都感兴趣）分享这个限制？如果是这样，是否有针对该问题的类似解决方案？

答案 1

不，PHP中没有字符串生成器类的类型，因为字符串是可变的。

话虽如此，构建字符串有不同的方法，具体取决于您正在做的事情。

例如，echo 将接受逗号分隔的输出标记。

// This...
echo 'one', 'two';

// Is the same as this
echo 'one';
echo 'two';

这意味着您可以在不实际使用串联的情况下输出复杂的字符串，这会更慢

// This...
echo 'one', 'two';

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

如果需要在变量中捕获此输出，可以使用输出缓冲函数执行此操作。

此外，PHP的数组性能非常好。如果你想做一些类似逗号分隔的值列表，只需使用implode（）

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

最后，请确保您熟悉PHP的字符串类型，它是不同的分隔符，以及每个分隔符的含义。

答案 2

我对此感到好奇，所以我进行了一次测试。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);

...并得到以下结果。附加图像。显然，sprintf是效率最低的方法，无论是在时间还是内存消耗方面。编辑：在另一个选项卡中查看图像，除非您有鹰视觉。 enter image description here