我有DOMDocument::saveXML()返回的一些XML块。它已经非常缩进，每个级别有两个空格，如下所示：
<?xml version="1.0"?>
<root>
<error>
<a>eee</a>
<b>sd</b>
</error>
</root>
由于无法配置关于缩进字符的DOMDocument（AFAIK），我thought it's possible to run a regular expression并通过将所有两个空格对替换为制表符来更改缩进。这可以通过回调函数（Demo）完成：
$xml_string = $doc->saveXML();
function callback($m)
{
$spaces = strlen($m[0]);
$tabs = $spaces / 2;
return str_repeat("\t", $tabs);
}
$xml_string = preg_replace_callback('/^(?:[ ]{2})+/um', 'callback', $xml_string);
我现在想知道是否可以使用回调函数（并且没有e - 修饰符（EVAL））来执行此操作。有想法的任何正则表达式向导？
答案 0 :(得分：23)
您可以使用\G：
preg_replace('/^ |\G /m', "\t", $string);
使用PHP 5.2和5.4在Win32上获得了一些基准测试并获得了以下结果：
>php -v
PHP 5.2.17 (cli) (built: Jan 6 2011 17:28:41)
Copyright (c) 1997-2010 The PHP Group
Zend Engine v2.2.0, Copyright (c) 1998-2010 Zend Technologies
>php -n test.php
XML length: 21100
Iterations: 1000
callback: 2.3627231121063
\G: 1.4221360683441
while: 3.0971200466156
/e: 7.8781840801239
>php -v
PHP 5.4.0 (cli) (built: Feb 29 2012 19:06:50)
Copyright (c) 1997-2012 The PHP Group
Zend Engine v2.4.0, Copyright (c) 1998-2012 Zend Technologies
>php -n test.php
XML length: 21100
Iterations: 1000
callback: 1.3771259784698
\G: 1.4414191246033
while: 2.7389969825745
/e: 5.5516891479492
令人惊讶的是回调比PHP 5.4中的\G更快（似乎依赖于数据，\G在某些其他情况下更快）。
使用\G /^ |\G /m，比/(?:^|\G) /m快一点。
/(?>^|\G) /m甚至比/(?:^|\G) /m慢。
/u，/S，/X次切换不会明显影响\G效果。
while替换在深度较低时最快（在我的测试中最多约4个缩进，8个空格），但随着深度增加则变慢。
使用了以下代码：
<?php
$base_iter = 1000;
$xml_string = str_repeat(<<<_STR_
<?xml version="1.0"?>
<root>
<error>
<a> eee </a>
<b> sd </b>
<c>
deep
deeper still
deepest !
</c>
</error>
</root>
_STR_
, 100);
//*** while ***
$re = '%# Match leading spaces following leading tabs.
^ # Anchor to start of line.
(\t*) # $1: Preserve any/all leading tabs.
[ ]{2} # Match "n" spaces.
%mx';
function conv_indent_while($xml_string) {
global $re;
while(preg_match($re, $xml_string))
$xml_string = preg_replace($re, "$1\t", $xml_string);
return $xml_string;
}
//*** \G ****
function conv_indent_g($string){
return preg_replace('/^ |\G /m', "\t", $string);
}
//*** callback ***
function callback($m)
{
$spaces = strlen($m[0]);
$tabs = $spaces / 2;
return str_repeat("\t", $tabs);
}
function conv_indent_callback($str){
return preg_replace_callback('/^(?:[ ]{2})+/m', 'callback', $str);
}
//*** callback /e ***
function conv_indent_e($str){
return preg_replace('/^(?: )+/me', 'str_repeat("\t", strlen("$0")/2)', $str);
}
//*** tests
function test2() {
global $base_iter;
global $xml_string;
$t = microtime(true);
for($i = 0; $i < $base_iter; ++$i){
$s = conv_indent_while($xml_string);
if(strlen($s) >= strlen($xml_string))
exit("strlen invalid 2");
}
return (microtime(true) - $t);
}
function test1() {
global $base_iter;
global $xml_string;
$t = microtime(true);
for($i = 0; $i < $base_iter; ++$i){
$s = conv_indent_g($xml_string);
if(strlen($s) >= strlen($xml_string))
exit("strlen invalid 1");
}
return (microtime(true) - $t);
}
function test0(){
global $base_iter;
global $xml_string;
$t = microtime(true);
for($i = 0; $i < $base_iter; ++$i){
$s = conv_indent_callback($xml_string);
if(strlen($s) >= strlen($xml_string))
exit("strlen invalid 0");
}
return (microtime(true) - $t);
}
function test3(){
global $base_iter;
global $xml_string;
$t = microtime(true);
for($i = 0; $i < $base_iter; ++$i){
$s = conv_indent_e($xml_string);
if(strlen($s) >= strlen($xml_string))
exit("strlen invalid 02");
}
return (microtime(true) - $t);
}
echo 'XML length: ' . strlen($xml_string) . "\n";
echo 'Iterations: ' . $base_iter . "\n";
echo 'callback: ' . test0() . "\n";
echo '\G: ' . test1() . "\n";
echo 'while: ' . test2() . "\n";
echo '/e: ' . test3() . "\n";
?>
答案 1 :(得分：4)
首先想到以下简单的解决方案：
$xml_string = str_replace(' ', "\t", $xml_string);
但我认为，您希望将替换限制为仅领先的空白。对于这种情况，您当前的解决方案看起来很干净。也就是说，可以在没有回调或e修饰符的情况下执行此操作，但您需要以递归方式运行它以完成工作：
$re = '%# Match leading spaces following leading tabs.
^ # Anchor to start of line.
(\t*) # $1: Preserve any/all leading tabs.
[ ]{2} # Match "n" spaces.
%umx';
while(preg_match($re, $xml_string))
$xml_string = preg_replace($re, "$1\t", $xml_string);
令人惊讶的是，我的测试表明这几乎是回调方法的两倍。 （我猜对了。）
请注意，Qtax有一个优雅的解决方案，工作正常（我给它+1）。但是，我的基准测试显示它比原始回调方法慢。我认为这是因为表达式/(?:^|\G) /um不允许正则表达式引擎利用模式开头的“锚点”内部优化。 RE引擎被迫针对目标字符串中的每个位置测试模式。对于以^锚点开头的模式表达式，RE引擎只需要检查每一行的开头，以便更快地匹配。
很棒的问题！ 1
我必须道歉，因为我上面的表现陈述错误。我只针对一个（非代表性的）测试文件运行了正则表达式，该文件主要是在前导空格中的选项卡。当针对具有大量前导空格的更现实的文件进行测试时，我的上述递归方法的执行速度明显慢于其他两种方法。
如果有人有兴趣，这里是我用来衡量每个正则表达式的性能的基准脚本：
test.php <?php // test.php 20120308_1200
require_once('inc/benchmark.inc.php');
// -------------------------------------------------------
// Test 1: Recursive method. (ridgerunner)
function tabify_leading_spaces_1($xml_string) {
$re = '%# Match leading spaces following leading tabs.
^ # Anchor to start of line.
(\t*) # $1: Any/all leading tabs.
[ ]{2} # Match "n" spaces.
%umx';
while(preg_match($re, $xml_string))
$xml_string = preg_replace($re, "$1\t", $xml_string);
return $xml_string;
}
// -------------------------------------------------------
// Test 2: Original callback method. (hakre)
function tabify_leading_spaces_2($xml_string) {
return preg_replace_callback('/^(?:[ ]{2})+/um', '_callback', $xml_string);
}
function _callback($m) {
$spaces = strlen($m[0]);
$tabs = $spaces / 2;
return str_repeat("\t", $tabs);
}
// -------------------------------------------------------
// Test 3: Qtax's elegantly simple \G method. (Qtax)
function tabify_leading_spaces_3($xml_string) {
return preg_replace('/(?:^|\G) /um', "\t", $xml_string);
}
// -------------------------------------------------------
// Verify we get the same results from all methods.
$data = file_get_contents('testdata.txt');
$data1 = tabify_leading_spaces_1($data);
$data2 = tabify_leading_spaces_2($data);
$data3 = tabify_leading_spaces_3($data);
if ($data1 == $data2 && $data2 == $data3) {
echo ("GOOD: Same results.\n");
} else {
exit("BAD: Different results.\n");
}
// Measure and print the function execution times.
$time1 = benchmark_12('tabify_leading_spaces_1', $data, 2, true);
$time2 = benchmark_12('tabify_leading_spaces_2', $data, 2, true);
$time3 = benchmark_12('tabify_leading_spaces_3', $data, 2, true);
?>
上面的脚本使用了我之前写的以下方便的小基准测试功能：
benchmark.inc.php <?php // benchmark.inc.php
/*----------------------------------------------------------------------------
function benchmark_12($funcname, $p1, $reptime = 1.0, $verbose = true, $p2 = NULL) {}
By: Jeff Roberson
Created: 2010-03-17
Last edited: 2012-03-08
Discussion:
This function measures the time required to execute a given function by
calling it as many times as possible within an allowed period == $reptime.
A first pass determines a rough measurement of function execution time
by increasing the $nreps count by a factor of 10 - (i.e. 1, 10, 100, ...),
until an $nreps value is found which takes more than 0.01 secs to finish.
A second pass uses the value determined in the first pass to compute the
number of reps that can be performed within the allotted $reptime seconds.
The second pass then measures the time required to call the function the
computed number of times (which should take about $reptime seconds). The
average function execution time is then computed by dividing the total
measured elapsed time by the number of reps performed in that time, and
then all the pertinent values are returned to the caller in an array.
Note that this function is limited to measuring only those functions
having either one or two arguments that are passed by value and
not by reference. This is why the name of this function ends with "12".
Variations of this function can be easily cloned which can have more
than two parameters.
Parameters:
$funcname: String containing name of function to be measured. The
function to be measured must take one or two parameters.
$p1: First argument to be passed to $funcname function.
$reptime Target number of seconds allowed for benchmark test.
(float) (Default=1.0)
$verbose Boolean value determines if results are printed.
(bool) (Default=true)
$p2: Second (optional) argument to be passed to $funcname function.
Return value:
$result[] Array containing measured and computed values:
$result['funcname'] : $funcname - Name of function measured.
$result['msg'] : $msg - String with formatted results.
$result['nreps'] : $nreps - Number of function calls made.
$result['time_total'] : $time - Seconds to call function $nreps times.
$result['time_func'] : $t_func - Seconds to call function once.
$result['result'] : $result - Last value returned by function.
Variables:
$time: Float epoch time (secs since 1/1/1970) or benchmark elapsed secs.
$i: Integer loop counter.
$nreps Number of times function called in benchmark measurement loops.
----------------------------------------------------------------------------*/
function benchmark_12($funcname, $p1, $reptime = 1.0, $verbose = false, $p2 = NULL) {
if (!function_exists($funcname)) {
exit("\n[benchmark1] Error: function \"{$funcname}()\" does not exist.\n");
}
if (!isset($p2)) { // Case 1: function takes one parameter ($p1).
// Pass 1: Measure order of magnitude number of calls needed to exceed 10 milliseconds.
for ($time = 0.0, $n = 1; $time < 0.01; $n *= 10) { // Exponentially increase $nreps.
$time = microtime(true); // Mark start time. (sec since 1970).
for ($i = 0; $i < $n; ++$i) { // Loop $n times. ($n = 1, 10, 100...)
$result = ($funcname($p1)); // Call the function over and over...
}
$time = microtime(true) - $time; // Mark stop time. Compute elapsed secs.
$nreps = $n; // Number of reps just measured.
}
$t_func = $time / $nreps; // Function execution time in sec (rough).
// Pass 2: Measure time required to perform $nreps function calls (in about $reptime sec).
if ($t_func < $reptime) { // If pass 1 time was not pathetically slow...
$nreps = (int)($reptime / $t_func); // Figure $nreps calls to add up to $reptime.
$time = microtime(true); // Mark start time. (sec since 1970).
for ($i = 0; $i < $nreps; ++$i) { // Loop $nreps times (should take $reptime).
$result = ($funcname($p1)); // Call the function over and over...
}
$time = microtime(true) - $time; // Mark stop time. Compute elapsed secs.
$t_func = $time / $nreps; // Average function execution time in sec.
}
} else { // Case 2: function takes two parameters ($p1 and $p2).
// Pass 1: Measure order of magnitude number of calls needed to exceed 10 milliseconds.
for ($time = 0.0, $n = 1; $time < 0.01; $n *= 10) { // Exponentially increase $nreps.
$time = microtime(true); // Mark start time. (sec since 1970).
for ($i = 0; $i < $n; ++$i) { // Loop $n times. ($n = 1, 10, 100...)
$result = ($funcname($p1, $p2)); // Call the function over and over...
}
$time = microtime(true) - $time; // Mark stop time. Compute elapsed secs.
$nreps = $n; // Number of reps just measured.
}
$t_func = $time / $nreps; // Function execution time in sec (rough).
// Pass 2: Measure time required to perform $nreps function calls (in about $reptime sec).
if ($t_func < $reptime) { // If pass 1 time was not pathetically slow...
$nreps = (int)($reptime / $t_func); // Figure $nreps calls to add up to $reptime.
$time = microtime(true); // Mark start time. (sec since 1970).
for ($i = 0; $i < $nreps; ++$i) { // Loop $nreps times (should take $reptime).
$result = ($funcname($p1, $p2)); // Call the function over and over...
}
$time = microtime(true) - $time; // Mark stop time. Compute elapsed secs.
$t_func = $time / $nreps; // Average function execution time in sec.
}
}
$msg = sprintf("%s() Nreps:%7d Time:%7.3f s Function time: %.6f sec\n",
$funcname, $nreps, $time, $t_func);
if ($verbose) echo($msg);
return array('funcname' => $funcname, 'msg' => $msg, 'nreps' => $nreps,
'time_total' => $time, 'time_func' => $t_func, 'result' => $result);
}
?>
当我使用test.php的内容运行benchmark.inc.php时，我得到的结果是：
GOOD: Same results.
tabify_leading_spaces_1() Nreps: 1756 Time: 2.041 s Function time: 0.001162 sec
tabify_leading_spaces_2() Nreps: 1738 Time: 1.886 s Function time: 0.001085 sec
tabify_leading_spaces_3() Nreps: 2161 Time: 2.044 s Function time: 0.000946 sec
结论：我建议使用Qtax的方法。
谢谢Qtax！