substr_count()

(PHP 4, PHP 5, PHP 7)

计算字串出现的次数

说明

substr_count(string $haystack, string $needle[,int $offset= 0[,int $length]]) : int

substr_count()返回子字符串$needle在字符串$haystack中出现的次数。注意$needle区分大小写。

Note:
该函数不会计算重叠字符串。参见下面的例子。

参数

$haystack: 在此字符串中进行搜索。
$needle: 要搜索的字符串。
$offset: 开始计数的偏移位置。如果是负数，就从字符的末尾开始统计。
$length: 指定偏移位置之后的最大搜索长度。如果偏移量加上这个长度的和大于$haystack的总长度，则打印警告信息。负数的长度 length 是从$haystack的末尾开始统计的。

返回值

该函数返回整型。

更新日志

版本	说明
7.1.0	开始支持负数的`$offset`和`$length`。
5.1.0	新增`$offset`和`$length`参数。

范例

Example #1substr_count()范例

<?php
$text = 'This is a test';
echo strlen($text); // 14
echo substr_count($text, 'is'); // 2
// 字符串被简化为 's is a test'，因此输出 1
echo substr_count($text, 'is', 3);
// 字符串被简化为 's i'，所以输出 0
echo substr_count($text, 'is', 3, 3);
// 因为 5+10 > 14，所以生成警告
echo substr_count($text, 'is', 5, 10);
// 输出 1，因为该函数不计算重叠字符串
$text2 = 'gcdgcdgcd';
echo substr_count($text2, 'gcdgcd');
?>

参见

count_chars()返回字符串所用字符的信息
strpos()查找字符串首次出现的位置
substr()返回字符串的子串
strstr()查找字符串的首次出现

It's worth noting this function is surprisingly fast. I first ran it against a ~500KB string on our web server. It found 6 occurrences of the needle I was looking for in 0.0000 seconds. Yes, it ran faster than microtime() could measure.
Looking to give it a challenge, I then ran it on a Mac laptop from 2010 against a 120.5MB string. For one test needle, it found 2385 occurrences in 0.0266 seconds. Another test needs found 290 occurrences in 0.114 seconds.
Long story short, if you're wondering whether this function is slowing down your script, the answer is probably not.

Making this case insensitive is easy for anyone who needs this. Simply convert the haystack and the needle to the same case (upper or lower).
substr_count(strtoupper($haystack), strtoupper($needle))

It was suggested to use
substr_count ( implode( $haystackArray ), $needle );
instead of the function described previously, however this has one flaw. For example this array:
array (
 0 => "mystringth",
 1 => "atislong"
);
If you are counting "that", the implode version will return 1, but the function previously described will return 0.

To account for the case that jrhodes has pointed out, we can change the line to:
substr_count ( implode( ',', $haystackArray ), $needle );
This way:
array (
 0 => "mystringth",
 1 => "atislong"
);
Becomes
mystringth,atislong
Which brings the count for $needle = "that" to 0 again.

a simple version for an array needle (multiply sub-strings):
<?php
function substr_count_array( $haystack, $needle ) {
   $count = 0;
   foreach ($needle as $substring) {
     $count += substr_count( $haystack, $substring);
   }
   return $count;
}
?>

Yet another reference to the "cgcgcgcgcgcgc" example posted by "chris at pecoraro dot net":
Your request can be fulfilled with the Perl compatible regular expressions and their lookahead and lookbehind features.
The example
 $number_of_full_pattern = preg_match_all('/(cgc)/', "cgcgcgcgcgcgcg", $chunks);
works like the substr_count function. The variable $number_of_full_pattern has the value 3, because the default behavior of Perl compatible regular expressions is to consume the characters of the string subject that were matched by the (sub)pattern. That is, the pointer will be moved to the end of the matched substring.
But we can use the lookahead feature that disables the moving of the pointer:
 $number_of_full_pattern = preg_match_all('/(cg(?=c))/', "cgcgcgcgcgcgcg", $chunks);
In this case the variable $number_of_full_pattern has the value 6.
Firstly a string "cg" will be matched and the pointer will be moved to the end of this string. Then the regular expression looks ahead whether a 'c' can be matched. Despite of the occurence of the character 'c' the pointer is not moved.

This will handle a string where it is unknown if comma or period are used as thousand or decimal separator. Only exception where this leads to a conflict is when there is only a single comma or period and 3 possible decimals (123.456 or 123,456). An optional parameter is passed to handle this case (assume thousands, assume decimal, decimal when period, decimal when comma). It assumes an input string in any of the formats listed below.
function toFloat($pString, $seperatorOnConflict="f")
{
  $decSeperator=".";
  $thSeperator="";
  $pString=str_replace(" ", $thSeperator, $pString);
  $firstPeriod=strpos($pString, ".");
  $firstComma=strpos($pString, ",");
  if($firstPeriod!==FALSE && $firstComma!==FALSE) {
    if($firstPeriod<$firstComma) {
      $pString=str_replace(".", $thSeperator, $pString);
      $pString=str_replace(",", $decSeperator, $pString);
    }
    else {
      $pString=str_replace(",", $thSeperator, $pString);
    }
  }
  else if($firstPeriod!==FALSE  ||  $firstComma!==FALSE) {
    $seperator=$firstPeriod!==FALSE?".":",";
    if(substr_count($pString, $seperator)==1) {
      $lastPeriodOrComma=strpos($pString, $seperator);
      if($lastPeriodOrComma==(strlen($pString)-4) && ($seperatorOnConflict!=$seperator && $seperatorOnConflict!="f")) {
        $pString=str_replace($seperator, $thSeperator, $pString);
      }
      else {
        $pString=str_replace($seperator, $decSeperator, $pString);
      }
    }
    else {
      $pString=str_replace($seperator, $thSeperator, $pString);
    }
  }
  return(float)$pString;
}
function testFloatParsing() { 
  $floatvals = array( 
    "22 000", 
    "22,000", 
    "22.000", 
    "123 456",
    "123,456",
    "123.456",
    "22 000,76", 
    "22.000,76", 
    "22,000.76", 
    "22000.76", 
    "22000,76", 
    "1.022.000,76", 
    "1,022,000.76", 
    "1,000,000", 
    "1.000.000", 
    "1022000.76", 
    "1022000,76", 
    "1022000", 
    "0.76", 
    "0,76", 
    "0.00", 
    "0,00", 
    "1.00", 
    "1,00", 
    "-22 000,76", 
    "-22.000,76", 
    "-22,000.76", 
    "-22 000", 
    "-22,000", 
    "-22.000", 
    "-22000.76", 
    "-22000,76", 
    "-1.022.000,76", 
    "-1,022,000.76", 
    "-1,000,000", 
    "-1.000.000", 
    "-1022000.76", 
    "-1022000,76", 
    "-1022000", 
    "-0.76", 
    "-0,76", 
    "-0.00", 
    "-0,00", 
    "-1.00", 
    "-1,00" 
  ); 
  
  echo "<table> 
    <tr> 
      <th>String</th> 
      <th>thousands</th> 
      <th>fraction</th> 
      <th>dec. if period</th> 
      <th>dec. if comma</th> 
    </tr>"; 
    
  foreach ($floatvals as $fval) { 
    echo "<tr>"; 
    echo "<td>" . (string) $fval . "</td>"; 
    
    echo "<td>" . (float) toFloat($fval, "") . "</td>"; 
    echo "<td>" . (float) toFloat($fval, "f") . "</td>"; 
    echo "<td>" . (float) toFloat($fval, ".") . "</td>"; 
    echo "<td>" . (float) toFloat($fval, ",") . "</td>"; 
    echo "</tr>"; 
  } 
  echo "</table>"; 
}

below was suggested a function for substr_count'ing an array, yet for a simpler procedure, use the following:
<?php
substr_count ( implode( $haystackArray ), $needle );
?>

Unicode example with "case-sensitive" option;
<?php
function substr_count_unicode($str, $substr, $caseSensitive = true, $offset = 0, $length = null) {
  if ($offset) {
    $str = substr_unicode($str, $offset, $length);
  }
  $pattern = $caseSensitive
    ? '~(?:'. preg_quote($substr) .')~u'
    : '~(?:'. preg_quote($substr) .')~ui';
  preg_match_all($pattern, $str, $matches);
  return isset($matches[0]) ? count($matches[0]) : 0;
}
function substr_unicode($str, $start, $length = null) {
  return join('', array_slice(
    preg_split('~~u', $str, -1, PREG_SPLIT_NO_EMPTY), $start, $length));
}
$s = 'Ümit yüzüm gözüm...';
print substr_count_unicode($s, 'ü');      // 3
print substr_count_unicode($s, 'ü', false);   // 4
print substr_count_unicode($s, 'ü', false, 10); // 1
print substr_count_unicode($s, 'üm');      // 2
print substr_count_unicode($s, 'üm', false);  // 3
?>

In regards to anyone thinking of using code contributed by zmindster at gmail dot com
Please take careful consideration of possible edge cases with that regex, in example:
$url = 'http://w3.host.tld/path/to/file/..../file.extension';
$url = 'http://w3.host.tld/path/to/file/../file.extension?malicous=....';
This would cause a infinite loop and for example be a possible entry point for a denial of service attack. A correct fix would require additional code, a quick hack would be just adding a additional check, without clarity or performance in mind:
...
$i = 0;
while (substr_count($url, '../') && ++$i < strlen($url))
...
-Chris