substr_compare()

(PHP 5, PHP 7)

二进制安全比较字符串（从偏移位置比较指定长度）

说明

substr_compare(string $main_str, string $str, int $offset[,int $length[,bool $case_insensitivity= FALSE]]) : int

substr_compare()从偏移位置$offset开始比较$main_str与$str，比较长度为$length个字符。

参数

$main_str

待比较的第一个字符串。

$str

待比较的第二个字符串。

$offset

比较开始的位置。如果为负数，则从字符串结尾处开始算起。

$length

比较的长度。默认值为$str的长度与$main_str的长度减去位置偏移量$offset后二者中的较大者。

$case_insensitivity

如果$case_insensitivity为TRUE，比较将不区分大小写。

返回值

如果$main_str从偏移位置$offset起的子字符串小于$str，则返回小于 0 的数；如果大于$str，则返回大于 0 的数；如果二者相等，则返回 0。如果$offset大于等于$main_str的长度或$length被设置为小于 1 的值（ PHP 5.5.11 之前的版本），substr_compare()将打印出一条警告信息并且返回FALSE。

更新日志

范例

Example #1substr_compare()范例

<?php
echo substr_compare("abcde", "bc", 1, 2); // 0
echo substr_compare("abcde", "de", -2, 2); // 0
echo substr_compare("abcde", "bcg", 1, 2); // 0
echo substr_compare("abcde", "BC", 1, 2, true); // 0
echo substr_compare("abcde", "bc", 1, 3); // 1
echo substr_compare("abcde", "cd", 1, 2); // -1
echo substr_compare("abcde", "abc", 5, 1); // warning
?>

参见

• strncmp()二进制安全比较字符串开头的若干个字符

When you came to this page, you may have been looking for something a little simpler: A function that can check if a small string exists within a larger string starting at a particular index. Using substr_compare() for this can leave your code messy, because you need to check that your string is long enough (to avoid the warning), manually specify the length of the short string, and like many of the string functions, perform an integer comparison to answer a true/false question.
I put together a simple function to return true if $str exists within $mainStr. If $loc is specified, the $str must begin at that index. If not, the entire $mainStr will be searched.
<?php
function contains_substr($mainStr, $str, $loc = false) {
  if ($loc === false) return (strpos($mainStr, $str) !== false);
  if (strlen($mainStr) < strlen($str)) return false;
  if (($loc + strlen($str)) > strlen($mainStr)) return false;
  return (strcmp(substr($mainStr, $loc, strlen($str)), $str) == 0);
}
?>

This function efficiently implements checks for strings beginning or ending with other strings:
<?php
function str_begins($haystack, $needle) {
 return 0 === substr_compare($haystack, $needle, 0, strlen($needle));
}
function str_ends($haystack, $needle) {
 return 0 === substr_compare($haystack, $needle, -strlen($needle));
}
var_dump(str_begins('http://example.com', 'https://'));
?>
Note that these are not multi-byte character set aware.

Take note of the `length` parameter: "The default value is the largest of the length of the str compared to the length of main_str less the offset."
This is *not* the length of str as you might (I always) expect, so if you leave it out, you'll get unexpected results. Example:
<?php
$hash = '$5$lalalalalalalala$crypt.output.here';
var_dump(substr_compare($hash, '$5$', 0)); # int(34)
var_dump(substr_compare($hash, '$5$', 0, 3)); # int(0)
var_dump(PHP_VERSION); # string(6) "5.3.14"
?>

Modified version of the original posted function. Use this one:
<?php
if (!function_exists('substr_compare')) {
  function substr_compare($main_str, $str, $offset, $length = NULL, $case_insensitivity = false) {
    $offset = (int) $offset;
    // Throw a warning because the offset is invalid
    if ($offset >= strlen($main_str)) {
      trigger_error('The start position cannot exceed initial string length.', E_USER_WARNING);
      return false;
    }
    // We are comparing the first n-characters of each string, so let's use the PHP function to do it
    if ($offset == 0 && is_int($length) && $case_insensitivity === true) {
      return strncasecmp($main_str, $str, $length);
    }
    // Get the substring that we are comparing
    if (is_int($length)) {
      $main_substr = substr($main_str, $offset, $length);
      $str_substr = substr($str, 0, $length);
    } else {
      $main_substr = substr($main_str, $offset);
      $str_substr = $str;
    }
    // Return a case-insensitive comparison of the two strings
    if ($case_insensitivity === true) {
      return strcasecmp($main_substr, $str_substr);
    }
    // Return a case-sensitive comparison of the two strings
    return strcmp($main_substr, $str_substr);
  }
}
?>