$str = substr("HomePage", 4, 4);
substrの第一引数は元の文字列、第二引数は取り出し開始位置、第三引数は取り出す文字数です。結果は、$strが'Page'となります。
出典(authority):フリー百科事典『ウィキペディア(Wikipedia)』「2013/08/22 10:46:51」(JST)
A subsequence, substring, prefix or suffix of a string is a subsequence of the symbols in a string, where the order of the elements is preserved. In this context, the terms string and sequence have the same meaning.
A subsequence of a string is a string such that , where . Subsequence is a generalisation of substring, suffix and prefix. Finding the longest string which is equal to a subsequence of two or more strings is known as the longest common subsequence problem.
Example: The string anna
is equal to a subsequence of the string banana
:
banana || || an na
Including the empty subsequence, the number of subsequences of a string of length where symbols only occur once, is simply the number of subsets of the symbols indices, i.e. .
A substring (or factor) of a string is a string , where and . A substring of a string is a prefix of a suffix of the string, and equivalently a suffix of a prefix. If is a substring of , it is also a subsequence, which is a more general concept. Given a pattern , you can find its occurrences in a string with a string searching algorithm. Finding the longest string which is equal to a substring of two or more strings is known as the longest common substring problem.
Example: The string ana
is equal to substrings (and subsequences) of banana
at two different offsets:
banana ||||| ana|| ||| ana
In the mathematical literature, substrings are also called subwords (in America) or factors (in Europe).
Not including the empty substring, the number of substrings of a string of length where symbols only occur once, is the number of ways to choose two distinct places between symbols to start/end the substring. Including the very beginning and very end of the string, there are such places. So there are non-empty substrings.
A prefix of a string is a string , where . A proper prefix of a string is not equal to the string itself ();[1] some sources[2] in addition restrict a proper prefix to be non-empty (). A prefix can be seen as a special case of a substring.
Example: The string ban
is equal to a prefix (and substring and subsequence) of the string banana
:
banana ||| ban
The square subset symbol is sometimes used to indicate a prefix, so that denotes that is a prefix of . This defines a binary relation on strings, called the prefix relation.
In formal language theory, the term prefix of a string is also commonly understood to be the set of all prefixes of a string, with respect to that language. See the article on string functions for more details.
A suffix of a string is a string , where . A proper suffix of a string is not equal to the string itself (); again, a more restricted interpretation is that it is also not empty[1] (). A suffix can be seen as a special case of a substring.
Example: The string nana
is equal to a suffix (and substring and subsequence) of the string banana
:
banana |||| nana
A suffix tree for a string is a trie data structure that represents all of its suffixes. Suffix trees have large numbers of applications in string algorithms. The suffix array is a simplified version of this data structure that lists the start positions of the suffixes in alphabetically sorted order; it has many of the same applications.
A border is suffix and prefix of the same string, e.g. "bab" is a border of "babab".
Given a set of strings , a superstring of the set is single string that contains every string in as a substring. For example, a concatenation of the strings of in any order gives a trivial superstring of . For a more interesting example, let . Then is a superstring of , and is another, shorter superstring of . Generally, we are interested in finding superstrings whose length is small.[clarification needed]
リンク元 | 「mb substr」「str replace」 |
拡張検索 | 「substrata」 |
string mb_substr ( string $str , int $start [, int $length [, string $encoding ]] ) 文字数に基づきマルチバイト対応の substr() 処理を行います。位置は、 str の始めから数えられます。 最初の文字の位置は 0、2 番目の文字の位置は 1、といったようになります。
$subject = "2013内科"; $work = mb_substr($subject, 0, 4,"SJIS"); 文字コードを指定しないとマトモに文字を拾えない $work = mb_substr($subject, 4, 65535 ,"SJIS"); 3番目の添え字は省略する方法が分からないので、思い切り大きい数を指定したが
$str = 'ABCDEFGH'; $str2 = str_replace("CD", "cd", $str);
str_replaceの第一引数は置換対象の文字列、第二引数は置換後の文字列、第三引数は元の文字列です。結果は、$str2が'ABcdDEFH'となります。
.