IOS development-how to use regular expressions, ios Regular Expressions

IOS development-how to use regular expressions, ios Regular Expressions

Regular Expressions are often used in Form Verification, because we need to use them to determine whether the characters entered by users are valid. If they are invalid, the user input error should be prompted and not submitted to the server. You can also use a regular expression to filter and obtain the specific part of the string you want. In short, regular expressions are very powerful.

 

 

Method 1: Create a regular expression using a predicate (NSPredicate)

It is used to determine whether the string entered by the user is legal:

// Write a regular expression: it can only be a number or English, or both have NSString * regex = @ "^ [a-z0-9A-Z] * $ "; // create a predicate object and set the condition expression NSPredicate * predicate = [NSPredicate predicateWithFormat: @ "self matches % @", regex]; // The determined string NSString * str = @ "Hello100"; // if ([predicate evaluateWithObject: str]) {NSLog (@ "Match ");}

The string Hello100 is compliant with the rule, so this example outputs "Match" in the log ". If we replace "Hello100" with other characters (for example, "-, ="), the above example will not output anything.

 

 

MethodIi. Create a regular expression in the NSRegularExpression class

As mentioned in the preface, we can use regular expressions to filter and obtain the specific part we want. The implementation method is also very simple. NSRegularExpression can be used for implementation:

NSString * url = @ "1229436624@qq.com"; NSError * error; // create an NSRegularExpression object and specify the regular expression NSRegularExpression * regex = [NSRegularExpression regularExpressionWithPattern: @ "[^ @] * \. "options: 0 error: & error]; if (! Error) {// if no error exists // obtain the NSTextCheckingResult * match = [regex firstMatchInString: url options: 0 range: NSMakeRange (0, [url length])]; if (match) {// captures a specific string NSString * result = [url substringWithRange: match. range]; NSLog (@ "% @", result) ;}} else {// if an error occurs, print the error to NSLog (@ "error-% @", error );}

In this example, the string is retrieved starting with "@". "The end of the interval string, and the end of the last retrieved string includes". ", so the final output result of this example is" qq."

 

 

MethodIii. NSRegularExpression class capturing multiple results

When a string contains multiple characters that conform to specific rules, we can obtain the characters that comply with specific rules respectively:

NSString * regex = @ "\-\ d *\\. "; NSString * str = @"-34023242. -34203020. "; NSError * error; NSRegularExpression * regular = [NSRegularExpression regularExpressionWithPattern: regex options: Internal error: & error]; // match the str string NSArray * matches = [regular matchesInString: str options: 0 range: NSMakeRange (0, str. length)]; // traverse each matched record for (NSTextCheckingResult * match in matches) {nsange range = [match range]; NSString * mStr = [str substringWithRange: range]; NSLog (@ "% @", mStr );}

Obtain the string starting with "-" And starting with ". ", because there may be multiple strings that comply with specific rules, we need to traverse them. The specific output result is as follows:

[1748:467732] -34023242.[1748:467732] -34203020. 

 

 

Conclusion: Generally, you only need to use method 1 to determine whether the characters entered by the user are valid. If you want to capture the specific content entered by the user, use method 2 or method 3. If there may be multiple capture results, use method 3. Otherwise, use method 2.

 

 

The following are some metacharacters of the regular expression:

Metacharacters	Description
\	Mark the next character as a special character, a literal character, or a backward reference, or an octal escape character. For example, "\ n" matches \ n. "\ N" matches the line break. The sequence "\" matches "\", and "\ (" matches "(".
^	Matches the start position of the input string. If the Multiline attribute of the RegExp object is set, ^ matches the position after "\ n" or "\ r.
$	Matches the end position of the input string. If the Multiline attribute of the RegExp object is set, $ also matches the position before "\ n" or "\ r.
*	Match the previous subexpression zero or multiple times (greater than or equal to 0 times ). For example, zo * can match "z", "zo", and "zoo ". * Is equivalent to {0 ,}.
+	Match the previous subexpression once or multiple times (greater than or equal to 1 time ). For example, "zo +" can match "zo" and "zoo", but cannot match "z ". + Is equivalent to {1 ,}.
?	Match the previous subexpression zero or once. For example, "do (es )?" It can match "do" in "do" or "does ".? It is equivalent to {0, 1 }.
{N}	N is a non-negative integer. Match n times. For example, "o {2}" cannot match "o" in "Bob", but can match two o in "food.
{N ,}	N is a non-negative integer. Match at least n times. For example, "o {2,}" cannot match "o" in "Bob", but can match all o in "foooood. "O {1,}" is equivalent to "o + ". "O {0,}" is equivalent to "o *".
{N, m}	Both m and n are non-negative integers, where n <= m. Match at least n times and at most m times. For example, "o {1, 3}" matches the first three o in "fooooood. "O {0, 1}" is equivalent to "o ?". Note that there must be no space between a comma and two numbers.
?	When this character is followed by any other delimiter (*, + ,?, The matching mode after {n}, {n ,}, {n, m}) is not greedy. The non-Greedy mode matches as few searched strings as possible, while the default greedy mode matches as many searched strings as possible. For example, for strings "oooo", "o + ?" A single "o" will be matched, while "o +" will match all "o ".
.	Match any single character except "\ r \ n. To match any character including "\ r \ n", use a pattern like "[\ s \ S.
(Pattern)	Match pattern and obtain this match. The obtained match can be obtained from the generated Matches set. The SubMatches set is used in VBScript, and $0… is used in JScript... $9 attribute. To match the parentheses, use "\ (" or "\)".
(? : Pattern)	Matches pattern but does not get the matching result. That is to say, this is a non-get match and is not stored for future use. This is useful when you use the "(|)" character to combine all parts of a pattern. For example, "industr (? : Y | ies) "is a simpler expression than" industry | industrial.
(? = Pattern)	Forward validation pre-query: matches the search string at the beginning of any string that matches pattern. This is a non-get match, that is, the match does not need to be obtained for future use. For example (? = 95 | 98 | NT | 2000) "can match" Windows "in" Windows2000 ", but cannot match" Windows "in" Windows3.1 ". Pre-query does not consume characters, that is, after a match occurs, the next matching search starts immediately after the last match, instead of starting after the pre-query characters.
(?! Pattern)	Forward negative pre-query: matches the search string at the beginning of any string that does not match pattern. This is a non-get match, that is, the match does not need to be obtained for future use. For example, "Windows (?! 95 | 98 | NT | 2000) "can match" Windows "in" Windows3.1 ", but cannot match" Windows "in" Windows2000 ".
(? <= Pattern)	The reverse direction must be pre-check, which is similar to positive pre-check, but in the opposite direction. For example, <= 95 | 98 | NT | 2000) Windows can match Windows in 2000Windows, but cannot match Windows in 3.1Windows ".
(? <! Pattern)	Reverse negative pre-query, similar to forward negative pre-query, is in the opposite direction. For example, "(? <! 95 | 98 | NT | 2000) Windows can match "Windows" in "3.1Windows", but cannot match "Windows" in "2000Windows ".
X | y	Match x or y. For example, "z | food" can match "z" or "food ". "(Z | f) ood" matches "zood" or "food ".
[Xyz]	Character Set combination. Match any character in it. For example, "[abc]" can match "a" in "plain ".
[^ Xyz]	Negative value character set combination. Match any character not included. For example, "[^ abc]" can match "plin" in "plain ".
[A-z]	Character range. Matches any character in the specified range. For example, "[a-z]" can match any lowercase letter in the range of "a" to "z. Note: only when a hyphen is in a character group and appears between two characters can the range of the characters be expressed. If a group starts with a hyphen, it can only represent the character itself.
[^ A-z]	Negative character range. Matches any character that is not within the specified range. For example, "[^ a-z]" can match any character that is not in the range of "a" to "z.
\ B	Match A Word boundary, that is, the position between a word and a space. For example, "er \ B" can match "er" in "never", but cannot match "er" in "verb ".
\ B	Match non-word boundary. "Er \ B" can match "er" in "verb", but cannot match "er" in "never ".
\ Cx	Match the control characters specified by x. For example, \ cM matches a Control-M or carriage return character. The value of x must be either a A-Z or a-z. Otherwise, c is treated as a literal "c" character.
\ D	Match a numeric character. It is equivalent to [0-9].
\ D	Match a non-numeric character. It is equivalent to [^ 0-9].
\ F	Match a form feed. It is equivalent to \ x0c and \ cL.
\ N	Match A linefeed. It is equivalent to \ x0a and \ cJ.
\ R	Match a carriage return. It is equivalent to \ x0d and \ cM.
\ S	Matches any blank characters, including spaces, tabs, and page breaks. It is equivalent to [\ f \ n \ r \ t \ v].
\ S	Match any non-blank characters. It is equivalent to [^ \ f \ n \ r \ t \ v].
\ T	Match a tab. It is equivalent to \ x09 and \ cI.
\ V	Match a vertical tab. It is equivalent to \ x0b and \ cK.
\ W	Match any word characters that contain underscores. It is equivalent to "[A-Za-z0-9 _]".
\ W	Match any non-word characters. It is equivalent to "[^ A-Za-z0-9 _]".
\ Xn	Match n, where n is the hexadecimal escape value. The hexadecimal escape value must be determined by the length of two numbers. For example, "\ x41" matches "". "\ X041" is equivalent to "\ x04 & 1 ". The regular expression can be ASCII encoded.
\ Num	Matches num, where num is a positive integer. References to the obtained matching. For example, "(.) \ 1" matches two consecutive identical characters.
\ N	Identifies an octal escape value or a backward reference. If at least n subexpressions are obtained before \ n, n is backward referenced. Otherwise, if n is an octal digit (0-7), n is an octal escape value.
\ Nm	Identifies an octal escape value or a backward reference. If at least one child expression is obtained before \ nm, the nm is backward referenced. If at least n records are obtained before \ nm, n is a backward reference followed by text m. If none of the preceding conditions are met, if n and m are Octal numbers (0-7), \ nm matches the octal escape value nm.
\ Nml	If n is an octal number (0-7) and m and l are Octal numbers (0-7), the octal escape value nml is matched.
\ Un	Match n, where n is a Unicode character represented by four hexadecimal numbers. For example, \ u00A9 matches the copyright symbol (& copy ;).
\ <\>	Start (\ <) and end (\>) of the match word (word ). For example, the regular expression \ <the \> can match the "the" in the string "for the wise", but cannot match the "the" in the string "otherwise ". Note: This metacharacter is not supported by all software.
\(\)	Define the expressions between \ (and \) as "group ), and save the characters matching this expression to a temporary region (a regular expression can save up to 9 characters). They can be referenced using the \ 1 to \ 9 symbols.
|	Perform logical "Or" (Or) operations on the two matching conditions. For example, the regular expression (him | her) matches "it belongs to him" and "it belongs to her", but does not match "it belongs to them .". Note: This metacharacter is not supported by all software.
+	Match one or more characters that match exactly before it. For example, the regular expression 9 + matches 9, 99, and 999. Note: This metacharacter is not supported by all software.
?	Match 0 or 1 character that is exactly before it. Note: This metacharacter is not supported by all software.
{I} {I, j}	Matches a specified number of characters defined in the previous expression. For example, the regular expression A [0-9] {3} can match the character "A" followed by A string of exactly three numeric characters, such as A123 and A348, but does not match A1234. The regular expression [0-9] {} matches any four, five, or six consecutive numbers.

From Baidu Encyclopedia: Regular Expression

 

 

Blog Author: GarveyCalvin

Blog Source: http://www.cnblogs.com/GarveyCalvin/

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