CODEWITHSUNDEEP
c++regex
sohel14_cse_ju
sohel14_cse_ju

Reputation: 2521

Regular Expression Valid and Invalid togather

I the below items i want to only detect the valid items with regular expression. Space in word means invalid, # sign means invalid, Starting word with number is invalid.

Invalid : M_123 ASD
Invalid : M_123#ASD
Invalid : 1_M# ADD
Valid : M_125ASD
Valid : M_125$ASD

I am trying as below :

[A-Za-z0-9_$]

Not working properly. I need to set both valid and invalid sets for a word.

Can i do a match with regular expression?

Upvotes: 1

Views: 237

Answers (2)

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 627327

Your regex [A-Za-z0-9_$] presents a character class that matches a single character that is either an ASCII letter or digit, or _ or $ symbols. If you use it with std::regex_match, it would only match a whole string that consists of just one char like that since the pattern is anchored by default when used with that method. If you use it with an std::regex_search, a string like ([_]) would pass, since the regex is not anchored and can find partial matches.

To match 0 or more chars, you need to add * quantifier after your class. To match one or more chars, you need to add + quantifier after your character class. However, you have an additional restriction: a digit cannot appear at the start.

It seems you may use 

^[A-Za-z][A-Za-z0-9_$]*$

See the regex demo at regex101.com.

Details:

  • ^ - start of string
  • [A-Za-z] - an ASCII letter (exactly one occurrence)
  • [A-Za-z0-9_$]* - 0+ ASCII letters, digits, _ or $
  • $ - end of string anchor.

Note that with regex_match, you may omit ^ and $ anchors.

Upvotes: 1

Abdul Hameed
Abdul Hameed

Reputation: 992

So the requirements are

  • cannot start with number( i am assuming it as start with alphabet)

  • cannot contain space or #

  • all other characters are valid

you can try this regex ^[a-zA-Z]((?![\# ]).)+?$

^[a-zA-Z] checks for alphabet at start of the line ((?![\# ]).)+?$ checks if there are no # or space in the remaining part of the line.

Online demo here

EDIT

As per Wiktor's comment the regex can be simplified to ^[a-zA-Z][^# ]+$.

Upvotes: 0

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