Home > Articles > Programming > C/C++

  • Print
  • + Share This
Like this article? We recommend

Some Regular Expression Rules

Since people are familiar with the * and possibly the ? patterns in filename matching, I’ll start with the equivalent in regular expressions. To match any single character in regular expressions (same as the ? in filename matching), you use a single period (.) character. In other words, a single period matches any single character. The following strings (or any other single character) will match the . pattern:

a
b
1
2

Now consider this pattern:

.*

This pattern matches any number of characters, thus behaving similarly to the * pattern. The following strings, for example, will match this pattern:

abc
abc123
123
Four score and seven years ago

As you can, see, any string whatsoever will match this pattern. The idea is that the . character matches any single character, and when you tack on the * character, you’re saying that the . character can be repeated any number of times for a match.

In filename patterns, letters, numbers, and other non-pattern characters (such as everything but the two ? characters in the filename pattern abc??.txt) are called literals. The same is true in regular expressions. Thus, suppose you want a regular expression that works the same way as this filename pattern:

a??c

You would write it like this:

a..c

This pattern matches any string that is four characters long, starts with an a and ends with a c. Here are some strings that would match this pattern:

abcc
a12c
a c

For that last one, that’s two spaces between the a and the c.

Next, consider the following filename pattern:

abc*

This pattern matches any file starting with abc followed by anything whatsoever. Here’s the equivalent regular expression:

abc.*

The following are example strings would match:

abc123
abcxyz
abcz
abc

Notice that any string starting with abc will match, even the string consisting of only abc.

Here’s another example. Consider this pattern:

a.*b

The following are examples of strings that will match this pattern:

ab
a123b
abbbb
axyzb

Again, notice the first example, in which no characters are present between the a and the b. The .* pattern means any characters, including no characters.

Repeating Matches

In the preceding patterns, you may have noticed that unlike with filename patterns, matching more than one character requires two characters in the pattern—the period followed by the asterisk (.*). That’s because the * character means that the preceding character can repeat any number of times (including zero or no times) to get a match.

Regular expressions use various characters to signify repeating matches. While the * character means that a character can match any number of times, including zero, the plus (+) pattern indicates that the preceding pattern must match at least one or more times (but not zero times). Take this pattern, for example:

ab+c

The following strings will match this pattern:

abc
abbc
abbbbbbbbc

But ac will not match because at least one b must be present between a and c. In the case of the pattern ab*c, all of the preceding examples will match, as will ab.

If you want to match a character either zero times or one time (but not more than one) use the ? character. Consider this pattern:

ab?c

Following are the only strings that will match this pattern:

ac
abc

If you want to be absolutely precise, you can specify how many times you allow a character to match. To do so, place opening and closing braces ({}) following the character, and put inside the braces either a number for an exact amount, or two numbers separated by a comma for a range. For example:

ab{10}c

matches b exactly 10 times, and thus only this string will match:

abbbbbbbbbbc

This pattern will match b two, three, four, or five times:

ab{2,5}c

Thus, only these strings will match:

abbc
abbbc
abbbbc
abbbbbc

Treating Special Characters or Literals

What if you want to match an asterisk, a question mark, a period, or any of the special characters? Just put a backslash before it. For example, the following pattern:

a\*b

matches only one string:

a*b

And this pattern:

a\.b*

matches any of the following strings, for example:

a.
a.b
a.bb
a.bbb

Lots More About the Syntax

Perl-style regular expressions can do far more than I’ve described so far. If you want to learn more about the syntax, here are some places to go. First, check out the documentation for the Boost C++ library that I’m going to use in the next section. Next, check out the official Perl documentation on regular expressions. Finally, if you really want to get serious about regular expressions, most people agree that the best book available is Mastering Regular Expressions by Jeffrey Friedl (O’Reilly, 2002).

Now let’s look at some C++ code to implement regular expressions.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020