Home > Articles > Programming > C/C++

Strong Pointers and Resource Management in C++

Struggling with memory leaks in your program? Having problems with double deletions? In this first article in a two-part series, programming expert Bartosz Milewski describes in detail the resource-management methodology--one of the industrial-strength techniques used in the development of serious C++ applications.
This pair of articles is an edited and extended version of two articles Bartosz Milewski published in C++ Report in September 1998 and February 1999. Bartosz Milewski is the author of C++ In Action: Industrial-Strength Programming Techniques (Addison-Wesley, 2001, ISBN 0-201-69948-6), a book that teaches professional programming in C++.

Resources and Their Ownership

My favorite definition of a resource is "anything that your program has to acquire and then release." Memory is of course the prominent example of a resource. It's acquired using new and released using delete. But there are many other types of resources—file handles, critical sections, GDI resources in Windows, etc. It's convenient to generalize the notion of a resource to encompass all objects created and released in a program, the ones allocated on the heap as well as the ones declared on the stack or in the global scope.

The owner of a given resource is an object or a piece of code that's responsible for the resource's release. Ownership falls into two classes—automatic and explicit. An object is owned automatically if its release is guaranteed by the mechanisms of the language. For instance, an object embedded inside another object is guaranteed to be destroyed when the outer object is destroyed. The outer object is thus considered to be the owner of the embedded object.

Similarly, every object that's declared on the stack (as an automatic variable) is guaranteed to be released (destroyed) when the flow of control leaves the scope in which the object is defined. In this case, the scope itself is considered the owner of the object. Notice that automatic ownership is compatible with all other mechanisms of the language, including exceptions. It doesn't matter how you exit a scope—normal flow of control, a break statement, a return, a goto, or a throw—automatic resources are always cleaned up.

So far, so good! The problem starts with pointers, handles, and abstract states. If access to a resource is through a pointer, as is the case with objects allocated on the heap, C++ doesn't automatically take care of its release. Instead, the programmer has to explicitly release the resource, using the appropriate programming construct. For instance, if the object in question was created by calling new, it should be deallocated by calling delete. A file that was opened using CreateFile (Win32 API) should be closed using CloseHandle. A critical section entered using EnterCriticalSection should be exited using LeaveCriticalSection, etc. A "naked" pointer, file handle, or a state of a critical section has no owner that would guarantee its eventual release. The basic premise of resource management is to make sure that every resource has its owner.

The First Rule of Acquisition

A pointer, a handle, a state of a critical section will have its owner only if we encapsulate it in objects that follow the First Rule of Acquisition: Allocate resources in constructors and release them in corresponding destructors.

Once you encapsulate all resources according to this rule, you're guaranteed not to have any resource leaks in your program. This is pretty obvious if you only consider those encapsulating objects that are allocated on the stack or are embedded inside other objects. But what about those that are allocated dynamically? Not to worry! Anything that's allocated dynamically is considered a resource, and consequently will also have to be encapsulated according to the rule above. This chain of objects encapsulating objects encapsulating resources has to end somewhere. It ends with the top-level owners, which are either automatic or static. These are guaranteed to be released on exiting the scope or the program, respectively.

Here's a classic example of resource encapsulation. In a multithreaded application, the problem of sharing an object between threads is usually solved by associating a critical section with such an object. Every client that wants to access this shared resource has to first acquire the critical section. For instance, this is how a critical section might be implemented in Win32:

class CritSect
  friend class Lock;
  CritSect () { InitializeCriticalSection (&_critSection); }
  ~CritSect () { DeleteCriticalSection (&_critSection); }
  void Acquire ()
    EnterCriticalSection (&_critSection);
  void Release ()
    LeaveCriticalSection (&_critSection);

  CRITICAL_SECTION _critSection;

The tricky part is that we have to make sure that each client entering the critical section also exits it. The "entered" state of a critical section is therefore a resource and should be encapsulated. The encapsulator is traditionally called a lock:

class Lock
  Lock (CritSect& critSect)
    : _critSect (critSect)
    _critSect.Acquire ();
  ~Lock ()
    _critSect.Release ();
  CritSect & _critSect;

Locks are used in the following manner:

void Shared::Act () throw (char *)
  Lock lock (_critSect);
  // perform action -- may throw
  // automatic destructor of lock

Notice that, no matter what happens, the critical section is guaranteed to be released by the mechanisms of the language.

There's one important thing to remember—each resource has to be encapsulated separately. That's because resource allocation is almost always a failure-prone operation, if only because there's always a finite supply of any given resource. We'll assume that a failed resource allocation might result in an exception—in fact, very often this is exactly what should happen. So if you're trying to kill two birds with one stone, or allocate two resources in one constructor, you might get into trouble. Just think what happens when the first allocation succeeds and the second one throws. Since the construction hasn't been completed, the destructor won't be called, and the first resource will leak out.

This situation can be avoided easily. Whenever you have a class that requires more than one resource, write small encapsulators for them and embed them in your class. Every fully constructed embedding is guaranteed to be deleted, even if the construction of the embedding object doesn't complete.

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.


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.


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.


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.


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


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


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.


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.


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