Home > Articles > Programming > C/C++

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

Like this article? We recommend

Exception Handling

Exceptions happen all the time; for example, if you attempt to open a nonexistent file or you try to connect to a remote database engine when the intervening network is down. Given the increasingly distributed nature of computing, it’s essential to handle exceptions gracefully. As we’ll see, adding exception handling to your function calls can help make code far more resilient. It’s pretty easy to do, and the users of your function calls will thank you for it!

Exceptions: try-throw-catch

Listing 10 illustrates the basic exception handler structure.

Listing 10 Generic C++ Exception Handler

   Some statements
   Some code with a throw statement

   More statements
catch (Exception_Type_Name e)
   Statements performed if an instance of the specified exception is thrown

Let’s take a look at a concrete example of an exception. To make it interesting, let’s throw an object of a class in Listing 11!

Listing 11 An Exception Handler—Throwing an Object of a Class

class AnExceptionalClass {
   explicit AnExceptionalClass();
   explicit AnExceptionalClass(int someErrorCount);
   const int getErrorCount();
   ~AnExceptionalClass() { };
   int ErrorCount;

int main() {
   try {
      // Lots of code here
      throw AnExceptionalClass(500);
      // Lots more code here
   catch(AnExceptionalClass e) {
      cout << "Exceptional value is " << e.getErrorCount() << endl;

AnExceptionalClass::AnExceptionalClass(int someErrorCount) : ErrorCount(someErrorCount)

int AnExceptionalClass::getErrorCount()
   return ErrorCount;

In relation to the preceding code, you rarely catch exceptions by value. The recommended approach is to catch them by reference for the following good reasons:

  • Polymorphism
  • Efficiency
  • Avoiding slicing

Allowing the handler to modify the exception object this might be necessary if the handler rethrows the exception.

The try block throws the exception in the form of an instance of the class AnExceptionalClass. Clearly, the exception thrown in Listing 11 is overkill! But it illustrates the idea of how an exception can occur in the middle of a block of code. The exception handler in the catch clause calls into a member function of the thrown class called getErrorCount().

Bear in mind that an uncaught exception will result in abnormal program termination. Let’s now take a look at a memory allocation exception handler in Listing 12.

Listing 12 C++ Memory Allocation Exception Handler

#define ARRAY_LIMIT 10000

struct aBigNode
   int data[100];
   aBigNode *link;
typedef aBigNode* ABigNodePtr;

aBigNode* aBigNodePtrArray[ARRAY_LIMIT];

for (int i = 0; i < ARRAY_LIMIT; i++)
aBigNodePtrArray[i] = new aBigNode;

cout << "No exceptions here\n";
catch (std::bad_alloc &)
   cout << "Ran out of memory\n";

for (int i = 0; i < ARRAY_LIMIT; i++)
delete aBigNodePtrArray[i];

Listing 12 shows a structure called aBigNode that we allocate dynamically into an array called aBigNodePtrArray. We do this until we run out of memory, at which point a bad_alloc exception is thrown. It’s that simple! Let’s now take a look at how you can write functions to throw exceptions.

Functions that Throw Exceptions and Callers that Catch Them

Listing 13 adds a function declaration just before main().

Listing 13 A Function that Throws an Exception

void aFunction(void) throw (AnExceptionalClass);

void main()

Notice from Listing 13 that the declaration of aFunction() includes the exception that the routine throws – in this case (AnExceptionalClass). Listing 14 illustrates the definition of the function from Listing 13, which also lists the exception.

Listing 14 An Exception-Throwing Function Definition

void aFunction(void) throw (AnExceptionalClass)
   //Code goes here
   //An exception condition occurs with error value CRITICAL_ERROR
   throw (AnExceptionalClass(CRITICAL_ERROR));

In Listing 14, the code encounters an error indicated by CRITICAL_ERROR. This error is pushed into the constructor of the exception class. Let’s put it all together in main() and call this new function in Listing 15 and see what happens.

Listing 15 Two Exception Handling Code Segments—One After the Other

void main()
   catch (AnExceptionalClass e)
      cout << "Exceptional value is " << e.getErrorCount() << endl;

   for (int i = 0; i < ARRAY_LIMIT; i++)
   aBigNodePtrArray[i] = new aBigNode;

   cout << "No exceptions here\n";
   catch (bad_alloc)
      cout << "Ran out of memory\n";

The first thing that happens is a call to aFunction(), which results in an exception being thrown from within aFunction(). This exception is not caught by aFunction(). Instead, the exception is caught in the first catch block in main(). We caught the exception and avoided an abnormal termination. The code then executes the next try block. In other words, our code is weaving its way carefully through the choppy waters of exception handling and normal application flow. We’re taking account of code that can throw exceptions and we’re allowing for any such eventualities.

So, you can see that exception handling isn’t difficult and helps make code stronger by avoiding abnormal terminations. If an exceptional event occurs, such as running out of memory, you can at least detect the problem and exit gracefully. This is always preferable to an abnormal termination, which often leaves a poor impression on users and leaves programmers scratching their heads when attempting a fix! If you think you should use exception handlers in your code, you’re right!

  • + 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.


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