Skip to Main Content
C++ Cookbook
book

C++ Cookbook

by D. Ryan Stephens, Christopher Diggins, Jonathan Turkanis, Jeff Cogswell
November 2005
Beginner to intermediate content levelBeginner to intermediate
594 pages
16h 23m
English
O'Reilly Media, Inc.
Content preview from C++ Cookbook

9.2. Making a Constructor Exception-Safe

Problem

Your constructor needs to uphold basic and strong exception-safety guarantees. See the discussion that follows for the definitions of “basic” and “strong” guarantees.

Solution

Use try and catch in the constructor to clean up properly if an exception is thrown during construction. Example 9-2 presents examples of the simple Device and Broker classes. Broker constructs two Device objects on the heap, but needs to be able to properly clean them up if an exception is thrown during construction.

Example 9-2. An exception-safe constructor

#include <iostream>
#include <stdexcept>

using namespace std;

class Device {
public:
   Device(int devno) {
      if (devno == 2)
         throw runtime_error("Big problem");
   }
  ~Device() {}
};

class Broker {
  
public:
   Broker (int devno1, int devno2) :
      dev1_(NULL), dev2_(NULL) {
      try {                            
         dev1_ = new Device(devno1);  // Enclose the creation of heap
         dev2_ = new Device(devno2);  // objects in a try block...
      }
      catch (...) {
         delete dev1_;                // ...clean up and rethrow if
         throw;                       // something goes wrong.
      }
   }
  ~Broker() {
      delete dev1_;
      delete dev2_;
   }

private:
   Broker();
   Device* dev1_;
   Device* dev2_;
};

int main() {

   try {
      Broker b(1, 2);
   }
   catch(exception& e) {
      cerr << "Exception: " << e.what() << endl;
   }
}

Discussion

To say that a constructor, member function, destructor, or anything else is “exception-safe” is to guarantee that it won’t leak resources and possibly that it won’t leave its object in an inconsistent state. In C++, these two kinds ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

C++ System Programming Cookbook

C++ System Programming Cookbook

Onorato Vaticone

Publisher Resources

ISBN: 0596007612Supplemental ContentErrata Page