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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

9.3. Making an Initializer List Exception-Safe

Problem

You have to initialize your data members in the constructor’s initializer list, and, therefore, cannot use the approach described in Recipe 9.2.

Solution

Use a special syntax for try and catch that catches exceptions thrown in the initializer list. Example 9-3 shows how.

Example 9-3. Handling exceptions in an initializer

#include <iostream>
#include <stdexcept>

using namespace std;

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

class Broker {
  
public:
   Broker (int devno1, int devno2)
      try : dev1_(Device(devno1)),   // Create these in the initializer
            dev2_(Device(devno2)) {} // list.
      catch (...) {
         throw; // Log the message or translate the error here (see
                // the discussion)
      }
  ~Broker() {}

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

int main() {

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

Discussion

The syntax for handling exceptions in initializers looks a little different from the traditional C++ syntax because it uses the try block as the constructor body. The critical part of Example 9-3 is the Broker constructor:

Broker (int devno1, int devno2) // Constructor header is the same try : // Same idea as a try {...} block dev1_(Device(devno1)), // The initializers follow dev2_(Device(devno2)) { // This is the constructor body. } catch (...) { // The catch handler is *after* throw; // the ...
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Publisher Resources

ISBN: 0596007612Supplemental ContentErrata Page