Exception handling has costs, and we pay at least some of them even if we never use the keywords try, throw, or catch.

• If we never use any exception-handling features:

  • we pay for the space used by the data structures needed to keep track of which objects are fully constructed (MECpp item 10)
  • we pay for the time needed to keep these data structures up to date
  • Programs compiled with support for exceptions are typically slower and larger than their counterparts compiled without support for exceptions

• If we include try-catch blocks:

  • the cost varies from compiler to compiler.
  • roughly, the overall code size increases by 5-10%, assuming no exceptions are thrown
  • roughly, the overall runtime goes up by 5-10%, assuming no exceptions are thrown

• If we include exception specifications:

  • they generally incurs about the same cost as a try block

• The cost of throwing an exception:

  • Compared to a normal function return, returning from a function by throwing an exception may be as much as three orders of magnitude slower

Solution

To minimize the exception-related costs,

• compile without support for exceptions when that is feasible;
• limit the use of try blocks, and exception specifications to locations where we really need them;
• throw exceptions only under conditions that are truly exceptional;
• profile the software (MECpp item 16) to determine if exception support is the bottleneck
  • If it is, consider switching to different compilers, ones that provide more efficient implementations of C++’s exception-handling features.