3 ms·

For exceptions: - A bit unpredictable (hard to optimize) - Introduce a lot of exit points which are hard to find - They deviate from the "pay what you use,"

by spoiler 11y ago

For exceptions: - A bit unpredictable (hard to optimize) - Introduce a lot of exit points which are hard to find - They deviate from the "pay what you use," since they generate some extra code - They can introduce some nasty performance penalties (I experienced this myself a few yeas back, the compilers might be smarter these days, maybe) About the stdlib: There's a "myth" that often times the stdlib/stl is slow and doesn't do what you expect (unless you've thoroughly read the documentation, which everyone should do anyway). I can't say I was personally affected by this since I also use C++ for nothing too serious. I said "myth" because the argument against the slowness it that this is an outdated notion.

exDM69 11y ago
Most C++ compilers these days should have zero cost exception handling, meaning that the non-exceptional path should be free. This works by making the compiler add exception handler data to the executable file, ie. telling where the catch() blocks are. When an exception is thrown, the stack trace is analyzed and the appropriate catch handler is found by searching for the return addresses in the exception handler data. This can make C++ with exceptions faster than C with error checks because there's no branches to check for every error condition. Using __builtin_expect for marking the error conditions as unlikely may mitigate this issue.
- jbb555 11y ago
  The cost is that you have to ensure that all your code is exception safe unless you are extremely careful to ensure that exceptions are only thrown in places you've expected and coded for. Exception safe code is both difficult to write correctly and often has a significant run time cost.
  - exDM69 11y ago
    Agreed on both accounts but the grandparent comment was talking about runtime performance penalty, which is gone (for the non-exceptional path) in modern implementations. But yes: exception safety, even basic safety (don't leak resources or crash) is difficult, let alone strong exception safety (no side effects if exception occurs).

by spoiler 11y ago

exDM69 11y ago

Most C++ compilers these days should have zero cost exception handling, meaning that the non-exceptional path should be free. This works by making the compiler add exception handler data to the executable file, ie. telling where the catch() blocks are. When an exception is thrown, the stack trace is analyzed and the appropriate catch handler is found by searching for the return addresses in the exception handler data. This can make C++ with exceptions faster than C with error checks because there's no branches to check for every error condition. Using __builtin_expect for marking the error conditions as unlikely may mitigate this issue.

jbb555 11y ago
The cost is that you have to ensure that all your code is exception safe unless you are extremely careful to ensure that exceptions are only thrown in places you've expected and coded for. Exception safe code is both difficult to write correctly and often has a significant run time cost.
- exDM69 11y ago
  Agreed on both accounts but the grandparent comment was talking about runtime performance penalty, which is gone (for the non-exceptional path) in modern implementations. But yes: exception safety, even basic safety (don't leak resources or crash) is difficult, let alone strong exception safety (no side effects if exception occurs).