C++: delete vs. free and performance

Question

1. Consider:

   char *p=NULL;
   free(p) // or
   delete p;
   

   What will happen if I use free and delete on p?

Answer 1

Good answers all.

On the performance issue, this provides a method that most can't imagine will work, but a few know it does, surprisingly well.

The 90/10 rule is true. In my experience, there usually are multiple trouble spots, and they usually are at mid-levels of the call stack. They often are caused by using over-general data structures, but you should never fix something unless you've proven that it actually is a problem. Performance problems are amazingly unpredictable.

Fixing any single performance problem may not give you the speedup you need, but each one you fix makes the remaining ones take a larger percentage of the remaining time, so they become easier to find. The speedups combine in a compounded fashion, so you may be surprised at the final result.

When you can no longer find significant problems that you can fix, you've done about as well as you can. Sometimes, at that point, a redesign (such as using code generation) can set off a further round of speedups.