Re: Hidden Features and Dark Corners of C++/STL

ironsel2000@gmail.com (puzzlecracker) wrote (abridged):


It's hard to know which tricks are obscure enough to count. I find
declarations in if-statements useful:

     if (Object *p = get_object())
          p->use();

It's concise, and also helps minimise the scope of p, making it harder to
accidentally use it when it is undefined or NULL. It's convenient enough
that I sometimes adding bool conversions to my own classes in order to
use it:

     if (Object o = get_object())
          o.use();

The correct way to do that is itself probably a trick. Simply adding
operator bool() is a bad idea because it enables conversions to int,
which are scarily general. There is more on this here:
    http://www.artima.com/cppsource/safebool.html

std::partition can be handy if you are dealing with raw pointers (is this
dark enough?) Std::erase() will overwrite some pointers with other
pointers, which can lead to memory leaks, but with std::partition every
pointer is preserved.

     void predicate_delete( std::vector<int *> &v ) {

         std::vector<int *>::iterator i = std::partition(
                 v.begin(), v.end(), predicate() );

         for (std::vector<int *>::iterator j = i; j != v.end(); ++j) {
             // delete *j would leave an invalid value in the vector,
             // so remove it first.
             int *p = *j;
             *j = 0;
             delete p;
         }

         v.erase( i, v.end() );
     }

Not everyone knows that URLs are valid C++ syntax. Admittedly that's
largely because it's not very useful:

     int main() {
         http://www.boost.org/
         return 0;
     }

-- Dave Harris, Nottingham, UK.

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