Re: What am I missing? (template magic gone wrong)

Carl Barron <>
Thu, 28 Feb 2008 12:22:08 CST
In article <>,
Sebastian Redl <> wrote:

template <typename K, typename V, typename Allocator = std::allocator
 [, futher, implementation-defined parameters with defaults]>
class map;

   Wrong. the standard no longer allows implementation defined
parameters to the template declaration. this was an early fix to the
standard. therefore you can handle containers if you have a 21th
century compiler.

    It is simpler to have one functor class/struct and overloaded
templated operator ()'s.

struct MemberDeleter
    template <class T>
    void operator () (T &x) { delete x;}
    template <class T1,class T2>
    void operator () (std::pair<T1,T2> &x)
    { delete x.second;}

is an example

beware the that the container contains invalid ptrs after the for_each
operation , safer is to transform the contents so the ptrs are now null
ptrs (== 0) ,but not sure if it is really needed.

Easier to maintain is to store smart ptrs in containers then you won't
be bit by
    std::remove or remove_if overwritting the ptrs as it would do in most
implementations of remove[if] and sequence mutatining algorithms.

struct ptr_points_to
    int a;
    ptr_points_to(int x):a(a){}
    bool operator () (int *x) const
       return *x == a;

std::vector<int *> ptrs;
for(int i=0;i!=10;++i)
    ptrs.push_back(new int(i % 3));
std::vector<int>::iterator it = std::remove_if
now some of the ptrs are dangling , since the entries
of [ptrs.begin(), it ) are overwritten!!! in remove_if.

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