這是干嗎用的那？指點指點啊？越詳細越好啊啊！！謝謝！！！！！！

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h:

#include <limits>
#include <iostream>

namespace MyLib {
   template <class T>
   class MyAlloc {
     public:
       // type definitions
       typedef T        value_type;
       typedef T*       pointer;
       typedef const T* const_pointer;
       typedef T&       reference;
       typedef const T& const_reference;
       typedef std::size_t    size_type;
       typedef std::ptrdiff_t difference_type;

       // rebind allocator to type U
       template <class U>
       struct rebind {
           typedef MyAlloc<U> other;
       };

       // return address of values
       pointer address (reference value) const {
           return &value;
       }
       const_pointer address (const_reference value) const {
           return &value;
       }

       /* constructors and destructor
        * - nothing to do because the allocator has no state
        */
       MyAlloc() throw() {
       }
       MyAlloc(const MyAlloc&) throw() {
       }
       template <class U>
         MyAlloc (const MyAlloc<U>&) throw() {
       }
       ~MyAlloc() throw() {
       }

       // return maximum number of elements that can be allocated
       size_type max_size () const throw() {
           return std::numeric_limits<std::size_t>::max() / sizeof(T);
       }

       // allocate but don't initialize num elements of type T
       pointer allocate (size_type num, const void* = 0) {
           // print message and allocate memory with global new
           std::cerr << "allocate " << num << " element(s)"
                     << " of size " << sizeof(T) << std::endl;
           pointer ret = (pointer)(::operator new(num*sizeof(T)));
           std::cerr << " allocated at: " << (void*)ret << std::endl;
           return ret;
       }

       // initialize elements of allocated storage p with value value
       void construct (pointer p, const T& value) {
           // initialize memory with placement new
           new((void*)p)T(value);
       }

       // destroy elements of initialized storage p
       void destroy (pointer p) {
           // destroy objects by calling their destructor
           p->~T();
       }

       // deallocate storage p of deleted elements
       void deallocate (pointer p, size_type num) {
           // print message and deallocate memory with global delete
           std::cerr << "deallocate " << num << " element(s)"
                     << " of size " << sizeof(T)
                     << " at: " << (void*)p << std::endl;
           ::operator delete((void*)p);
       }
   };

   // return that all specializations of this allocator are interchangeable
   template <class T1, class T2>
   bool operator== (const MyAlloc<T1>&,
                    const MyAlloc<T2>&) throw() {
       return true;
   }
   template <class T1, class T2>
   bool operator!= (const MyAlloc<T1>&,
                    const MyAlloc<T2>&) throw() {
       return false;
   }
}

cpp:
#include <vector>
#include "myalloc.hpp"

int main()
{
    // create a vector, using MyAlloc<> as allocator
    std::vector<int,MyLib::MyAlloc<int> > v;

    // insert elements
    // - causes reallocations
    v.push_back(42);
    v.push_back(56);
    v.push_back(11);
    v.push_back(22);
    v.push_back(33);
    v.push_back(44);
}

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不常見的數學咚咚：
#include <iostream>
#include <complex>
using namespace std;

int main()
{
    /* complex number with real and imaginary parts
     * - real part: 4.0
     * - imaginary part: 3.0
     */
    complex<double> c1(4.0,3.0);

    /* create complex number from polar coordinates
     * - magnitude: 5.0
     * - phase angle: 0.75
     */
    complex<float> c2(polar(5.0,0.75));

    // print complex numbers with real and imaginary parts
    cout << "c1: " << c1 << endl;
    cout << "c2: " << c2 << endl;

    // print complex numbers as polar coordinates
    cout << "c1: magnitude: " << abs(c1)
         << " (squared magnitude: " << norm(c1) << ") "
         <<    " phase angle: " << arg(c1) << endl;
    cout << "c2: magnitude: " << abs(c2)
         << " (squared magnitude: " << norm(c2) << ") "
         <<    " phase angle: " << arg(c2) << endl;

    // print complex conjugates
    cout << "c1 conjugated:  " << conj(c1) << endl;
    cout << "c2 conjugated:  " << conj(c2) << endl;

    // print result of a computation
    cout << "4.4 + c1 * 1.8: " << 4.4 + c1 * 1.8 << endl;

    /* print sum of c1 and c2:
     * - note: different types
     */
    cout << "c1 + c2:        "
         << c1 + complex<double>(c2.real(),c2.imag()) << endl;

    // add square root of c1 to c1 and print the result
    cout << "c1 += sqrt(c1): " << (c1 += sqrt(c1)) << endl;
}