这是干吗用的那？指点指点啊？越详细越好啊啊！！谢谢！！！！！！
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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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不常见的数学咚咚：
#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;
}