STL greater<T>() 和less<T>()

greater() 和less()函数经常使用在sort()中用来对容器进行升序或者降序排序，或者用在push_heap()和pop_heap()中用来构建最小堆（greater）或者最大堆(less).

二者包含在头文件functional中

原型如下：

//包含在头文件<functional>中

// TEMPLATE STRUCT greater
emplate<class _Ty>
struct greater
: public binary_function<_Ty, _Ty, bool>
{   // functor for operator>
bool operator()(const _Ty& _Left, const _Ty& _Right) const
{   // apply operator> to operands
return (_Left > _Right);
}
};

// TEMPLATE STRUCT less
emplate<class _Ty>
struct less
: public binary_function<_Ty, _Ty, bool>
{   // functor for operator<
bool operator()(const _Ty& _Left, const _Ty& _Right) const
{   // apply operator< to operands
return (_Left < _Right);
}
};

示例：

// range heap example
#include <iostream>     // std::cout
#include <algorithm>    // std::make_heap, std::pop_heap, std::push_heap, std::sort_heap
#include <vector>       // std::vector

int main () {
int myints[] = {10,20,30,5,15};
std::vector<int> v(myints,myints+5);

std::make_heap (v.begin(),v.end());
std::cout << "initial max heap   : " << v.front() << '\n';

std::pop_heap (v.begin(),v.end()); v.pop_back();
std::cout << "max heap after pop : " << v.front() << '\n';

v.push_back(99); std::push_heap (v.begin(),v.end());
std::cout << "max heap after push: " << v.front() << '\n';

std::sort_heap (v.begin(),v.end());

std::cout << "final sorted range :";
for (unsigned i=0; i<v.size(); i++)
std::cout << ' ' << v[i];

std::cout << '\n';

return 0;
}