[solved] polymorphic sorting functors
* Thomas J. Gritzan <phygon_antispam@gmx.de>:
L. Kliemann schrieb:
My function f shall implement an algorithm which at some point of its
operation has to sort things. I wish to use the algorithms with different
ways of sorting. In which way to sort shall be passed to the function by some
parameter. Wouldn't it be an elegant way to allow that parameter to resemble
the corresponding one in the std::sort function, in order that my function f
can just pass it through?
If you want to change the sorting behaviour at run-time, you could pass
a tr1::function object to std::sort.
Great! I'd never heard of tr1 before, but it seems to be a solution.
This code works (using gcc 4.2.4, produced no warnings with -Wall and
-Wextra):
#include <iostream>
#include <vector>
#include <algorithm>
#include <tr1/functional>
using namespace std;
typedef tr1::function <bool (int, int)> func_t;
class cmp_base : public std::binary_function<int, int, bool> {
public:
virtual bool operator()(int i, int j) = 0; };
class cmp_inc : public cmp_base {
public:
virtual bool operator()(int i, int j) { return i<j; } };
class cmp_dec : public cmp_base {
public:
virtual bool operator()(int i, int j) { return i>j; } };
void sort_it(vector<int> *v, func_t cmp) {
sort(v->begin(), v->end(), cmp); }
int main(void) {
vector<int> v;
v.push_back(10);v.push_back(1);v.push_back(20);
cmp_dec cmp1;
sort_it(&v, cmp1);
cout << "decreasing:" << endl;
for (unsigned int i=0; i<v.size(); ++i) { cout << v.at(i) << endl; }
cmp_inc cmp2;
sort_it(&v, cmp2);
cout << "increasing:" << endl;
for (unsigned int i=0; i<v.size(); ++i) { cout << v.at(i) << endl; }
return 0; }