I'd like to save myself some typing and therefore define something like this:
using namespace std;
vector<MyClass> vec;
auto vecsort = bind(sort, vec.begin(), vec.end(), [] (MyClass const &a, MyClass const &b) {
// custom comparison function
});
vecsort(); // I want to use vecsort() a lot afterwards
For some reason this doesn't compile - why?
Using boost is not an option.
Minimal working example:
#include <vector>
#include <utility>
#include <algorithm>
#include <functional>
using namespace std;
int main() {
vector<pair<int, int>> vec;
for (int i = 0; i < 10; i++)
vec.push_back(make_pair(10 - i, 0));
auto vecsort = bind(sort, vec.begin(), vec.end(), [] (pair<int, int> const &a, pair<int, int> const &b) {
return a.first < b.first;
});
vecsort();
}
Error:
error: no matching function for call to 'bind(<unresolved overloaded function type>, std::vector<std::pair<int, int> >::iterator, std::vector<std::pair<int, int> >::iterator, main()::__lambda0)'
What is Sort Function in C++? Sort is an in-built function in a C++ STL ( Standard Template Library). This function is used to sort the elements in the range in ascending or descending order.
std::sort() is a built-in function in C++'s Standard Template Library. The function takes in a beginning iterator, an ending iterator, and (by default) sorts the iterable in ascending order. The function can also be used for custom sorting by passing in a comparator function that returns a boolean.
The SORT function sorts the contents of a range or array. In this example, we're sorting by Region, Sales Rep, and Product individually with =SORT(A2:A17), copied across cells F2, H2, and J2.
Sorting a vector in C++ can be done by using std::sort(). It is defined in<algorithm> header. To get a stable sort std::stable_sort is used. It is exactly like sort() but maintains the relative order of equal elements.
The problem is that std::sort
isn't a function object. It is a function template. The easiest way to deal with the issue is to create a simple wrapper object:
struct sorter {
template <typename RndIt, typename Cmp>
void operator()(RndIt begin, RndIt end, Cmp cmp) {
std::sort(begin, end, cmp);
}
};
Now you can use
std::bind(sorter(), vec.begin(), vec.end(), [](...){ ... });
Others have mentioned why it doesn't compile, but does this alternate solution work for you? This uses another lambda, instead of bind, to create the std::function.
#include <vector>
#include <utility>
#include <algorithm>
#include <functional>
#include <iostream>
using namespace std;
int main() {
vector<pair<int, int>> vec;
for (int i = 0; i < 10; i++) {
vec.push_back(make_pair(10 - i, 0));
}
auto vecsort = [&vec] {
sort(vec.begin(), vec.end(),
[] (pair<int, int> const &a, pair<int, int> const &b) {
return a.first < b.first;
});
};
// vecsort will work as long as vec is in scope.
// vecsort will modify the original vector.
vecsort();
for (auto i : vec) {
std::cout << '(' << i.first << ", " << i.second << ") ";
}
std::cout << endl;
vec.push_back(make_pair(-42, 0));
vecsort();
for (auto i : vec) {
std::cout << '(' << i.first << ", " << i.second << ") ";
}
std::cout << endl;
}
Output:
(1, 0) (2, 0) (3, 0) (4, 0) (5, 0) (6, 0) (7, 0) (8, 0) (9, 0) (10, 0)
(-42, 0) (1, 0) (2, 0) (3, 0) (4, 0) (5, 0) (6, 0) (7, 0) (8, 0) (9, 0) (10, 0)
See it run here: http://ideone.com/W2YQKW
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With