C++ - Iterating over std::vector<> returned from find_if
// find_if example
#include <iostream> // std::cout
#include <algorithm> // std::find_if
#include <vector> // std::vector
bool IsOdd (int i) {
return ((i%2)==1);
}
int main () {
std::vector<int> myvector;
myvector.push_back(10);
myvector.push_back(25);
myvector.push_back(40);
myvector.push_back(55);
std::vector<int>::iterator it = std::find_if (myvector.begin(), myvector.end(), IsOdd);
std::cout << "ODD values are: " << std::endl;
while(it != myvector.end() ){
std::cout << *it << " in position " << (it - myvector.begin()) << '\n';
it = std::find_if (++it, myvector.end(), IsOdd);
}
return 0;
}
EDIT: Changed it+1
to ++it
see @David Rodríguez - dribeas comment below.
You can increment it
and use it as a starting point to iterate further:
std::cout << "odd values: ";
auto it = myvector.begin();
while(it != myvector.end())
{
it = std::find_if (it, myvector.end(), IsOdd);
if(it == myvector.end()) break;
std::cout << *it << ' ';
++it;
}
std::cout << endl;
A much more algorithm oriented approach, makes use of copy_if
, having an output vector as a result container:
std::vector<int> results;
std::copy_if(myvector.begin(), myvector.end(), std::back_inserter(results), IsOdd);
Now results contains the odd values. (Note the back:inserter is in the <iterator>
header)
You can find the index of a vector iterator (and, more generally, any random-access iterator) by subtracting the start of the sequence:
std::cout << "The index is " << (it - myvector.begin()) << '\n';
Even more generally, there is a std::distance
function which can give you the distance between forward iterators. You could use that, for example, if your container were a list
; but you probably wouldn't want to, since it would be much slower.
To find all the odd numbers, you'll need a loop to call find
again, starting from the element after the one you just found.