how print nth split of string with boost c++?

Question

I need to get the 2nd split of a string, in the case below "two".

I tried running this code:

#include <boost/algorithm/string.hpp>
#include <iostream>
#include <list>
#include <string>

int main()
{
    std::string s = "one,two,three,four";
    std::list<std::string> results;

    boost::split(results, s, boost::is_any_of(","));

    std::cout << results[1] << "";
}

I get this error:

error: no match for 'operator[]'

How can I solve it?

I know how split but I dont know how get the nth part in this case get "two" — newquest, Jul 18 '18 at 15:53
doesn't the `cout` line work? what does it print? by the way, prefer `std::vector` over `std::list`. `std::list` is a linked-list which is typically slower than `std::vector` and doesn't have a benefit here. — asu, Jul 18 '18 at 15:54

asu · Answer 1 · 2018-07-18T15:57:40.553

0

cout << results[1] << "";

This doesn't work because results is a std::list. std::list does not provide the [] operator. In your usecase, you should use a std::vector instead.

edited Jul 18 '18 at 15:57

answered Jul 18 '18 at 15:56

asu

1,875
17
27

but how I could do this with list and boost exist any way? – newquest Jul 18 '18 at 15:57
why would you use `std::list` rather than `std::vector`? – asu Jul 18 '18 at 15:58
Im new in c++ I know boost because use this , i dont know vector – newquest Jul 18 '18 at 15:59
It will work with `std::vector` too... you do not need `std::list` here. – asu Jul 18 '18 at 15:59

PaulMcKenzie · Accepted Answer · 2018-07-18T17:27:19.423

The other answers given shows the reason for the error in that you are using a std::list, which in turn does not provide an operator []. The easiest thing is to just use std::vector.

However, if you really wanted to use a std::list, the way you get to a certain position in the list is to advance to that position. Thus there is a std::advance function that does this, in addition to std::next, which is merely a wrapper for std::advance.

So here is a solution using std::list and std::advance.

#include <boost/algorithm/string.hpp>
#include <iostream>
#include <list>
#include <string>
#include <iterator>

int main()
{
    std::string s = "one,two,three,four";
    std::list<std::string> results;

    boost::split(results, s, boost::is_any_of(","));
    auto iter = results.begin();
    std::advance(iter, 1);
    std::cout << *iter << "";
}

Live Example

Now using std::next:

#include <boost/algorithm/string.hpp>
#include <iostream>
#include <list>
#include <string>
#include <iterator>

int main()
{
    std::string s = "one,two,three,four";
    std::list<std::string> results;

    boost::split(results, s, boost::is_any_of(","));
    auto iter = std::next(results.begin(), 1);
    std::cout << *iter << "";
}

Live Example

how print nth split of string with boost c++?

2 Answers2