std::sort in c++?

Question

I want to sort a vector using sort algorithm in C++.

str is the name of std::vector<int> I want to sort.

What's the difference between this:

std::sort(str.rend(),str.rbegin())

and this:

std::sort(str.begin(),str.end())

Answer 1

Assuming you intend to use std::sort to sort the string (since neither std::vector nor std::string have a sort method), the first statement is incorrect and leads to undefined behaviour (UB):

std::sort(str.rend(),str.rbegin());

Here, std::sort will attempt to dereference str.rend(), which is a "past the end" iterator. De-referencing such an iterator is UB.

A correct use of reverse iterators would be

std::sort(str.rbegin(),str.rend());

This would result in the string/vector being sorted in descending order.

Answer 2

The iterators in the standard library on lots of containers and other things (like std::string) have a reverse variety which begin with r (rbegin(), rend and the like). These will iterate in the reverse-sequential order. Using just begin and end will sort your string in the correct format from start to finish.

Try to avoid using the reverse iterators and just use the regular begin() and end() on your strings:

std::string str = "bacd";
std::sort( str.begin(),str.end() );
std::cout << str << std::endl; // should produce "abcd" on your output, without quotes

Edit:

So... you want vector<int> to be sorted instead? If so, do the same as above, except call std::sort with the begin() and end() of your std::vector<int>.