Can we create std::istringstream object from a reversed std::string

Question

I am learning C++ using recommended C++ books. In particular, i read about std::istringstream and saw the following example:

std::string s("some string");
std::istringstream ss(s);
std::string word;
while(ss >> word)
{
    std::cout<<word <<" ";
}

Actual Output

some string

Desired Output

string some

My question is that how can we create the above std::istringstream object ss using the reversed string(that contains the word in the reverse order as shown in the desired output)? I looked at std::istringstream's constructors but couldn't find one that takes iterators so that i can pass str.back() and str.begin() instead of passing a std::string.

Answer 1

You can pass iterators to the istringstream constructor indirectly if you use a temporary string:

#include <sstream>
#include <iostream>

int main()
{
    std::string s{"Hello World\n"};
    std::istringstream ss({s.rbegin(),s.rend()});
    std::string word;
    while(ss >> word)
    {
        std::cout<<word <<" ";
    }
}

Output:

dlroW olleH 

Though thats reversing the string, not words. If you want to print words in reverse order a istringstream alone does not help much. You can use some container to store the extracted words and then print them in reverse:

#include <sstream>
#include <iostream>
#include <vector>

int main()
{
    std::string s{"Hello World\n"};
    std::istringstream ss(s);
    std::string word;
    std::vector<std::string> words;
    while(ss >> word)
    {
        words.push_back(word);
    }
    for (auto it = words.rbegin(); it != words.rend(); ++it) std::cout << *it << " ";
}

Output:

World Hello 

Answer 2

Since you added the c++20 tag:

#include <sstream>
#include <string>
#include <iostream>
#include <vector>
#include <ranges>


int main()
{
    std::vector<std::string> vec;
    std::string s("some string");
    std::string word;
    std::istringstream ss(s);

    while(ss >> word)
    {
        vec.push_back(word);
    }

    for (auto v : vec | std::views::reverse)
    {
        std::cout << v << ' ';
    }
}