Splitting a string by a character

I know this is a quite easy problem but I just want to solve it for myself once and for all

I would simply like to split a string into an array using a character as the split delimiter. (Much like the C#'s famous .Split() function. I can of course apply the brute-force approach but I wonder if there anything better than that.

So far the I've searched and probably the closest solution approach is the usage of strtok(), however due to it's inconvenience(converting your string to a char array etc.) I do not like using it. Is there any easier way to implement this?

Note: I wanted to emphasize this because people might ask "How come brute-force doesn't work". My brute-force solution was to create a loop, and use the substr() function inside. However since it requires the starting point and the length, it fails when I want to split a date. Because user might enter it as 7/12/2012 or 07/3/2011, where I can really tell the length before calculating the next location of '/' delimiter.

Solution 1:

Using vectors, strings and stringstream. A tad cumbersome but it does the trick.

#include <string>
#include <vector>
#include <sstream>

std::stringstream test("this_is_a_test_string");
std::string segment;
std::vector<std::string> seglist;

while(std::getline(test, segment, '_'))
{
   seglist.push_back(segment);
}

Which results in a vector with the same contents as

std::vector<std::string> seglist{ "this", "is", "a", "test", "string" };

Solution 2:

Boost has the split() you are seeking in algorithm/string.hpp:

std::string sample = "07/3/2011";
std::vector<std::string> strs;
boost::split(strs, sample, boost::is_any_of("/"));

Solution 3:

Another way (C++11/boost) for people who like RegEx. Personally I'm a big fan of RegEx for this kind of data. IMO it's far more powerful than simply splitting strings using a delimiter since you can choose to be be a lot smarter about what constitutes "valid" data if you wish.

#include <string>
#include <algorithm>    // copy
#include <iterator>     // back_inserter
#include <regex>        // regex, sregex_token_iterator
#include <vector>

int main()
{
    std::string str = "08/04/2012";
    std::vector<std::string> tokens;
    std::regex re("\\d+");

    //start/end points of tokens in str
    std::sregex_token_iterator
        begin(str.begin(), str.end(), re),
        end;

    std::copy(begin, end, std::back_inserter(tokens));
}

Solution 4:

Another possibility is to imbue a stream with a locale that uses a special ctype facet. A stream uses the ctype facet to determine what's "whitespace", which it treats as separators. With a ctype facet that classifies your separator character as whitespace, the reading can be pretty trivial. Here's one way to implement the facet:

struct field_reader: std::ctype<char> {

    field_reader(): std::ctype<char>(get_table()) {}

    static std::ctype_base::mask const* get_table() {
        static std::vector<std::ctype_base::mask> 
            rc(table_size, std::ctype_base::mask());

        // we'll assume dates are either a/b/c or a-b-c:
        rc['/'] = std::ctype_base::space;
        rc['-'] = std::ctype_base::space;
        return &rc[0];
    }
};

We use that by using imbue to tell a stream to use a locale that includes it, then read the data from that stream:

std::istringstream in("07/3/2011");
in.imbue(std::locale(std::locale(), new field_reader);

With that in place, the splitting becomes almost trivial -- just initialize a vector using a couple of istream_iterators to read the pieces from the string (that's embedded in the istringstream):

std::vector<std::string>((std::istream_iterator<std::string>(in),
                          std::istream_iterator<std::string>());

Obviously this tends toward overkill if you only use it in one place. If you use it much, however, it can go a long ways toward keeping the rest of the code quite clean.

Solution 5:

Since nobody has posted this yet: The c++20 solution is very simple using ranges. You can use a std::ranges::views::split to break up the input, and then transform the input into std::string or std::string_view elements.

#include <ranges>


...

// The input to transform
const auto str = std::string{"Hello World"};

// Function to transform a range into a std::string
// Replace this with 'std::string_view' to make it a view instead.
auto to_string = [](auto&& r) -> std::string {
    const auto data = &*r.begin();
    const auto size = static_cast<std::size_t>(std::ranges::distance(r));

    return std::string{data, size};
};

const auto range = str | 
                   std::ranges::views::split(' ') | 
                   std::ranges::views::transform(to_string);

for (auto&& token : str | range) {
    // each 'token' is the split string
}

This approach can realistically compose into just about anything, even a simple split function that returns a std::vector<std::string>:

auto split(const std::string& str, char delimiter) -> std::vector<std::string>
{
    const auto range = str | 
                       std::ranges::views::split(delimiter) | 
                       std::ranges::views::transform(to_string);

    return {std::ranges::begin(range), std::ranges::end(range)};
}

Live Example