How can I split a string by a delimiter into an array?

Question

I am new to programming. I have been trying to write a function in C++ that explodes the contents of a string into a string array at a given parameter, example:

string str = "___this_ is__ th_e str__ing we__ will use__";

should return string array:

cout << stringArray[0]; // 'this'
cout << stringArray[1]; // ' is'
cout << stringArray[2]; // ' th'
cout << stringArray[3]; // 'e str'
cout << stringArray[4]; // 'ing we'
cout << stringArray[5]; // ' will use'

I can tokenize the string just fine, but the hardest part for me is how can i specify the number of elements in stringArray before assigning it the current string toke and also how to return stringArray from the function.

Would someone show me how to write the function?

Edit1: I don't necessarily need the results to been in string array just any container that i can call as a regular variable with some sort of indexing.

Answer 1

Here's my first attempt at this using vectors and strings:

vector<string> explode(const string& str, const char& ch) {
    string next;
    vector<string> result;

    // For each character in the string
    for (string::const_iterator it = str.begin(); it != str.end(); it++) {
        // If we've hit the terminal character
        if (*it == ch) {
            // If we have some characters accumulated
            if (!next.empty()) {
                // Add them to the result vector
                result.push_back(next);
                next.clear();
            }
        } else {
            // Accumulate the next character into the sequence
            next += *it;
        }
    }
    if (!next.empty())
         result.push_back(next);
    return result;
}

Hopefully this gives you some sort of idea of how to go about this. On your example string it returns the correct results with this test code:

int main (int, char const **) {
    std::string blah = "___this_ is__ th_e str__ing we__ will use__";
    std::vector<std::string> result = explode(blah, '_');

    for (size_t i = 0; i < result.size(); i++) {
        cout << "\"" << result[i] << "\"" << endl;
    }
    return 0;
}

Answer 2

Using STL (sorry no compiler not tested)

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

int main()
{
    std::vector<std::string>   result;

    std::string str = "___this_ is__ th_e str__ing we__ will use__";

    std::stringstream  data(str);

    std::string line;
    while(std::getline(data,line,'_'))
    {
        result.push_back(line); // Note: You may get a couple of blank lines
                                // When multiple underscores are beside each other.
    }
}

// or define a token

#include <vector>
#include <string>
#include <iterator>
#include <algorithm>
#include <sstream>

struct Token: public std::string  // Yes I know this is nasty.
{                                 // But it is just to demosntrate the principle.    
};

std::istream& operator>>(std::istream& s,Token& t)
{
    std::getline(s,t,'_');
   
    // *** 
    // Remove extra '_' characters from the stream.
    char c;
    while(s && ((c = s.get()) != '_')) {/*Do Nothing*/}
    if (s)
    {
        s.unget(); // Put back the last char as it is not '_'
    }
    return s;
}

int main()
{   

    std::string str = "___this_ is__ th_e str__ing we__ will use__";

    std::stringstream  data(str);

    std::vector<std::string>   result(std::istream_iterator<Token>(data),
                                      std::istream_iterator<Token>());
}