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Sep 6, 2012 (last update: Sep 6, 2012)

A string with the split() method

Score: 3.3/5 (198 votes)
*****

One common usage when processing text is to see it as a series of columns,
like those of a system's log, to extract one or more and use them
in different ways while discarding others. Surprisingly, C++ strings
lack a method to split themselves. The alternative (strtok()) is not really
a C++ solution, since it involves using C arrays. Another problem is its
low-level nature: the user must send a pointer to help
strtok().

In this example I have derived a class splitstring from
string. If you have a splitstring and you want to use it as a string, you
can, because it is one. But if you need to split the string, you can split
it too. The output of running method split() of a splitstring is a vector
of strings. This is more similar to high level languages where strings have
a split() method.
Possible expansions would be methods that split based on regular expressions
or constant strings.


To use as part of a larger project, the class declaration should be placed
in a separate file to be included in this and your code (but I am assuming
you already know that). The define MAIN directive should be commented out as well./p>

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// Class splitstring which adds method split()

// define MAIN if this is a standalone program
#define MAIN 1

#include <string>
#include <vector>
#include <iostream>
using namespace std;


class splitstring : public string {
    vector<string> flds;
public:
    splitstring(char *s) : string(s) { };
    vector<string>& split(char delim, int rep=0);
};

// split: receives a char delimiter; returns a vector of strings
// By default ignores repeated delimiters, unless argument rep == 1.
vector<string>& splitstring::split(char delim, int rep) {
    if (!flds.empty()) flds.clear();  // empty vector if necessary
    string work = data();
    string buf = "";
    int i = 0;
    while (i < work.length()) {
        if (work[i] != delim)
            buf += work[i];
        else if (rep == 1) {
            flds.push_back(buf);
            buf = "";
        } else if (buf.length() > 0) {
            flds.push_back(buf);
            buf = "";
        }
        i++;
    }
    if (!buf.empty())
        flds.push_back(buf);
    return flds;
}

#ifdef MAIN
main()
{
    // we define a string
    splitstring s("Humpty Dumpty sat on a wall.   Humpty Dumpty had a great fall");
    cout << s << endl;

    // splits and displays the vector of strings
    vector<string> flds = s.split(' ');
    for (int k = 0; k < flds.size(); k++)
        cout << k << " => " << flds[k] << endl;

    // now taking account of repeated delimiters
    cout << endl << "with repeated delimiters:" << endl;
    vector<string> flds2 = s.split(' ', 1);
    for (int k = 0; k < flds2.size(); k++)
        cout << k << " => " << flds2[k] << endl;

}
#endif