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
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