A C++ STL String Tokenizer

• Download demo project - 5 Kb

Introduction

The class CTokenizer I am presenting in this article is capable of tokenizing an STL string when the set of character separators is specified by a predicate class. This is a very generally designed as a class template:

template <class Pred>
void CTokenizer { /*...*/ };

The separating (tokenizing) criteria being implemented in the argument predicate class Pred. The predicate classes are usually derived from unary_function<char, bool> and implement the () operator. I am giving only three examples of predicate classes: CIsSpace where the set of separators contains the white spaces 0x09-0x0D and 0x20, CIsComma where the separator is the comma character ',' and CIsFromString where the set of separators is specified by the characters in a STL string. Other predicate classes can be easily added as needed.

Implementation

First I will present the implemented predicates.

For the case when the separators are white spaces 0x09-0x0D and 0x20;

class CIsSpace : public unary_function<char, bool>
{
public:
  bool operator()(char c) const;
};

inline bool CIsSpace::operator()(char c) const
{
  // isspace<char> returns true if c is a white-space character 

  // (0x09-0x0D or 0x20)

  return isspace<char>(c);
}

For the case where the separator is the comma character ',':

class CIsComma : public unary_function<char, bool>
{
public:
  bool operator()(char c) const;
};

inline bool CIsComma::operator()(char c) const
{
  return (',' == c);
}

For the case where the separator is a character from a set of characters given in a STL string:

class CIsFromString : public unary_function<char, bool>
{
public:
  //Constructor specifying the separators

  CIsFromString::CIsFromString(string const& rostr) : m_ostr(rostr) {}
  bool operator()(char c) const;

private:
  string m_ostr;
};

inline bool CIsFromString::operator()(char c) const
{
  int iFind = m_ostr.find(c);
  if(iFind != string::npos)
    return true;
  else
    return false;
}

Finally the string tokenizer class implementing the Tokenize() function is a static member function. Notice that CIsSpace is the default predicate for the Tokenize() function.

template <class Pred=CIsSpace>
class CTokenizer
{
public:
  //The predicate should evaluate to true when applied to a separator.

  static void Tokenize(vector<string>& roResult, string const& rostr, 
                       Pred const& roPred=Pred());
};

//The predicate should evaluate to true when applied to a separator.

template <class Pred>
inline void CTokenizer<Pred>::Tokenize(vector<string>& roResult, 
                                            string const& rostr, Pred const& roPred)
{
  //First clear the results vector

  roResult.clear();
  string::const_iterator it = rostr.begin();
  string::const_iterator itTokenEnd = rostr.begin();
  while(it != rostr.end())
  {
    //Eat seperators

    while(roPred(*it))
      it++;
    //Find next token

    itTokenEnd = find_if(it, rostr.end(), roPred);
    //Append token to result

    if(it < itTokenEnd)
      roResult.push_back(string(it, itTokenEnd));
    it = itTokenEnd;
  }
}

How to use

The following code snippet is showing some simple usage examples, one for each one of the implemented predicates:

//Test CIsSpace() predicate

cout << "Test CIsSpace() predicate:" << endl;
//The Results Vector

vector<string> oResult;
//Call Tokeniker

CTokenizer<>::Tokenize(oResult, " wqd \t hgwh \t sdhw \r\n kwqo \r\n  dk ");
//Display Results

for(int i=0; i<oResult.size(); i++)
  cout << oResult[i] << endl;

//Test CIsComma() predicate

cout << "Test CIsComma() predicate:" << endl;
//The Results Vector

vector<string> oResult;
//Call Tokeniker

CTokenizer<CIsComma>::Tokenize(oResult, "wqd,hgwh,sdhw,kwqo,dk", CIsComma());
//Display Results

for(int i=0; i<oResult.size(); i++)
  cout << oResult[i] << endl;

//Test CIsFromString predicate

cout << "Test CIsFromString() predicate:" << endl;
//The Results Vector

vector<string> oResult;
//Call Tokeniker

CTokenizer<CIsFromString>::Tokenize(oResult, ":wqd,;hgwh,:,sdhw,:;kwqo;dk,", 
                                          CIsFromString(",;:"));
//Display Results

cout << "Display strings:" << endl;
for(int i=0; i<oResult.size(); i++)
  cout << oResult[i] << endl;

Conclusion

The project StringTok.zip attached to this article includes the source code of the presented CTokenizer class and some test code. I am interested in any opinions and new ideas about this implementation.