tokenizing a string of data into a vector of structs?

问题

So I have the following string of data, which is being received through a TCP winsock connection, and would like to do an advanced tokenization, into a vector of structs, where each struct represents one record.

std::string buf = "44:william:adama:commander:stuff\n33:luara:roslin:president:data\n"

struct table_t
{
    std::string key;
    std::string first;
    std::string last;
    std::string rank;
    std::additional;
};

Each record in the string is delimited by a carriage return. My attempt at splitting up the records, but not yet splitting up the fields:

    void tokenize(std::string& str, std::vector< string >records)
{
    // Skip delimiters at beginning.
    std::string::size_type lastPos = str.find_first_not_of("\n", 0);
    // Find first "non-delimiter".
    std::string::size_type pos     = str.find_first_of("\n", lastPos);
    while (std::string::npos != pos || std::string::npos != lastPos)
    {
        // Found a token, add it to the vector.
        records.push_back(str.substr(lastPos, pos - lastPos));
        // Skip delimiters.  Note the "not_of"
        lastPos = str.find_first_not_of("\n", pos);
        // Find next "non-delimiter"
        pos = str.find_first_of("\n", lastPos);
    }
}

It seems totally unnecessary to repeat all of that code again to further tokenize each record via the colon (internal field separator) into the struct and push each struct into a vector. I'm sure there is a better way of doing this, or perhaps the design is in itself wrong.

Thank you for any help.

回答1:

For breaking the string up into records, I'd use istringstream, if only because that will simplify the changes later when I want to read from a file. For tokenizing, the most obvious solution is boost::regex, so:

std::vector<table_t> parse( std::istream& input )
{
    std::vector<table_t> retval;
    std::string line;
    while ( std::getline( input, line ) ) {
        static boost::regex const pattern(
            "\([^:]*\):\([^:]*\):\([^:]*\):\([^:]*\):\([^:]*\)" );
        boost::smatch matched;
        if ( !regex_match( line, matched, pattern ) ) {
            //  Error handling...
        } else {
            retval.push_back(
                table_t( matched[1], matched[2], matched[3],
                         matched[4], matched[5] ) );
        }
    }
    return retval;
}

(I've assumed the logical constructor for table_t. Also: there's a very long tradition in C that names ending in _t are typedef's, so you're probably better off finding some other convention.)

回答2:

My solution:

struct colon_separated_only: std::ctype<char> 
{
    colon_separated_only(): std::ctype<char>(get_table()) {}

    static std::ctype_base::mask const* get_table()
    {
        typedef std::ctype<char> cctype;
        static const cctype::mask *const_rc= cctype::classic_table();

        static cctype::mask rc[cctype::table_size];
        std::memcpy(rc, const_rc, cctype::table_size * sizeof(cctype::mask));

        rc[':'] = std::ctype_base::space; 
        return &rc[0];
    }
};

struct table_t
{
    std::string key;
    std::string first;
    std::string last;
    std::string rank;
    std::string additional;
};

int main() {
        std::string buf = "44:william:adama:commander:stuff\n33:luara:roslin:president:data\n";
        stringstream s(buf);
        s.imbue(std::locale(std::locale(), new colon_separated_only()));
        table_t t;
        std::vector<table_t> data;
        while ( s >> t.key >> t.first >> t.last >> t.rank >> t.additional )
        {
           data.push_back(t);
        }
        for(size_t i = 0 ; i < data.size() ; ++i )
        {
           cout << data[i].key <<" ";
           cout << data[i].first <<" "<<data[i].last <<" ";
           cout << data[i].rank <<" "<< data[i].additional << endl;
        }
        return 0;
}

Output:

44 william adama commander stuff
33 luara roslin president data

Online Demo : http://ideone.com/JwZuk

---

The technique I used here is described in my another solution to different question:

Elegant ways to count the frequency of words in a file

来源：https://stackoverflow.com/questions/5462022/tokenizing-a-string-of-data-into-a-vector-of-structs