Re: Splitting Strings in a map<string, string>

James Kanze <>
Tue, 15 Apr 2008 05:53:56 -0700 (PDT)
On Apr 15, 3:15 am, wrote:

Hey guys, I'm new to cpp. Trying to split a string (on whitespace)
into a map<string, string> and return map<string, string> from within
a function. I've cobbled this together from examples on the web and
experimenting myself:

map<string, string> get_areas_groups()
    const char* file_name = "areas_groups.txt";

    // area_group should be a string that looks like this: xxx xx
    // Three chars a space followed by two chars.
    string area_group;

    // ag is a mapping of xxx to xx
    map<string, string> ag;

I would strongly recommend a typedef here:

    typedef std::map< std::string, std::string >
                        Map ;
    Map area_groups ;

    ifstream fin (file_name);
    while (!fin.eof())

This line is definitely wrong. What you want is

    while ( std::getline( fin, area_group ) ) {

        getline(fin, area_group);

And no getline here, of course.

        string buf;
        stringstream ss(area_group);
        while (ss >> buf)

Why not:

    std::string key ;
    std::string value ;
    if ( ss >> key >> value >> std::ws && ss.get() == EOF ) {
        area_group[ key ] = value ;
    } else {
        // syntax error in the line...


More likely, you want to detect duplicate keys. In that case,
inside the if:

    if ( ! area_group.insert( Map::value_type( key, value )
            .second ) {
        // duplicate entry ...

At any rate, if you want exactly two entries, a loop is not the

          cout << buf << endl;
          // Here's where I can't figure things out.
          // The split works OK, but not in a way conducive
          // for a map insert as buf is replaced. A vector<string>
          // works great here.
          ag.insert(pair<string, string>("xxx", "xx"));
    cout << ag.size() << endl;
    return ag;

James Kanze (GABI Software)
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