C++ stringutils

#include <iostream>
#include <sstream>
 
using std::string;
using std::stringstream;
 
class StringUtils
{
public:
    static string replace(const string& subject, const string& search, const string& replace)
    {
        string str = subject;
        size_t pos = 0;
        while((pos = str.find(search, pos)) != string::npos)
        {
             str.replace(pos, search.length(), replace);
             pos += replace.length();
        }
        return str;
    };
    //----------------------------------------------------------------------
    static int string_to_int( const string &s )
    {
        int i;
        stringstream ss;
        ss << s;
        ss >> i;
        return i;
    };
    //----------------------------------------------------------------------
    static string int_to_string( int i )
    {
        stringstream ss;
        ss << i;
        return ss.str();
    };
    //----------------------------------------------------------------------
    static bool is_numeric_string( const string &str )
    {
        if (!str.empty())
        {
            for (int i=0,ix=str.length(); i<ix; i++)
            {
                if (str[i] < '0' || '9' < str[i])
                {
                    return false;
                }
            }
            return true;
        }
        return false;
    };
    //----------------------------------------------------------------------
    static string uppercase(const std::string& str)
    {
        string s = str;
        for(size_t i=0, ix=s.length()-1; i<=ix; i++)
        {
            if ('a'<=s[i] && s[i]<='z')
            {
                s[i]-=32;
            }
        }
        return s;
    };
    //----------------------------------------------------------------------
    static string lowercase(const std::string& str)
    {
        string s = str;
        for(size_t i=0, ix=s.length()-1; i<=ix; i++)
        {
            if ('A'<=s[i] && s[i]<='Z')
            {
                s[i]+=32;
            }
        }
        return s;
    };
    //----------------------------------------------------------------------
    static string ltrim(const string& str)
    {
        size_t startpos = str.find_first_not_of(" \t\n\r");
        return string::npos != startpos ? str.substr( startpos ) : str;
    };
    //----------------------------------------------------------------------
    static string rtrim(const string& str)
    {
        size_t endpos = str.find_last_not_of(" \t\n\r");
        return string::npos != endpos ? str.substr( 0, endpos+1 ) : str;
    };
    //----------------------------------------------------------------------
    static string trim(const string& str)
    {
        string s = str;
        s.erase(s.find_last_not_of(" \t\n\r") + 1);
        s.erase(0, s.find_first_not_of(" \t\n\r"));
        return s;
    };
    //----------------------------------------------------------------------
    static bool beginswith(const string& subject, const string& search)
    {
        return subject.substr(0,search.length())==search;
    };
    //----------------------------------------------------------------------
    static bool endswith(const string& subject, const string& search)
    {
        return subject.substr(subject.length() - search.length(),search.length())==search;
    };
    //----------------------------------------------------------------------
    static bool contains(const string& subject, const string& search)
    {
        return subject.find(search)!=string::npos;
    };
    //----------------------------------------------------------------------
private:
    StringUtils(){};//static class
 
};
 
using std::cout;
using std::endl;
 
int main(int argc, char *argv[])
{
    cout << "|" << StringUtils::ltrim("   ABC   ") << "|" << endl;
    cout << "|" << StringUtils::rtrim("   ABC   ") << "|" << endl;
    cout << "|" << StringUtils::trim("   ABC   ") << "|" << endl;
    cout << "|" << StringUtils::trim("ABC") << "|" << endl;
    cout <<  StringUtils::uppercase("ABCdef") << endl;
    cout <<  StringUtils::lowercase("ABCdef") << endl;
    cout <<  StringUtils::replace("ABCDEF", "CD", "ZZ") << endl;
    cout <<  "10 is numeric? " << (StringUtils::is_numeric_string("10")? "Y" : "N") << endl;   
    cout <<  (StringUtils::beginswith("alpha", "al" )? "Y" : "N") << endl;
    cout <<  (StringUtils::endswith("alpha", "ha")? "Y" : "N") << endl;
    cout <<  (StringUtils::contains("alpha", "ha")? "Y" : "N") << endl;
 
    return 0;
}