TabをSpaceに展開

#include <string>
std::string tabToSpace(int tabSize, const std::string& s)
{
    std::string result;
    int         spacingSize = tabSize;
    for(std::string::const_iterator i = s.begin(); i != s.end(); ++i)
    {
        if(*i == '\t')
        {
            result += std::string(spacingSize, ' ');
            spacingSize = tabSize;
        }
        else
        {
            result += *i;
            --spacingSize;
            if(spacingSize == 0)
            {
                spacingSize = tabSize;
            }
        }
    }
    return result;
}