c – 为什么这个函数重载不起作用？

class CConfFile
{
    public:
        CConfFile(const std::string &FileName);
        ~CConfFile();
        ...
        std::string GetString(const std::string &Section,const std::string &Key);
        void GetString(const std::string &Section,const std::string &Key,char *Buffer,unsigned int BufferSize);
        ...
}

string CConfFile::GetString(const string &Section,const string &Key)
{
    return GetKeyValue(Section,Key);
}

void GetString(const string &Section,const string &Key,unsigned int BufferSize)
{
    string Str = GetString(Section,Key);     // *** ERROR ***
    strncpy(Buffer,Str.c_str(),Str.size());
}

为什么在第二个函数中得到的函数’void GetString(const std :: string&,const std :: string&,char *,unsigned int)’的参数错误太少？

谢谢