My take on CPLConfigOptionSetter class from GDAL cpl_conv.{cpp,h}

CPLConfigOptionSetter.cpp

// Totally untested.

class CPL_DLL CPLConfigOptionSetter
{
  public:
    CPLConfigOptionSetter(const std::string& pszKey, const std::string& osValue,
                          bool bSetOnlyIfUndefined) :
        m_osKey(osKey),
        m_osOldValue(CPLGetConfigOption(osKey.c_str(), NULL)),
        m_bRestoreOldValue(false)
    {
        if( (bSetOnlyIfUndefined &&
             CPLGetConfigOption(osKey.c_str(), NULL) == NULL) ||
            !bSetOnlyIfUndefined )
        {
            m_bRestoreOldValue = true;
            CPLSetThreadLocalConfigOption(osKey.c_str(), osValue.c_str());
        }
    }
    ~CPLConfigOptionSetter()
    {
        if( !m_bRestoreOldValue ) return;

        CPLSetThreadLocalConfigOption(m_osKey.c_str(), m_osOldValue.c_str());
    }

  private:
    const std::string m_osKey;
    const std::string m_osOldValue;
    bool m_bRestoreOldValue;

#if HAVE_CXX11
    CPLConfigOptionSetter(const CPLConfigOptionSetter&) = delete;
    CPLConfigOptionSetter& operator=(const CPLConfigOptionSetter&) = delete;
#else
    CPLConfigOptionSetter(const CPLConfigOptionSetter&);
    CPLConfigOptionSetter& operator=(const CPLConfigOptionSetter&);
#endif
};