stl遍历map

MapInfo* CGameConfig::getMapInfoById( int nId )
{
for (map<int, MapInfo>::iterator it = m_mapMapInfo.begin(); it != m_mapMapInfo.end(); it++)
{
if (nId == it->first)
{
return &(it->second);
}
}
CCLog("error: CGameConfig::getMapInfoById");
return NULL;
}