C++ STL map容器值为指针时怎么释放内存

// 站点与TCP连接映射表 （key为ip_port_stationCode, value为 clientSocket*）
std::map<String, DataUpload*> g_TcpConnMap;

// 遍历站点列表，为每个服务器id[ip:port]的每个站点(station code)建立一个TCP连接
for (auto& staionItem : server.Host().stationListConf)
{
 		// ip_port_stationCode 服务器地址_端口_站点编码 唯一确定一个TCP连接
 		char strTcpCode[128] = { 0 };
 		sprintf(strTcpCode, "%s_%d_%s", host.host, host.port, staionItem.sscode);
 		
 		String strTcpTemp(strTcpCode);

 		clientSocket* pclientSock=
 			new clientSocket(host.host, host.port);
 		
 		g_TcpConnMap.insert(std::make_pair(strTcpTemp, pclientSock));
}

// 释放资源
for (auto iter = g_TcpConnMap.begin(); iter != g_TcpConnMap.end(); )
{
 	auto second = iter->second;
 	if (second)
 	{
 		delete second;				  // 释放指针
 		second = NULL;
 		g_TcpConnMap.erase(iter++);	  // 从map中删除元素，注意iter++的写法
 	}
}

g_TcpConnMap.clear();

for(iter = list.begin(); iter != list.end();) {
if (shouldDelete(*iter))
	iter = list.erase(iter);
else
	++iter;
}

list.erase(std::remove_if(list.begin(), list.end(), shouldDelete), list_end());

for(iter = map.begin(); iter != map.end();) {
  if (shouldDelete(*iter))
     map.erase(iter++);
  else
     ++iter;
}