hiredis 是redis官方推荐的C/C++客户端库，笔者的使用场景是对二进制数据进行读写，初次使用有些需要格外注意的地方，可以称为踩过的小坑吧。
笔者使用hiredis 0.13.3， 对redis的读写操作进行了简单封装，以hash结构为例，代码片断如下：

bool RedisHandler::HGet(const string &name, const string &key, string &val)
{
	for (int retry = 0; retry < MAX_RETRY_TIMES; ++ retry) {
		if (!connected && !Reconnect()) {
			continue;
		}

		redisReply *reply = (redisReply *) redisCommand(redis_context, "HGET %s %s", name.data(), key.data());
		if (NULL == reply) {
			log(LOG_ERROR, "redis connection exception: %s\n", redis_context->errstr);
			connected = false;
			continue;
		}

		if (reply->type != REDIS_REPLY_STRING) {
			if (reply->type == REDIS_REPLY_ERROR) {
				log(LOG_ERROR, "redis HGet exception: %s\n", reply->str);
			}
			freeReplyObject(reply);
			return false;
		}

		val = string(reply->str, reply->len);
		freeReplyObject(reply);
		return true;
	}

	return false;
}

bool RedisHandler::HSet(const string &name, const string &key, const string &val)
{
	for (int retry = 0; retry < MAX_RETRY_TIMES; ++ retry) {
		if (!connected && !Reconnect()) {
			continue;
		}

		redisReply *reply = (redisReply *) redisCommand(redis_context, "HSET %s %s %b", name.data(), key.data(), val.data(), val.size());
		if (NULL == reply) {
			log(LOG_ERROR, "redis connection exception: %s\n", redis_context->errstr);
			connected = false;
			continue;
		}

		if (reply->type != REDIS_REPLY_INTEGER) {
			if (reply->type == REDIS_REPLY_ERROR) {
				log(LOG_ERROR, "redis HSet exception: %s\n", reply->str);
			}
			freeReplyObject(reply);
			return false;
		}

		freeReplyObject(reply);
		return true;
	}

	return false;
}

对于二进制数据存取有如下两点需要注意：
1. 对于二进制（如thrift序列化后的数据）构造格式输入时，需使用”%b”, val.data(), val.size() 的形式；
2. 对于读取存储在redis内的二进制数据时， 对返回的string一定要通过string(reply->str, reply->len)构造返回，才能读取到完整的数据；

其实对于以上注意，hiredis官方文档也有明确说明，只是我们在写时没有注意或仔细查看了，原文如下：

When you need to pass binary safe strings in a command, the %b specifier can be used. Together with a pointer to the string, it requires a size_t length argument of the string:

reply = redisCommand(context, "SET foo %b", value, (size_t) valuelen);

Refer：
1 https://github.com/redis/hiredis
2 http://yaocoder.blog.51cto.com/2668309/1297031