[hiredis]Multiple hincrbys only return one result(REDIS_REPLY_INTEGER)

Question

When using hiredis, use redisAppendCommand to put multiple hincrby commands, the reply->type result of redisGetReply is REDIS_REPLY_INTEGER, and only one of the results is returned.
But when I use hmget, the result of reply->type is REDIS_REPLY_ARRAY.

Answer 1

Since you call redisAppendCommand multiple times, you should call redisGetReply the same number of times to get all replies. For each reply, it's of type REDIS_REPLY_INTEGER. Because the reply type of hincrby is integer type, or array type.

The reply type of hmget is array reply, and that's why you get REDIS_REPLY_ARRAY.

Since you tag the question with c++, you can try redis-plus-plus, which is a user-friendly C++ client for Redis and you don't need to parse the reply manually:

auto r = sw::redis::Redis("tcp://127.0.0.1:6379");
for (auto idx = 0; idx < 5; ++idx) {
    r.hincrby("key", "field", 1);
}
std::vector<std::string> fields = {"f1", "f2"};
std::vector<std::optinal<std::string>> vals;
r.hmget("key", fields.begin(), fields.end(), std::back_inserter(vals));

Disclaimer: I'm the author of redis-plus-plus.

Answer 2

Thank you very much for answering my question.
And the official reply from HIREDIS is here.
https://github.com/redis/hiredis/issues/1143

This is correct given the specifications of both commands.

The hmget command returns an array reply, while hincrby returns an. integer.

Here is a small example that appends several HINCRBY commands and then prints each of the replies.