我可以将 MGET 与hiredis 一起使用吗？

Question

考虑以下示例：

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <hiredis/hiredis.h>

int main(int argc, char **argv) {
  redisContext *redis;
  redisReply *reply;

  redis = redisConnect("127.0.0.1", 6379);
  if(redis->err) {
    fprintf(stderr, "Connection error: %s\n", redis->errstr);
    exit(EXIT_FAILURE);
  }

  reply = redisCommand(redis, "SET %s %s", "foo", "bar");
  printf("SET %s %s: %s\n", "foo", "bar", reply->str);
  freeReplyObject(reply);

  reply = redisCommand(redis, "SET %s %s", "name", "value");
  printf("SET %s %s: %s\n", "name", "value", reply->str);
  freeReplyObject(reply);

  reply = redisCommand(redis, "MGET %s %s", "foo", "name");
  printf("MGET %s %s: %s\n", "foo", "name", reply->str);
  freeReplyObject(reply);

  exit(EXIT_SUCCESS);
}

输出是：

PING: PONG
SET foo bar: OK
GET foo: bar
SET name value: OK
MGET foo name: (null)

这是关于从MGET返回的。我可以使用hiredis获取多键吗？

Answer 1

一个 redisReply 是一个类型化的对象（见 type 字段），一个多批量回复有一个特定的类型（REDIS_REPLY_ARRAY）。 str 字段在这种情况下不相关。

来自hiredis文档：

The number of elements in the multi bulk reply is stored in reply->elements.
Every element in the multi bulk reply is a redisReply object as well
and can be accessed via reply->element[..index..].
Redis may reply with nested arrays but this is fully supported.

所以你的代码应该修改如下：

reply = redisCommand(redis, "MGET %s %s", "foo", "name" );
if ( reply->type == REDIS_REPLY_ERROR )
  printf( "Error: %s\n", reply->str );
else if ( reply->type != REDIS_REPLY_ARRAY )
  printf( "Unexpected type: %d\n", reply->type );
else 
{
  int i;
  for ( i=0; i<reply->elements; ++i )
    printf( "Result: %s\n", reply->element[i]->str );
}
freeReplyObject(reply);

有了这个改变，现在的输出是：

SET foo bar: OK
SET name value: OK
Result: bar
Result: value

注意：不需要释放每个单独的元素，因为 freeReplyObject 会删除整个树。