How to select different db execution "keys *"

[YuanlvCold]

redisReply * _reply;

 _reply = (redisReply*)redisCommand(_redisCxt, "select 1");
 _reply = (redisReply*)redisCommand(_redisCxt, "keys *");

if (_reply->type == REDIS_REPLY_ARRAY){
        for (int i = 0; i < _reply->elements; ++i){
             _reply->element[i]->str;
        }
}

question：
The keys I got are all in the database db0.
I need to select different db to get all keys at the same time, what do I need to do. thanks!

[bjosv]

Using select 1 is the correct way to tell Redis that the client wants to use logical db 1.
Either the Redis instance has been setup as a cluster node (select is not supported in cluster mode) or there are other errors.
One suggestion in to make sure the first redisCommand(select 1) results in a non-null reply, and is of type REDIS_REPLY_STATUS and str is OK.

[michael-grunder]

As @bjosv says, you should check to make sure the SELECT command is not returning an error.

#include <hiredis/hiredis.h>
#include <string.h>
#include <assert.h>

#include <hiredis/hiredis.h>
#include <string.h>
#include <assert.h>

int main(void) {
    redisContext *_redisCtx;
    redisReply *_reply;

    _redisCtx = (redisContext*)redisConnect("localhost", 6379);
    assert(_redisCtx != NULL && _redisCtx->err == 0);

    _reply = (redisReply*)redisCommand(_redisCtx, "select 1");
    assert(_reply != NULL && _reply->type == REDIS_REPLY_STATUS &&
           _reply->len == 2 && !strcmp(_reply->str, "OK"));
    freeReplyObject(_reply);

    _reply = (redisReply*)redisCommand(_redisCtx, "keys *");
    assert(_reply != NULL && _reply->type == REDIS_REPLY_ARRAY);

    for (size_t i = 0; i < _reply->elements; i++) {
        assert(_reply->element[i]->type == REDIS_REPLY_STRING);
        printf("KEY[%zu]: %s\n", i, _reply->element[i]->str);
    }

    freeReplyObject(_reply);
    redisFree(_redisCtx);
}

Cluster mode being enabled is the most likely issue (as it disables database numbers) but you can also verify this via redis-cli.

I'm going to close this issue since it's unlikely to be a bug in hiredis but I'm happy to help you figure it out. 😄

[YuanlvCold]

Using select 1 is the correct way to tell Redis that the client wants to use logical db 1. Either the Redis instance has been setup as a cluster node (select is not supported in cluster mode) or there are other errors. One suggestion in to make sure the first redisCommand(select 1) results in a non-null reply, and is of type REDIS_REPLY_STATUS and str is OK.

Your reply solved my problem. Thank you!

[YuanlvCold]

As @bjosv says, you should check to make sure the SELECT command is not returning an error.

#include <hiredis/hiredis.h>
#include <string.h>
#include <assert.h>

#include <hiredis/hiredis.h>
#include <string.h>
#include <assert.h>

int main(void) {
    redisContext *_redisCtx;
    redisReply *_reply;

    _redisCtx = (redisContext*)redisConnect("localhost", 6379);
    assert(_redisCtx != NULL && _redisCtx->err == 0);

    _reply = (redisReply*)redisCommand(_redisCtx, "select 1");
    assert(_reply != NULL && _reply->type == REDIS_REPLY_STATUS &&
           _reply->len == 2 && !strcmp(_reply->str, "OK"));
    freeReplyObject(_reply);

    _reply = (redisReply*)redisCommand(_redisCtx, "keys *");
    assert(_reply != NULL && _reply->type == REDIS_REPLY_ARRAY);

    for (size_t i = 0; i < _reply->elements; i++) {
        assert(_reply->element[i]->type == REDIS_REPLY_STRING);
        printf("KEY[%zu]: %s\n", i, _reply->element[i]->str);
    }

    freeReplyObject(_reply);
    redisFree(_redisCtx);
}

Cluster mode being enabled is the most likely issue (as it disables database numbers) but you can also verify this via redis-cli.

I'm going to close this issue since it's unlikely to be a bug in hiredis but I'm happy to help you figure it out. 😄

Through the example you gave, I checked my code and found that reply->len==43, when "select %s", a vector parameter value forgot to convert to c_str(). Thank you!