How to run Redis sadd commands with hiredis - c++

Question

My code contains a head file redis.h and a c++ source file redis.cpp.
This is a demo of sadd opeaion in redis. All the operations fail, becase of WRONGTYPE Operation against a key holding the wrong kind of value. I don't know what happened.
Please give me some suggestions.
//redis.h
#ifndef _REDIS_H_
#define _REDIS_H_
#include <iostream>
#include <string.h>
#include <string>
#include <stdio.h>
#include <hiredis/hiredis.h>
using namespace std;
class Redis{
public:
Redis(){}
~Redis(){
this->_connect =NULL;
this->_reply=NULL;
}
bool connect(string host, int port){
this->_connect = redisConnect(host.c_str(), port);
if(this->_connect != NULL && this->_connect->err){
printf("connect error: %s\n", this->_connect->errstr);
return 0;
}
return 1;
}
string set(string key, string value){
this->_reply = (redisReply*)redisCommand(this->_connect, "sadd %s %s", key.c_str(), value.c_str());
string str = this->_reply->str;
return str;
}
string output(string key){
this->_reply = (redisReply*)redisCommand(this->_connect, "smembers %s", key.c_str());
string str = this->_reply->str;
freeReplyObject(this->_reply);
return str;
}
private:
redisContext * _connect;
redisReply* _reply;
};
#endif //_REDIS_H
//redis.cpp
#include "redis.h"
int main(){
Redis *r = new Redis();
if(!r->connect("127.0.0.1", 6379)){
printf("connect error!\n");
return 0;
}
printf("Sadd names Andy %s\n", r->set("names", "Andy").c_str());
printf("Sadd names Andy %s\n", r->set("names", "Andy").c_str());
printf("Sadd names Alice %s\n", r->set("names", "Alice").c_str());
printf("names members: %s\n", r->output("names").c_str());
delete r;
return 0;
}
The result:
Sadd names Andy WRONGTYPE Operation against a key holding the wrong kind of value
Sadd names Andy WRONGTYPE Operation against a key holding the wrong kind of value
Sadd names Alice WRONGTYPE Operation against a key holding the wrong kind of value
names members: WRONGTYPE Operation against a key holding the wrong kind of value

Answer 1

WRONGTYPE Operation against a key holding the wrong kind of value
This means the key, i.e. names, has already been set, and its type is NOT a SET. You can run TYPE names with redis-cli to see the type of the key.
Also, your code has several problems:
redisConnect might return null pointer
you did not call redisFree to free the resource of redisReply in your set method
sadd and smembers do NOT return string reply, so you cannot get the correct reply
Since you're using C++, you can try redis-plus-plus, which is based on hiredis, and have more C++ friendly interface:
try {
auto r = sw::redis::Redis("tcp://127.0.0.1:6379");
r.sadd("names", "Andy");
r.sadd("names", "Alice");
std::vector<std::string> members;
r.smembers("names", std::back_inserter(members));
} catch (const sw::redis::Error &e) {
// error handle
}
Disclaimer: I'm the author of redis-plus-plus.