Qt and REDIS interface [SOLVED]

[xtingray]

Hi,
I wonder if some of you have experience using any kind of C/C++ API for REDIS from Qt. Right now I have to implement a basic interface between a Qt application and a REDIS database, but I can't find any useful documentation about it.
A couple of days ago I started to study the project Hiredis [ https://github.com/redis/hiredis/ ] looking for a starting point and as far as it is a C API I guess it should be possible to call it from Qt, right?

I really appreciate any hint on this matter. Thanks.

[SGaist]

Hi,

I haven't used REDIS yet but a quick search shows several projects using Qt to talk to a REDIS database like Redis Desktop

In any case, you can use C libraries with Qt (e.g. doable with ffmpeg so...)

[xtingray]

Thanks for the advice!

By the way, I decided to try the integration between Qt and the library Hiredis by myself and finally I could make it work. It's really simple after you find out the key details you must care about.
Some hints:

1. About your .pro file. You need to include the headers and the libraries of Hiredis in your project, taking care of the installation path. For example:
   INCLUDEPATH += /opt/local/include
   LIBS += -L/opt/local/lib -lhiredis

2. About the Qt classes where you want to call Hiredis functions. You should care about including the Hiredis headers in the right way:
   extern "C" {
   #include "hiredis/hiredis.h"
   }

From this point, you should be able to call any Hiredis function from your Qt code. Now, if you want more information about the Hiredis API, I recommend you to check the examples code available at https://github.com/redis/hiredis/tree/master/examples

I hope this can be useful for someone else! :)

[SGaist]

Thanks for sharing.

By the way, if you wrote a nice wrapper for Qt, it can be worth sharing it also

[Duncan]

@xtingray

Hello!

When i try to issue commands from Qt to redis server i get the following error: 35: error: assigning to 'redisReply *' from incompatible type 'void *'
reply = redisCommand(c,"PING");
^ ~~~~~~~~~~~~~~~~~~~~~~
When i do a "client list" command I see another connection, I just don't know why I cant send commands.

Below are the files I am using:

#include "mainwindow.h"
#include "ui_mainwindow.h"
// #include "hiredis.h"
extern "C"
{
#include "hiredis.h"
}

#include <QDebug>

using namespace std;

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    redisReply *reply;

    long int i;


    //redisContext *redisConnect(const char *ip, int port);
    //void *redisCommand(redisContext *c, const char *format, ...);
    // void freeReplyObject(void *reply);

    redisContext *c = redisConnect("127.0.0.1", 6379);
    if (c != NULL && c->err)
    {
        printf("Error: %s\n", c->errstr);
        // handle error
    }

      reply = redisCommand(c,"PING");
      printf("PING: %s\n", reply->str);
      freeReplyObject(reply);

  /* reply = redisCommand(c, "keys %s", "*");
        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
        {
            for ( i=0; i < 5 ; ++i )
            {
                   printf( "Result:%lu: %s\n", i,
                          reply->element[i]->str );
            }
        }
        printf( "Total Number of Results: %lu\n", i );

 //   qDebug << reply; */



}

MainWindow::~MainWindow()
{
    delete ui;
}

#-------------------------------------------------
#
# Project created by QtCreator 2015-06-22T12:56:46
#
#-------------------------------------------------

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets


INCLUDEPATH += /MultimediaOSX/hiredis-master

LIBS += -L/MultimediaOSX/hiredis-master -lhiredis


TARGET = TestHiredis
TEMPLATE = app


SOURCES += main.cpp\
        mainwindow.cpp

HEADERS  += mainwindow.h

FORMS    += mainwindow.ui

Thanks for your help!

[xtingray]

Well, I made exactly the same error you did and this is because the hredis documentation is a little tricky/messy. Now, this is how I had to deal with commands:

    QString command = "GET variable";
    QByteArray bytes = command.toLocal8Bit();
    redisReply *reply;
    void *pointer = NULL;

    pointer = redisCommand(context, bytes.constData()); // You must define "context" previously
    reply = (redisReply*)pointer;
    QString result = QString(reply->str);
    QDebug() << "Result: " << result;
    freeReplyObject(reply);

Maybe not so elegant, but it works to me. I hope this could help you in some way :)

[Duncan]

@xtingray

This helped a bunch, I got it to work !!!!

Thanks you sir for your time,

Duncan

[DendyGema]

This post is deleted!