I am attempting to use WordPress functions with php, and i am getting some troubles..

the mistake message states: Call to undefined method stdClass::set_prefix() in /hd2/www/WWW_BACKUP/www-lalala/blog/wordpress-configurations.php online 287

I am unsure why you would like to integrate the 2, as Wordpress isn't a development framework. I'm creating a Large assumption that you will wish to simply have it within the same 'directory' and have the ability to make use of the same database?

I have seen so now before, also it involves simply discussing config files for the database (include wordpress config inside codeigniter, etc).

Just stick CI in the folder within your Wordpress directory:

  /ci/ (codeigniter runs inside here)
  index.php (wordpress)
  .htaccess (combined wordpress / ci functionality)

You would then just duck within the /ci folder for CI functionality and redirect to Wordpress after.

So far as integrating with merge of CODE (ie, wordpress with CI running within it or the other way around) that's pointless and many would argue a total waste of time.

Wordpress already offers the majority of the features you would like to build in CI (session monitoring / database active querying / fundamental CRUD functionality / user management).

If whatever you seek would be to utilize some small 'functions' in Wordpress that you will get in CI, I'd say concentrate on porting individuals alone.

Nothing good may come individuals merging two programs together such as this.