Really world-wide variable

Ephracis · 12-14-2004, 05:27 PM

I made a server that uses MySQL as database and I guess that it wouldn't be good to connect again, and again, and again whenever I need to get data. The main-function uses threads to "split up" whenever it gets a connection but I thought it would be best to have only one connection to the database throughout the whole server.

So that's why the connection should be directly when the server starts up and the connection would be closed when the server dies.

Here is how I connects to the server:

Code:

mysqlcppapi::Connection con;
con.set_Host("127.0.0.1");
con.set_User("root");
con.connect();
con.select_database("operation_m");

After this I use the "con" variable to create a query and execute the query and so on. So all other files (C++ source code files) just need the variable "con".

How should I design main to make the variable able to all the other files that need to access the database?

dakensta · 12-14-2004, 07:10 PM

use extern

iirc,

in the header file put
extern mysqlcppapi::Connection con

in an implementation file call a constructor (you need to compile this!)
mysqlcppapi::Connection con;
or
mysqlcppapi::Connection con(/* ctor args */)

include the header file in any other files that need access to 'con'

perform any extra initialisation in some initialisation function called before anything else in main to setup the object, open connections etc.

If you get it wrong you will get linker errors, giving you stuff like:
multiple definitions of con

(addendum)
You can re-declare the variable in other files where it is needed with:
extern mysqlcppapi::Connection con

but the important part is that there is only one definition (and in c++ declaration is definition, unless you have that extern there).