IOS extern usage tutorial

IOS development uses extern to access global variables

Use the extern keyword method:

 1. Create a new constants. h file (the file name can be retrieved as needed) to store global variables;

 2. Write the required global variable name in constants. h, but do not initialize it during definition. Otherwise, an error occurs, for example:

                  Nsstring * URL; // pointer type
                Int count; // non-pointer type

 3, Introduce this file in the file that requires the use of global variables:

                # Import "Constants. H"  

       4. initialize or assign values to global variables:

1. Extern nsstring * URL;
3. Url = [[nsstring alloc] initwithformat: @ "http://www.hbcfg.net"]; // pointer type; alloc required
5. Extern int count;
7. Count = 0; // non-pointer type

      The use of global variables is the same as that of common variables.

Of course, there are other methods: You can declare and initialize global variables in appdelegate, and use a single instance to access global variables.