cwl157

i have a 2d int array that i want to access from across files.

i have heard of making a variable extern but don't really know what that means. If i put it in a .h file and then include that .h file i get an error saying more then 1 has been defined. Is there a way without classes for me to be able to access the same 2d int array from more then one file. The reason i dont want a class is because this is the only file i need to access across files. Functions in the other file modify this 2d int array so if i could have it set up somewhere and then let all the other functions access it by including a .h file or something i think that would be ideal. So basically i want to make a int 2d array global across files. I think there is a way to check if something is already defined in a header file is that what im looking for maybe? Thanks.

Ancient Dragon

The extern keyword means that the variable will be actually declared somewhere else. So in the *.h file use extern and in one, and only one, *.c or *.cpp file declare it again but without the extern keyword. You don't have to put it in a *.h file, instead you can do it like this:

__________________
I Like Ike. Vote for Dwight Eisenhower this November.
--This message brought to you by the the Procrastinators Club Of America.

cwl157

so by using extern in one file and then just declaring it normally in another it will be using the same variable in both files right? I want the same 2d int array to be updated from 2 different files so does this make 2 copies of the array or just a way to access the same array from 2 different files? Actually how then would i access the same array from 3 or more different files. You said i could delcare it in 1 other place is there a way i would be able to declare it in more then 2 places?

Ancient Dragon

When you declare it as extern in all but one *.cpp file there is only ONE copy of the array regardless of how many *.c or *.cpp files there are. Update the array from one *.cpp file and the changes will be visible in all *.cpp files.

If this is still a little confusing to you, create yourself a little program that has three *.cpp files and test out what I said. Put print statements in each *.cpp file to display the value of the array after it has been changed by that *.cpp file.

__________________
I Like Ike. Vote for Dwight Eisenhower this November.
--This message brought to you by the the Procrastinators Club Of America.

cwl157

Oh ok so as long as in each .cpp file you declare it extern then it will use the same one. That makes sense