I have a simple c file (mylib.so)compiled as a .so on Mac. This file has two global variables, one is an integer and the other is a pointer pointing to heap. From outside the .so, i.e..from another file (myapp.c) I see that I can access the global integer variable defined inside the .so but when I try to access the pointer, its value is NULL. I have declared both as externs in myapp.c. Was wondering why the global pointer is NULL ?
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Top comments (3)
Who is responsible to initializing your pointer?
You should have something like an init method in mylib.c to initialize it.
Could you share some code?
It's a bad design anyway, why do you need a global variable in your library?
A better design would be to have a "context structure" containing the data and make the methods of your library work on this structure.
Now you can use this context in your app.
Note: it lacks error handling in my example.
I'm not sure it answers your question here but in a general sense you shouldn't rely on global variables. You could make one static context struct for your library in myLib.cc also.
Thanks a lot for your reply. This is definitely much better than using global variables directly. Since it didnt work, I too had something similar to what you have mentioned. I had getter functions to access the global pointer. I still want to know why exactly the global pointer was NULL. Since the lib and the app both are part of same memory space. Here is a snippet which had the problem.
struct node *pHead;
node *add_new_head(int val)
pHead = malloc();
extern node *pHead;
//add, move , delete nodes
node *itr = pHead
global variables are initialized to 0 by default because they are stored in a different section of memory than automatic variables.