Global pointer in C
c, interpreter, pointers, scheme
Solution
It looks like you are trying to `malloc` when you should just use global data. You could try
struct conscell globalEnvironment;
Just remember to never `free` it.
If you need to have a pointer handle so you can push cells on the list:
struct conscell _globalEnvironment;
List globalEnvironment = &_globalEnvironment;
Still, remember to never `free` `_globalEnvironment`.
Problem
I am new to C and I am currently implementing a Scheme interpreter in C. I am close to the end but a problem is bothering me which I have not been able to tackle yet. I want a "globalEnvironment" pointer to a struct which stays throughout the time the program runs and gets modified too (not a constant). ``` /**************************************************************** Creates the List as a pointer to the conscell structure */ typedef struct conscell *List; /**************************************************************** Creates a conscell structure, with a char pointer (symbol) and two pointers to * conscells (first and rest) */ struct conscell { char *symbol; struct conscell *first; struct conscell *rest; }; List globalEnvironment; /**************************************************************** Function: globalVariables() -------------------- This function initializes the global variables */ void globalVariables() { globalEnvironment = malloc(sizeof (struct conscell)); globalEnvironment->symbol = NULL; globalEnvironment->first = NULL; globalEnvironment->rest = NULL; } ``` As you can see "List" is a pointer to a conscell structure. So all I want is the globalEnvironment List to be global. The problem is that I cannot do malloc there. If I try the following: ``` List globalEnvironment = malloc(sizeof (struct conscell)); ``` instead of just "List globalEnvironment;" it gives an error that "initialiser element is not a constant" To tackle this situation, I created a new function "globalVariables" which runs at the beginning of the program, initialises globalEnvironment and allocates it memory. It is not working as I expected though and I keep getting segmentation fault errors for other functions that I have not written here to keep it simple. Is there another, simpler, way to declare a pointer (not constant) to a structure in C? Hope someone can help, Thank you