how to make a pointer to array of structs global

Question

I have this code :

#define N 100  //starting size of the array

int is_full(VERTEX *arr);
int add_vertex(char *name);
int print_degree(int ID);
int _get_vertex(int ID);
VERTEX *resize_array(VERTEX *vertex_array,int new_size);

VERTEX *arr = (VERTEX*)calloc(N, sizeof(VERTEX)); // dynamic allocation and initialization to NULL\0

int main(void)
{
    int vertex_counter = 0 ;
    int starting_size_of_array = sizeof(VERTEX)*N;
}

I get the error : error C2099: initializer is not a constant

I want the VERTEX array to be global - in order for me to access this array anywhere . so how come it's not constant? N is under #define , and VERTEX has it's declaration in th .h file.

Konrad Rudolph · Accepted Answer · 2020-01-21 13:50:48Z

3

First off, the initialiser isn’t a constant. You need to initialise the global from within a function – e.g. main:

VERTEX *arr;

int main(void)
{
    arr = calloc(N, sizeof *arr);
}

But you should not use globals in the first place, if avoidable (and it usually is). It destroys your code design.

edited Jan 21, 2020 at 13:50

answered May 27, 2012 at 9:47

Konrad Rudolph

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4 Comments

user1386966 Over a year ago

but then dor example if I have a function that adds a vertex , how can I reach this arr without passing it as a parameter?

Konrad Rudolph Over a year ago

@user1386966 You can’t, you pass it as a parameter. That’s the correct thing to do.

user1386966 Over a year ago

the problem is than my function is : void add_vertex(char * name) -homework stuff, so I can't pass another parameter

Konrad Rudolph Over a year ago

@user1386966 Ah. Sucks. In that case, take the solution I wrote in my answer.

Unknown1987 · Accepted Answer · 2012-05-27 09:47:26Z

0

The value calloc() will return is not constant. You can init arr to NULL then initialize it during your program start up.

answered May 27, 2012 at 9:47

Unknown1987

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