Should I better use global variables?

Question

I want to use GMainLoop. I wonder if it is better to use global or local variables. I want to call a function every 5 secs. It uses some heap variables and I want to malloc only once. I have two ideas. I can put all arguments in a struct. But sometimes it would be struct in struct in struct. So the name nomenclature will be complex and bad readable. I can also make all data gloal. It would be something like:

typedef struct data_t
{
  unsigned char *pUncompressStreamData;
  unsigned char *pStartUncompressStreamData
  analyzers_t analyzers;
  GTree *tree;
}data_t;
main_loop(data_t data )
{
   //data_mallocs and other stuff
} 
int main()
{
    data_t data;

    g_timeout_add_seconds ( 5, main_loop, data);
    /free all data member
} 

OR

unsigned char *pUncompressStreamData;
unsigned char *pStartUncompressStreamData
analyzers_t analyzers;
GTree *tree;

main_loop(data_t data )
{
   //data_mallocs and other stuff
} 
int main()
{

    g_timeout_add_seconds ( 5, main_loop, NULL);
    /free all data member
} 

Please give me clues.

Answer 1

Use local variables or structures (more readable and more modular). Notice that you could pass them, e.g. as the address of some struct, as the client data of g_timeout_add_seconds. So prefer the first version to the second. However, you main should initialize data e.g. with calloc then free it after the Glib event loop.