Question

I have a global var struct:

typedef struct {
    int myvar1;
    int myvar2;
    int myvar3;
    ...
    int myvar10;
} t_myStruct myGlobalData;

I cannot avoid this global structures, so I have to use it.
I have three options to use it:

• Use the global var “as is” into any function. I.e.:

  int myFunc(void) {
      myGlobalData.myvar1 = ...
      myGlobalData.myvar10 = myGlobalData.myvar5 + ...
  }
  

• Declare a local pointer and use it:

  int myFunc(void) {
      t_myStruct * p;
  
      p = &myGlobalData;
      p->myvar1 = ...
      ...
      p->myvar10 = p->myvar5 + ...
  }
  

• Use local var and then copy to global struct:

  int myFunc(void) {
      t_myStruct localStruct;
  
      localStruct.myvar1 = ...
      localStruct.myvar10 = localStruct.myvar5 + ...
      myGlobalData = localStruct ;
  }
  

Could explain me what is best way in general and why?

Answer 1

Choose more abstraction. If you can change the arguments to myFunc, then make its signature:

int myFunc(t_myStruct *arg)
{
    arg->myvar1 = ...

Now the function itself doesn’t depend on the existence of a global variable at all. And the same for any other functions that need to operate on a struct of this type. If you must use a global variable then isolate the use of it as much as possible, i.e. use the global in as few places as possible.

If you can’t change the function signature, I would choose the option from your question that is the most direct: the first. Just operate directly on the global variable.