indirection in structures. 1

[denc4]

my problem is the following:

  main()
  {
    struct STRUCTURE
    {
      int *integer;
    } a;
    int *integer;

    *integer = 1;            /* success */
    a.*integer = 1;          /* error */
  }

why can't i use the indirection operator on a structure member? my compiler just says "syntax error '*'" at the second integer assignment..

thx.

 

[xwb]

*(a.integer) = 1;

 

[denc4]

thanx, surprisingly simple solution. i should have thought of that..

doesn't indirection have a higher priority than value assignment?? i tested your solution with, and without the parenthesis, both work and have the same effect.

 

[Salem]

Yes, assignment is pretty close to the bottom of the heap in precedence terms

http://www.cppreference.com/operator_precedence.html

Any good C book will have this table in one form or another.

--

 

[xwb]

I just use parenthesis just to be absolutely sure because I've been caught out so many times. I've also had to fix lots of bugs where precedence was a problem, especially with the post increment/decrement. For instance, I've seen

*xx++ = --*yy;

If there is a bug in this area, there are many possible interpretations. I just prefer to do it long hand i.e. something like

--(*yy);
*xx = *yy;
xx++;

so I know exactly what is happening and to be in control of the order in which it happens. If you are absolutely sure of page 52 in K&R, fine but I can never remember it so I take the safe route.