Double pointer const-correctness warnings in C

by

The reason why const can only be added one level deep is subtle, and is explained by Question 11.10 in the comp.lang.c FAQ.

Briefly, consider this example closely related to yours:

const int i;
int *p;
int const **z = &p;
*z = &i;
/* Now p points to i */

C avoids this problem by only allowing assignment to discard qualifiers at the first pointed-to level (so the assignment to z here is not allowed).

Your exact example does not suffer from this problem, because the const the second level means that the assignment to *z would not be allowed anyway. C++ would allow it in this exact case, but C’s simpler rules do not distinguish between your case and the example above.

More Related Contents:

  1. Sum of the all the numbers between a and b [closed]
  2. “static const” vs “#define” vs “enum”
  3. What is the difference between char * const and const char *?
  4. Can we change the value of an object defined with const through pointers?
  5. Can a const variable be used to declare the size of an array in C?
  6. Why can’t I convert ‘char**’ to a ‘const char* const*’ in C?
  7. Why is this happening with the sizeof operator when comparing with a negative number? [duplicate]
  8. Constant pointer vs Pointer to constant [duplicate]
  9. In C, can a const variable be modified via a pointer?
  10. Where are constant variables stored in C?
  11. Variably modified array at file scope
  12. Why can I change a local const variable through pointer casts but not a global one in C?
  13. Why am I being allowed to use a const qualified variable as an array size in C?
  14. __attribute__((const)) vs __attribute__((pure)) in GNU C
  15. Unsigned hexadecimal constant in C?
  16. Unable to free const pointers in C
  17. How to initialize const in a struct in C (with malloc)
  18. const usage with pointers in C
  19. Confusion regarding modification of const variable using pointers
  20. Should useless type qualifiers on return types be used, for clarity?
  21. Strange warning in a C function const multidimensional-array argument
  22. Why can I change the value of a const char* variable?
  23. Deep Analysis of Const Qualifier in C
  24. constness and pointers to pointers
  25. How is this const being used?
  26. hexadecimal floating constant in C
  27. Is the sizeof(enum) == sizeof(int), always?
  28. Integer conversions(narrowing, widening), undefined behaviour
  29. What is the difference between static const and const?
  30. Is it Undefined Behaviour to cast away the constness of a function parameter?

Leave a Comment