Skip to main content

const/volatile integrity violation

This time I am going to point you at two short, interesting articles on const integrity violation which is also applicable to volatile modifier.

Basically it talks about the following feature of C++:

GIVEN
int *i;

const int *p = i; // is allowed
BUT
const int** p = &i; // is not allowed !!
AND
const int*& p = i; // is also not allowed !!

How to fix it?

GIVEN
int *i;

const int *p = i; // is allowed
BUT
const int* const * p = &i; // is allowed !!
AND
const int* const & p = i; // is also allowed !!


FAQ:
http://www.parashift.com/c++-faq-lite/const-correctness.html#faq-18.17
AND
http://www.gimpel.com/html/bugs/bug1561.htm

Comments

stunned said…
Astonshing blog. I relished in the site and you
know I will be going to it again! Surfing the internet
hepls me to find blogs that arfe just as good.
Check out the blog site with my coupon 1800contacts in it!
Exciting blog. Your site was amazing and will be
back again! I never get tired of looking for blogs
just like this one.
Come as you are and look at my coupon 1800contacts blog.
after-while said…
Striking blog. I liked the site I will be back
again! Websurfing is a good way to find blogs like
yours.
In my spare time I will look for your coupon 1800contacts blog.

Popular posts from this blog

Multi-dimensional arrays in C++11

What new can be said about multi-dimensional arrays in C++? As it turns out, quite a bit! With the advent of C++11, we get new standard library class std::array. We also get new language features, such as template aliases and variadic templates. So I'll talk about interesting ways in which they come together.

It all started with a simple question of how to define a multi-dimensional std::array. It is a great example of deceptively simple things. Are the following the two arrays identical except that one is native and the other one is std::array?

int native[3][4];
std::array<std::array<int, 3>, 4> arr;

No! They are not. In fact, arr is more like an int[4][3]. Note the difference in the array subscripts. The native array is an array of 3 elements where every element is itself an array of 4 integers. 3 rows and 4 columns. If you want a std::array with the same layout, what you really need is:

std::array<std::array<int, 4>, 3> arr;

That's quite annoying for two r…

Folding Monadic Functions

In the previous two blog posts (Understanding Fold Expressions and Folding Functions) we looked at the basic usage of C++17 fold expressions and how simple functions can be folded to create a composite one. We’ll continue our stride and see how "embellished" functions may be composed in fold expressions.

First, let me define what I mean by embellished functions. Instead of just returning a simple value, these functions are going to return a generic container of the desired value. The choice of container is very broad but not arbitrary. There are some constraints on the container and once you select a generic container, all functions must return values of the same container. Let's begin with std::vector.
// Hide the allocator template argument of std::vector. // It causes problems and is irrelevant here. template <class T> struct Vector : std::vector<T> {}; struct Continent { }; struct Country { }; struct State { }; struct City { }; auto get_countries…

Covariance and Contravariance in C++ Standard Library

Covariance and Contravariance are concepts that come up often as you go deeper into generic programming. While designing a language that supports parametric polymorphism (e.g., templates in C++, generics in Java, C#), the language designer has a choice between Invariance, Covariance, and Contravariance when dealing with generic types. C++'s choice is "invariance". Let's look at an example.
struct Vehicle {}; struct Car : Vehicle {}; std::vector<Vehicle *> vehicles; std::vector<Car *> cars; vehicles = cars; // Does not compile The above program does not compile because C++ templates are invariant. Of course, each time a C++ template is instantiated, the compiler creates a brand new type that uniquely represents that instantiation. Any other type to the same template creates another unique type that has nothing to do with the earlier one. Any two unrelated user-defined types in C++ can't be assigned to each-other by default. You have to provide a c…