Is const_cast safer than normal cast?

Question

Which is safer to use?

int main()
{
    const int i=5;
    int *ptr;
    ptr=(int*)&i; <------------------- first

    ptr=const_cast<int*>(&i); <-------------------Second
    return 0;
}

Probably neither, but if you run into a situation where you're absolutely forced to, `const_cast` is more explicit as to what you're doing. — chris, Jul 27 '12 at 00:06

score 8 · Accepted Answer · answered Jul 27 '12 at 00:09

It's safer in the sense that you won't get a cast that's something other than just removing const:

int main()
{
    const char i=5;
    int *ptr;
    ptr=(int*)&i;  // the compiler won't complain

    ptr=const_cast<int*>(&i); // will fail, since `i` isn't an int
    return 0;
}

which doesn't necessary mean that the const_cast<> is safe:

const int i=5;

int main()
{
    int const& cri(i);

    int& ri = const_cast<int&>(cri);  // unsafe

    ri = 0; // will likely crash;

    return 0;
}

score 2 · Answer 2 · answered Jul 27 '12 at 00:08

They are entirely equivalent, except that C-style casts present more of a maintenance headache over the const_cast. If the code were frozen in time, they would be identical. The Standard says that the C-style cast may devolve to static, reinterpret, or const cast or a combination of the three, or a strange funky cast that can access private bases for some reason. The point is, in this use case it is exactly equivalent to const_cast.

score 1 · Answer 3 · answered Jul 27 '12 at 00:07

1

I'm not sure about safety - I'm sure someone is more well-versed in this than I am - but C++-style casts are part of the language standard and should always be preferred over C-style casts (as a matter of both style as well as readability).

~~To amend my answer, it appears that C++-style casts are checked by the compiler whereas C-style casts fail at runtime; in that regard, C++-style casts are definitely safer.~~

answered Jul 27 '12 at 00:07

David Titarenco

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Nope, they are completely identical. – Puppy Jul 27 '12 at 00:09
http://stackoverflow.com/questions/1609163/what-is-the-difference-between-static-cast-and-c-style-casting - that (highly-upvoted) answer is erroneous then ;s – David Titarenco Jul 27 '12 at 00:10

score 1 · Answer 4 · answered Jul 27 '12 at 00:09

Neither is safer than the other. In both cases undefined behavior will occur should you modify the value through one of the pointers that have been casted. const_cast has the benefit of doing only what you want and expresses it clearly, while the C style cast could be everything and is not sensitive to the actual type of its argument.

score 1 · Answer 5 · answered Jul 27 '12 at 00:20

It's safer, but in a different way than you imagine.

It's safer because you explicitly state you're casting away constness.

When someone sees your code, they think - "ok, here's a const_cast, this argument must have been const. Let's take a closer look at this", whereas a regular cast just gets lost in the back of the mind when reading big chunks of code.

Is const_cast safer than normal cast?

5 Answers5