You may cast away the constness of b1 and modify the value to which it refers. Because the memset function takes a non- const pointer to void , the compiler must implicitly cast away const. Their cast is resolved at compile time. NET Core 3 Packages. Jul 15, at 3: Right, that was confused. Unfortunately, this reduces the priority of applying the recommendation because it makes more sense to fix problems that are easier to fix, but which have the same severity and likelihood. I thought what Doug was saying was that there was another valid exception to this guideline which I added as an exception to this guideline.
Jul 15, at 2: A name with internal linkage at global namespace scope is visible only within the component that has the name. A much better approach is to tell the truth in your header file, by applying the keyword mutable correctly, as shown in Listing 4. Undefined behavior only occurs when the const variable is being modified. Permalink Apr 18, Modifying the value is another story, though. Lets say I’m using a framework which returns me the width of a mobile device width differs from device to device At the class construction the width isn’t calculated so i can’t init the correct calculated value in the initiaizer list , but the framework offers a OnInit method and at this point the GetWidth method returns the correct device width. A number of C standard library functions are specified to return non- const pointers that refer to their const -qualified arguments.
P, or if there is a better solution: I’d be happy to add a new rule or resuscitate EXPC. And as I write this article, the example hasn’t yet been provided. On the other hand, trying to modify const variable though non-const pointer is undefined behavior.
Jul 17, at 6: You’re creating a non-const pointer called This and pointing it at the instance for which getValue was called, then using the non-const pointer to change the values of the member cxst. Well, I’m talking from memory, so can’t give specifics why it was done or if it’s still in Qt’s code.
Permalink Mar 16, Last edited on Jul 13, at 2: John unfortunately you can’t do what I posted then without causing UB. Sometimes, cached values are always correct, because you invalidate the cache consness you do something that means the value isn’t right any more; but other times, the cached value might be incorrect, and you just hope it’s not incorrect by very much.
Even though the pointer is not constattempting to modify the character it points to would lead to undefined awway.
If the intention is to allow the array values to be modified, do not declare the array as const:.
Ergo, a global object with internal linkage is preferable to a private static member object. Do not access a volatile object through a non-volatile reference: Sign up using Email and Password.
Correa Correa 1 9. I need to violate that const ness on two occassions, once to store virgin data to it:. I actually wrote that rule and never quite understood the objections to it, although alot of folks did seem to find some fault.
Qualifier removed in conversion. Ergo, a private static member object is preferable to a global object with external linkage. My mistake; I should have written static int value constnesd. Casting away the const qualification allows a program to modify the object referred to by the pointer, which may result in undefined behavior. Without knowing what any of this is, you can see that getValue doesn’t change any member variables, and neither does Cosntness.
The const_cast operator (C++ only)
Can detect violations of this recommendation when the -Wcast-qual flag is used. In your case I’d say yes, you should try to make it const. You need a value to be a non-static aay object of the class only if the value can vary from instance to instance. Once you’ve made this cast, you can do whatever you like with that This pointer.
const_cast conversion –
But it doesn’t hold universally — people throughout a company might update their timesheets many times a day with a journaling app, but management might only look at waay totals once or twice a week, for example. Results of changing a variable which was originally const are undefined.
Jul 17, at TorKlingberg on July 25, As to casting away const-ness in other contexts, usually it’s a mistake, but not always. Do you want to create the new rule or do you want me to? However, if you cast away the constness of an object that has not been explicitly declared as constyou can modify it safely.
EXPC. Do not cast away a const qualification – SEI CERT C Coding Standard – Confluence
Yes, if a variable is declared const, casting away const-ness from a pointer to it and then writing to it is undefined. The width of the mobile device is the same for every instance, isn’t it? It’s a subset of caching.
So I thought I’d provide one. You would const static data only if the program never modifies it Now imagine I show you that getValue looks like this:. I think it’s a reasonable idea, but I have never seen anyone use const in that way before. You may also be able to cannibalize this rule EXPC. With a private non-static const volatile member object, many optimisations are inhibited: