Hi, I often need to convert/cast integer variables to double for multiplication/division: int a = 10; int b = 3; double c = static_cast<double>(a) / b; In general I use a static_cast , but I also think this is quite ugly to read. To convert the type there are of course multiple ways: int a = 10; int b = 3; double c = static_cast<double>(a) / b; double d = double(a) / b; double e = (double)a / b; I think the best for reading the code is double d = double(a) / b; . But I don't know if there's a difference and when to use which.

@J.Hilk said in Number Type Cast : actually no, Actually yes. Almost all errors that fall in the -fpermissive are there to prevent you from shooting yourself in the foot. The compiler can compile it just fine, hence the existence of the aforementioned flag. As a matter of fact if you try it with MSVC you're (probably with surprise) going to realize that it eats it just fine - no errors, just a warning or so. as int my be a smaller type than a pointer ;-) So? Substitute void * with long long and see what happens ... pure magic ... Truncation is unimportant here, and truncation is not an error by the way. Don't we have const_cast for the above mentioned cases ? Indeed, and some compilers may just allow you to static_cast it too depending on the types and how the compiler's implemented. However, here's a better snippet for your consideration: typedef void* voidp; const int * x; void * y = static_cast<voidp>(x); // Case 1 void * z = voidp(x); // Case 2 Case 1 is an error, because you're trying to const_cast and static_cast at the same time, Case 2 is valid and compiles fine. Most of the time this is harmless, obviously, as with the case of primitive types, but, and I repeat again, there's no semantic difference between C-style casts and constructor-style casts; they are exactly the same thing.

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Number Type Cast

Solved C++ Gurus

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S SGaist
8 Apr 2019, 07:19

@beecksche said in Number Type Cast:

MyDerivedClass derived = static_cast<MyDerivedClass>(base);

Just one note: static_cast has absolutely no notion of safety. There's no check involved so you are completely responsible to ensure that the type you are casting to is really is valid with regard to the type you are casting from.

dynamic_cast does check and in the case of pointers return a null pointer that you can validate before continuing your code.
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beecksche

wrote on 9 Apr 2019, 03:15 last edited by

#21

@jsulm , @SGaist

thanks a lot. I thought I had understood the problem. But it seems to be a bit more complicated.

Hopefully, in some time, I will understande when to use which cast explicitly and for what reason.

Until thenI hope that these parts of the code don't make any trouble.
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9 Apr 2019, 03:15