CODEWITHSUNDEEP
c++c++11staticconstantsconstexpr
hg_git
hg_git

Reputation: 3084

static, constexpr, const - what do they mean when all used together?

I'm totally frustrated with these specifiers because I understand what they do when they're by themselves but I find them hard to understand when they're used with each other. For example, some code in the wild contained - 

namespace{
static constexpr char const *Hello[] = { "HelloString", "WorldString"};
...
}

what does this even do?

And worst of all, it compiles :/. Ofcourse it would compile because they're valid statements, but what does it even means?

Upvotes: 7

Views: 922

Answers (1)

Weak to Enuma Elish
Weak to Enuma Elish

Reputation: 4637

Why use static when you're already inside an anonymous namespace?

I don't see a reason to here, unless it is written for C++03 compatibility.

Why use constexpr - there's no reason to use it here. wouldn't a simple const would do?

Again, it isn't necessary here, but it does indicate that it is a compile time constant. Also note that constexpr here means the pointer is constexpr, and removes the need for const after the * (see next part).

const *Hello doesn't makes sense to me. What is constant here? The strings or the pointer *Hello?

const applies to the left, unless there is nothing there in which case it applies to the right. const to the left of * means the pointer when dereferenced is a constant, while to the right means it is a constant pointer to something.

char const * ptr = "Foo";
ptr[0] = 'B'; //error, ptr[0] is const

char * const ptr = "Foo";
ptr = new char[10]; //error, ptr is const

char const * const ptr = "Foo"; //cannot assign to either ptr or *ptr
constexpr char const* ptr = "Foo"; //same as above, constexpr replaced last const

I found that this page on the "right left" rule really helps with understanding complicated declarations.

Upvotes: 6

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