CODEWITHSUNDEEP
c++11constexprstatic-assert
SPMP
SPMP

Reputation: 1223

Static assert on size of static const member

I'm trying to put a static assert on the size of static const unordered_map member. But I get an error saying non-const condition for static assertion. Could someone help?

#include<unordered_map>
#include<string>

using namespace std;    

class A{
    public:
    static const unordered_map<string,string> strMap;
};

const unordered_map<string,string> A::strMap ={{"key","value"}};

int main() {
static_assert(A::strMap.size() == 1, "sizes don't match");
}

EDIT: Based on the comments, I want to clarify, the following code works fine (it uses an array instead of a map):

#include<unordered_map>
#include<string>

using namespace std;    

class A{
    public:
    static const pair<string,string> strMap[];
};

const pair<string,string> A::strMap[] ={{"key","value"}};

int main() {
//static_assert(sizeof(A::strMap)/sizeof(A::strMap[0]) == 2, "sizes don't match");  Fails to compile
static_assert(sizeof(A::strMap)/sizeof(A::strMap[0]) == 1, "sizes don't match"); //Compiles fine
}

Upvotes: 2

Views: 1528

Answers (1)

SergeyA
SergeyA

Reputation: 62603

Can't do this. You'd need constexpr std::unordered_map for this, and this is not possible, since it's constructor is not constexpr. And of course, no class which allocates memory (unordered_map being of this kind) can declare it's constructor constexpr.

Upvotes: 4

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