Difference between string literal and constexpr array of char

Question

I have been wondering if there is any difference between what is being pointed by ptrToArray and ptrToLiteral in the following example:

constexpr char constExprArray[] = "hello";
const char* ptrToArray = constExprArray;

const char* ptrToLiteral = "hello";

Is my understanding that constExprArray and the two "hello" literals are all compile time constant lvalues correct?
If so, is there any difference in how they are stored in the executable file, or is it purely compiler implementation or platform specific?
Are they treated differently at runtime behind the scenes?
Anything else to know about?

Andrew Tomazos · Accepted Answer · 2014-03-21 05:11:07Z

33

A string literal and a constexpr array of char are almost identical. A pointer to either is an address constant expression. An lvalue-to-rvalue conversion is permitted on their elements in a constant expression. They both have static storage duration. The only difference that I know of is that a string literal can initialize an array whereas a constexpr array cannot:

constexpr char a[] = "hello";

constexpr char b[] = a; // ill-formed
constexpr char b[] = "hello"; // ok

To get around this you can wrap the array in a class of literal type. We are currently looking at standardizing such a wrapper that will be called std::string_literal or similar, but for now you will have to do this by hand.

answered Mar 21, 2014 at 5:11

Andrew Tomazos

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