CODEWITHSUNDEEP
c++gcccompiler-warningsconstexprstring-literals
digito_evo
digito_evo

Reputation: 3672

constexpr causes a GCC warning when used with string literal

The below code compiles:

#include <iostream>


int main( )
{
    const char* const str = "This is a constant string.";

    std::cout << str << '\n';
}

However, this one gives a warning:

    constexpr char* const str = "This is a constant string.";

Here:

warning: ISO C++ forbids converting a string constant to 'char*' [-Wwrite-strings]
   37 |         constexpr char* const str = "This is a constant string.";
      |                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~

Is this a bug in GCC? I'm converting a string to a pointer that is pointing to a constexpr char array. Is this warning valid?

Now making the pointer itself constexpr prevents it from being compiled at all:

    const char* constexpr str = "This is a constant string.";

Here:

error: expected unqualified-id before 'constexpr'
   37 |         const char* constexpr str = "This is a constant string.";
      |                     ^~~~~~~~~

Why can't a pointer be constexpr?

Upvotes: 0

Views: 259

Answers (1)

Andreas Loanjoe
Andreas Loanjoe

Reputation: 2399

Whether or not you are using constexpr here is not the issue. You are trying to store a string literal in a char* const which is not a pointer to immutable data (which the string literal is), but rather a pointer with a constant address. A string literal can be stored as const char* or const char* const instead.

const char* str = "This is a constant string."

Adding constexpr would look like this:

constexpr const char* str = "This is a constant string."

Upvotes: 3

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