Static constant string (class member)

Question

I'd like to have a private static constant for a class (in this case a shape-factory).

I'd like to have something of the sort.

class A {
   private:
      static const string RECTANGLE = "rectangle";
}

Unfortunately I get all sorts of error from the C++ (g++) compiler, such as:

ISO C++ forbids initialization of member ‘RECTANGLE’

invalid in-class initialization of static data member of non-integral type ‘std::string’

error: making ‘RECTANGLE’ static

This tells me that this sort of member design is not compliant with the standard. How do you have a private literal constant (or perhaps public) without having to use a #define directive (I want to avoid the uglyness of data globality!)

Any help is appreciated.

user_931726 · Answer

possible just do:

static const std::string RECTANGLE() const {
    return "rectangle";
}

or

#define RECTANGLE "rectangle"

Admin · Answer

Fast forward to 2018 and C++17.

do not use std::string, use std::string_view literals
please do notice the 'constexpr' bellow. This is also an "compile time" mechanism.
no inline does not mean repetition
no cpp files are not necessary for this

static_assert 'works' at compile time only

using namespace std::literals;

namespace STANDARD {
constexpr 
inline 
auto 
compiletime_static_string_view_constant() {
// make and return string view literal
// will stay the same for the whole application lifetime
// will exhibit standard and expected interface
// will be usable at both
// runtime and compile time
// by value semantics implemented for you
    auto when_needed_ =  "compile time"sv;
    return when_needed_  ;
}

};

Above is a proper and legal standard C++ citizen. It can get readily involved in any and all std:: algorithms, containers, utilities and a such. For example:

// test the resilience
auto return_by_val = []() {
    auto return_by_val = []() {
        auto return_by_val = []() {
            auto return_by_val = []() {
return STANDARD::compiletime_static_string_view_constant();
            };
            return return_by_val();
        };
        return return_by_val();
    };
    return return_by_val();
};

// actually a run time 
_ASSERTE(return_by_val() == "compile time");

// compile time 
static_assert(
   STANDARD::compiletime_static_string_view_constant() 
   == "compile time" 
 );

Enjoy the standard C++

Static constant string (class member)

11 Answers