CODEWITHSUNDEEP
c++c++17
eof
eof

Reputation: 153

Checking that macro parameter is one of the allowed ones?

I'd like to accomplish something like the following:

#define FOO(bar, ...) \
  static_assert(bar == "foo" || bar == "bazz", "Invalid value for bar") \
  ...

In other words, I'd like to check at compile time that the value given to the macro is one of the allowed ones. What is the cleanest way for doing a compile time string comparison when comparing against strings of variable length?

Upvotes: 3

Views: 193

Answers (1)

Indiana Kernick
Indiana Kernick

Reputation: 5331

You could use string views.

#include <string_view>

using namespace std::string_view_literals;

// Note the sv after the string
#define FOO(bar, ...) \
  static_assert(bar == "foo"sv || bar == "bazz"sv, "Invalid value for bar") \
  ...

The expression "foo"sv invokes a literal operator. It constructs a std::string_view from "foo". std::string_view has overloaded == operators for comparing with strings. These overloaded operators are constexpr which means that they can be evaluated at compile time.

Upvotes: 3

Related Questions