C++11/C++14 constexpr ans string literals - 2020

"If you're an experienced C++ programmer and are anything like me, you initially approached C++11 thinking, "Yes, yes, I get it. It's C++, only more so." But as you learned more, you were surprised by the scope of the changes. auto declarations, range-based for loops, lambda expressions, and rvalue references change the face of C++, to say nothing of the new concurrency features. And then there are the idiomatic changes. 0 and typedefs are out, nullptr and alias declarations are in. Enums should now be scoped. Smart pointers are now preferable to built-in ones. Moving objects is normally better than copying them.
- Effective Modern C++ by Scott Meyers

C++ has always had the concept of constant expressions.

These are expressions such as 3+4 that will always yield the same results, at compile time and at run time. Constant expressions are optimization opportunities for compilers, and compilers frequently execute them at compile time and hardcode the results in the program.

// C++03
int a[5];          // OK
int f() { return 7; }  // OK
int a[5 + f()];    // compile error

// C++11
constexpr int g() { return 7; }  // OK
int b[5 + g()];    // create an array of 12 ints (note: vs2013RC doesn't seem to support this)

// C++03
char* a = "string";

// C++11
char *    a = u8"string";   // UTF-8 string
char16_t* b = u"string";    // UTF-16
char32_t* c = U"string";    // UTF-32
char*     r = R"string";    // raw string

C++11/C++14 New Features