How to print result of a compile-time calculation in C++?

Question

I\'ve wrote several constexpr functions and use them in static_asserts to control some resource limits. But I\'d like to not only enforce compile-time predicate but also to

Answer 1

There's an answer by @je4d (https://stackoverflow.com/a/13465643/3353857),
which works for msvc, gcc, clang, and lots of compilers on godbolt except for the ancient gcc 4.1.2

#define strcat_(x, y) x ## y
#define strcat(x, y) strcat_(x, y)
#define PRINT_VALUE(x) \
    template  \
    struct strcat(strcat(value_of_, x), _is); \
    static_assert(strcat(strcat(value_of_, x), _is)::x, "");


#line 4242
constexpr int PI_INT = __LINE__;  /*set the value*/

PRINT_VALUE(PI_INT) /*print it*/

It prints the value in the error message:

:4244:1: error: incomplete type 'value_of_PI_INT_is<4242>' used in nested name specifier