C++ Access numbered variables

Question

We have numbered variables like:

float my_float_0;
float my_float_1;
float my_float_2;

Is there any form of template / macro magic that would let us access these variables by index in a for loop?

The variable names are auto-generated from external; using arrays instead is sadly not an option. — jonnie, Aug 25 '17 at 12:38
Whatever auto-generated that does not appear to be particularly useful. — Baum mit Augen, Aug 25 '17 at 12:40
Naive macro solution: `#define MY_FLOAT_(i) my_float_##i` `for (int i = 0; i <= 2; ++i) MY_FLOAT_(i) = i;` — 0x5453, Aug 25 '17 at 12:54

score 1 · Answer 1 · answered Aug 25 '17 at 12:40

If you have no control over the variables, your only option is some good ol' macro metaprogramming. Boost.Preprocessor's documentation is a good place to start - you can iterate over a range of numbers and concatenate them with the my_float_ token to produce your variable names.

Example (untested):

#define SEQ (0)(1)(2)
#define MACRO(r, data, elem) BOOST_PP_CAT(elem, data)

BOOST_PP_SEQ_FOR_EACH(MACRO, my_float_, SEQ) 
// expands to my_float_0 my_float_1 my_float_2

By changing what MACRO expands to, you can generate code for each variable.

C++ Access numbered variables

1 Answers1