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
– jonnie, Commented Aug 25, 2017 at 12:38
Whatever auto-generated that does not appear to be particularly useful. — Baum mit Augen
– Baum mit Augen ♦, Commented Aug 25, 2017 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
– 0x5453, Commented Aug 25, 2017 at 12:54

Vittorio Romeo · Accepted Answer · 2017-08-25 12:40:25Z

1

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.

answered Aug 25, 2017 at 12:40

Vittorio Romeo

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