Appending a number to enum to get other enum

Question

I want to get the enum value in a for loop, by appending a number, like

enum example
{
Example_1,
Example_2,
Example_3,
.
.
.
Example_n
};
example x;
for (i = 0; i < n; i++
{x = Example_ + i; // if i = 5, I need Example_5
}

I want this implementation in C++11

I already have enums in place which are widely used across my codebase. So can't change to array. — Naren, May 08 '20 at 06:34
You might want to look at https://stackoverflow.com/a/57346836/2466431 — JVApen, May 08 '20 at 08:12

score 2 · Accepted Answer · answered May 08 '20 at 06:34

2

If you have an Example_0 in the enum, then Example_0 + 5 will give you an integer value equivalent to Example_5. Enums are just integers.

All this assuming that you don't explicitly assign a value to a certain enumeration constant - that's another story.

answered May 08 '20 at 06:34

Lundin

195,001
40
254
396

There are other enumrations in between, so I can use as you suggested. There is no proper offset between these specified enums – Naren May 08 '20 at 06:53
1

@Naren Then kindly _post the actual enum_ so that your question can be answered. – Lundin May 08 '20 at 06:54
The enumeration definition looks like: enum example { Example_1, Temp_0, Example_2, Temp_1, Temp_2, Apple_1, Example_3 } – Naren May 08 '20 at 07:05

score 0 · Answer 2 · answered May 08 '20 at 08:34

You cannot concatenate name with number to retrieve enum name and use enum value.

With contiguous enum, you can use simple arithmetic.

you can create operator++ for your enum, resolve by switch:

example operator++(example e)
{
    switch (e) {
    case Example_1: return Example_2;
    case Example_2: return Example_3;
    case Example_3: return Example_4;
    // ...
    case Example_n: return Last;
    };
    throw std::runtime("value out of range");
}

and so, possibly

for (example e = Example_1: e != Last; ++e) {/*..*/}

using array to provide enum list:

constexpr auto AllExamples() {
    constexpr std::array res{{Example_1,
                              Example_2,
                              /*..*/,
                              Example_n}};
    return res;
}

which allows:

for (auto ex : AllExamples()) {/*..*/}
f(AllExamples()[5]);

or use map if you really have to play with names:

std::map<std::string, example> ExamplesAsMap() {
    return {
        {"Example_1", Example_1},
        {"Example_2", Example_2},
        /*..*/
        {"Example_n", Example_n},
        {"Value_1", Value_1},
        {"Value_2", Value_2},
        /*..*/
        {"Value_n", Value_n}
        /**/
    };
}

And then

const auto m = ExamplesAsMap();
example x;
for (int i = 0; i < n; i++) {
    x = m.at("Example_" + std::to_string(i));
    // ...
}

Appending a number to enum to get other enum

2 Answers2