Question

I have legacy code that is using an enum as a range and iterating through the range. I need to port this to a new platform and make it safer.

Note: enums are not safe to iterate through as there may be “holes” or gaps between values.

I’m looking for a safe C language pattern for a range type.

For example, given a range (RED, VIOLET, BLUE, GREEN, YELLOW, ORANGE), I want to iterate through each value, like “FOR color IN (RED, VIOLET, BLUE, GREEN, YELLOW, ORANGE)”.

When I search SO and the web, I get replies about the range of a data type, such as the range of an integer.

This code will reside on an embedded system that uses an ARM7 processor.

Answer 1

An enum can do just fine, as long as you let the compiler choose values. This way, there would be no holes. You could, for example, do this:

enum colors {
    FIRST_COLOR=0,
    RED=FIRST_COLOR, VIOLET, BLUE, GREEN, YELLOW, ORANGE,
    NUM_COLORS
}

enum colors color;
for (color=FIRST_COLOR; color<NUM_COLORS; color++) {
    // whatever
}

And a quote from the ANSI C standard:

If the first enumerator has no = , the value of its enumeration
constant is 0. Each subsequent enumerator with no = defines its
enumeration constant as the value of the constant expression obtained
by adding 1 to the value of the previous enumeration constant