This document presents a solution for mapping enumerations to strings in C code in a way that is robust to changes. The author proposes defining (number, name) pairs for enum values in a separate header file using macros. The macros are expanded differently in header and source files to populate the enum numbers and string names arrays respectively. This avoids issues with separate definition of numbers and names and maintains a clean 1:1 mapping. The approach works by defining macros that expand to either the number or name based on the file type for robust and synchronized definition of the enumeration mapping.

1. Touchless
enum to string
in C
No more enum mapping headaches
Arun Saha

2. Why
(Log) Message:
Error: Device 1234 failed.
What is device 1234,
btw, any name?
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Touchless enum to string
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3. Why
For machines, numbers are natural,
but,
For humans, names are natural.
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4. Why
(Log) Message:
Error: Device 1234 (cdrom)
failed.
Ooops…
aha! the cdrom
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5. What
Number to Name
need
unique
bidirectional
(1:1)
mapping
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6. What
Mapping Example
ColorCode (enum)
<->
ColorName (char const *)
Translation API
/// Map Number -> Name
ColorName colorName( ColorCode );
/// Map Name -> Number
ColorCode colorCode( ColorName );
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7. How
Attempt #1: Array of strings
Numbers defined as enum
Names defined as array of char const *
In array of names, position/index of a string is same
as its code.
(A minor variation is to use a switch statement on the number (ColorCode))
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8. How
Attempt #1: Array of strings
In the array, position/index of a string
is same as its code.
Issue 1: The sequence in the array is
dependent on the sequence in the
enum, any out of order element
messes up the mapping.
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9. How
Attempt #1: Array of strings
In the array, position/index of a string
is same as its code.
Issue 2: For a (number, name) pair, the number
and the name are defined in two separate files;
out of sync file pair (e.g. maintainer added
enum in one file but missed to add name in the
other file) garbles the mapping.
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10. How
Solution:
Define (number, name) pair in a
separate file
COLOR_DEF( ColorRed, “Red”)
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11. How
Solution:
Define (number, name) pair in a
separate file as macro
#define COLOR_DEF( ColorRed, “Red”)
The author avoids macro as much as possible, but the current situation
is a good usage of macro, which is hard to obtain otherwise.
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12. Solution Insight:
Different Macro Expansion
How
.h file:
• Expand macro to get number in enum
• #define COLOR_DEF(number, name) number,
.c file:
• Expand macro to get name in array
• #define COLOR_DEF(number, name) name,
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13. How
.h file:
Expand macro to get number in enum
color.h
typedef enum ColorCode {
ColorFirst = 0,
#define COLOR_DEF( number, name ) number,
#include "color_defs.h"
#undef COLOR_DEF
ColorLast
} ColorCode;
color_defs.h
COLOR_DEF( ColorRed, "Red" )
COLOR_DEF( ColorYellow, "Yellow" )
COLOR_DEF( ColorGreen, "Green" )
color.c
.c file:
Expand macro to get name in array
static const ColorName colorNames[] = {
"First",
#define COLOR_DEF( number, name ) name,
#include "color_defs.h"
#undef COLOR_DEF
"Last"
};

14. How
Code available at github
https://github.com/arunksaha/enum_to_string
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15. Thank you!
Comments are much appreciated
Arun Saha
http://www.linkedin.com/in/arunksaha
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