A foolproof approach to maintain number-to-string mappings. No more name mapping headache.

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?
Nov 27 2013
Touchless enum to string
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3. Why
For machines, numbers are natural,
but,
For humans, names are natural.
Nov 27 2013
Touchless enum to string
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4. Why
(Log) Message:
Error: Device 1234 (cdrom)
failed.
Ooops…
aha! the cdrom
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Touchless enum to string
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5. What
Number to Name
need
unique
bidirectional
(1:1)
mapping
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Touchless enum to string
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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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Touchless enum to string
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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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Touchless enum to string
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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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Touchless enum to string
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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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Touchless enum to string
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10. How
Solution:
Define (number, name) pair in a
separate file
COLOR_DEF( ColorRed, “Red”)
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Touchless enum to string
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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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Touchless enum to string
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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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Touchless enum to string
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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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Touchless enum to string
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15. Thank you!
Comments are much appreciated
Arun Saha
http://www.linkedin.com/in/arunksaha
Nov 27 2013
Touchless enum to string
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