Touchless

enum to string

in C

Arun Saha

No more enum mapping headaches

(Log) Message: Error: Device 1234 failed.

What is device 1234, btw, any name?

Why

Nov 27 2013 Touchless enum to string 2

For machines, numbers are natural, but,

For humans, names are natural.

Why

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(Log) Message: Error: Device 1234 (cdrom)

failed.

Ooops… aha! the cdrom

Why

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Number to Name need

unique bidirectional

(1:1) mapping

What

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Mapping Example

ColorCode (enum)

<->

ColorName (char const *)

Translation API /// Map Number -> Name

ColorName colorName( ColorCode );

/// Map Name -> Number

ColorCode colorCode( ColorName );

What

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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))

How

Nov 27 2013 Touchless enum to string 7

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.

How

Nov 27 2013 Touchless enum to string 8

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.

How

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Solution: Define (number, name) pair in a

separate file

COLOR_DEF( ColorRed, “Red”)

How

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Solution: Define (number, name) pair in a

separate file as macro

#define COLOR_DEF( ColorRed, “Red”)

How

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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Solution Insight: Different Macro Expansion

.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,

How

Nov 27 2013 Touchless enum to string 12

color_defs.h

COLOR_DEF( ColorRed, "Red" )

COLOR_DEF( ColorYellow, "Yellow" )

COLOR_DEF( ColorGreen, "Green" )

color.c

static const ColorName colorNames[] = {

"First",

#define COLOR_DEF( number, name ) name,

#include "color_defs.h"

#undef COLOR_DEF

"Last"

};

.h file:

Expand macro to get number in enum

.c file:

Expand macro to get name in array

How

color.h

typedef enum ColorCode {

ColorFirst = 0,

#define COLOR_DEF( number, name ) number,

#include "color_defs.h"

#undef COLOR_DEF

ColorLast

} ColorCode;

Code available at github https://github.com/arunksaha/enum_to_string

How

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Thank you!

Comments are much appreciated

Arun Saha

http://www.linkedin.com/in/arunksaha

Nov 27 2013 Touchless enum to string 15