Q: How can I construct preprocessor #if expressions which compare strings?
A: You can't do it directly; preprocessor #if arithmetic uses only integers. An alternative is to #define several macros with symbolic names and distinct integer values, and implement conditionals on those:
#define RED 1 #define BLUE 2 #define GREEN 3 #if COLOR == RED /* red case */ #else #if COLOR == BLUE /* blue case */ #else #if COLOR == GREEN /* green case */ #else /* default case */ #endif #endif #endif(Standard C specifies a new #elif directive which makes if/else chains like these a bit cleaner.)
See also question 20.17.
References:
K&R2 Sec. 4.11.3 p. 91
ISO Sec. 6.8.1
H&S Sec. 7.11.1 p. 225
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