Using true and false in C

Question

As far as I can see there are 3 ways to use booleans in c

1. with the bool type, from then using true and false
2. defining using preprocessor #define FALSE 0 ... #define TRUE !(FALSE)
3. Just to use constants directly, i.e. 1 and 0

are there other methods I missed? What are the pros and cons of the different methods?

I suppose the fastest would be number 3, 2 is more easily readable still (although bitwise negation will slightly add to overhead), 1 is most readable not compatible with all compilers.

Answer 1

I used to use the #define because they make code easier to read, and there should be no performances degradation compared to using numbers (0,1) coz' the preprocessor converts the #define into numbers before compilation. Once the application is run preprocessor does not come into the way again because the code is already compiled.

BTW it should be:

#define FALSE 0 
#define TRUE 1

and remember that -1, -2, ... 2, 3, etc. all evaluates to true.

Answer 2

I don't know you specific situation. Back when I was writing C programs, we have always used #2.

#define FALSE = 0
#define TRUE = !FALSE

This might be otherwise under alien platform to DOS or Intel-based processors. But I used to use both C and ASM together writing graphic libraries and graphical IDE. I was a true fan of Micheal Abrash and was intending to learn about texture mapping and so. Anyway! That's not the subject of the question here!

This was the most commonly used form to define boolean values in C, as this headerfile stdbool.h did not exist then.