Is using char as a bool in C bad practice?

Question

Is there any downside to using

typedef char bool;
enum boolean { false, true };

in C to provide a semantic boolean type?

Answer 1

In C99, you should be using stdbool.h , which defines bool , true , and false .

Otherwise what you have is fine. Using just the enum may be a bit simpler, but if you really want to save space what you have works.

Answer 2

The short answer is: it's fine. It's particularly good if you needed to make large arrays of them, although I would be tempted to just use the C99 built-in ¹ .

Since you asked "is there any downside..." I suppose I could remark that there have been important machines that did not actually have a character load instruction. (The Cray and initial DEC Alpha come to mind.) Machines in the future may suddenly go all minimal once again.

It will always be fast to load a standard integral type.

It will probably always be fast to load a single character.

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^{1. See C99 6.2.5. There is a built-in type _Bool . Then, if you include <stdbool.h> (see C99 7.16) you get an alias, the more gracefully named bool , and defines for true and false . If you use this it will clash with your typedef but I'm sure it would be an easy thing to fix.}

Answer 3

The downside of typedef char bool; is that if you compile with a C99 implementation and happen to include <stdbool.h> , this ends up as typedef char _Bool; , which is wrong. Also, if you ever tried to compile the code as C++, you'd have issues (that's not necessarily a problem, but it could be).

It would probably better either to use <stdbool.h> if your implementation provides one or to use a different name for the type, like BOOL .

Answer 4

I would suggest using a bit to represent true or false, rather than a character. A character uses 8 bits, We can set 1 for true and 0 for false with just 1 bit. That will be more memory efficient and also satisfies the purpose. (eg) char flag:1;

Reference : http://en.wikipedia.org/wiki/Bit_field