Using true and false in C

Question

As far as I can see there are 3 ways to use booleans in c   with the bool type  from  then using true and false defining using preprocessor  define FALSE 0      define TRUE   FALSE  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

User · Answer

There is no real speed difference  They are really all the same to the compiler  The difference is with the human beings trying to use and read your code   For me that makes bool  true  and false the best choice in C   code  In C code  there are some compilers around that don t support bool  I often have to work with old systems   so I might go with the defines in some circumstances

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I would go for 1  I haven t met incompatibility with it and is more natural  But  I think that it is a part of C   not C standard  I think that with dirty hacking with defines or your third option - won t gain any performance  but only pain maintaining the code

User · Answer

Just include  lt stdbool h gt  if your system provides it  That defines a number of macros  including bool  false  and true  defined to  Bool  0  and 1 respectively   See section 7 16 of C99 for more details

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1 is most readable not compatible with all compilers    No ISO C compiler has a built in type called bool   ISO C99 compilers have a type  Bool  and a header  which typedef s bool   So compatability is simply a case of providing your own  header if the compiler is not C99 compliant  VC   for example    Of course a simpler approach is to compile your C code as C

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I usually do a   typedef enum  FALSE   0  TRUE  boolean

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Whichever of the three you go with  compare your variables against FALSE  or false   Historically it is a bad idea to compare anything to true  1  in c or c    Only false is guaranteed to be zero  0   True is any other value     Many compiler vendors have these definitions somewhere in their headers       define TRUE 1  define FALSE 0   This has led too many people down the garden path     Many library functions besides chartype return nonzero values not equal to 1 on success  There is a great deal of legacy code out there with the same behavior

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I prefer to use    define FALSE  0  0    define TRUE   0  0    or directly in the code  if  flag     0  0             The compiler will take care of that  I use a lot of languages and having to remember that FALSE is 0 bothers me a lot  but if I have to  I usually think about that string loop   do         while   ptr     and that leads me to see that FALSE is 0

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I prefer the third solution  i e  using 1 and 0  because it is particularly useful when you have to test if a condition is true or false  you can simply use a variable for the if argument  If you use other methods  I think that  to be consistent with the rest of the code  I should use a test like this   if  variable    TRUE               instead of   if  variable

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Any int other than zero is true  false is zero   That way code like this continues to work as expected   int done   0        int  could be  bool  just as well  while   done                     done   OS SUCCESS CODE    some system call         IMO  bool is an overrated type  perhaps a carry over from other languages   int works just fine as a boolean type

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You can test if bool is defined in c99 stdbool h with   ifndef   bool true false are defined      bool true false are defined    0   typedef or define here  endif

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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

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With the stdbool h defined bool type  problems arise when you need to move code from a newer compiler that supports the bool type to an older compiler  This could happen in an embedded programming environment when you move to a new architecture with a C compiler based on an older version of the spec    In summation  I would stick with the macros when portability matters  Otherwise  do what others recommend and use the bulit in type

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Just use 0 or 1 directly in the code    For C programmers  this is as intuitive as true or false

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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

User · Answer

I prefer  1  when i define a variable but in expressions i never compare against true and false just take the implicit C definition of if flag  or if  flag  or if ptr   Thats the C way to do things

[c] Using true and false in C

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