C printing boolean what is displayed

Question

I print a bool to an output stream like this    include  lt iostream gt   int main         std  cout  lt  lt  false  lt  lt  std  endl      Does the standard require a specific result on the stream  e g  0 for false

User · Answer

0 will get printed   As in C   true refers to 1 and false refers to 0   In case  you want to print false instead of 0 then you have to sets the boolalpha format flag for the str stream   When the boolalpha format flag is set  bool values are inserted extracted by their textual representation  either true or false  instead of integral values    include  lt iostream gt  int main       std  cout  lt  lt  std  boolalpha  lt  lt  false  lt  lt  std  endl      output   false   IDEONE

User · Answer

The standard streams have a boolalpha flag that determines what gets displayed -- when it s false  they ll display as 0 and 1  When it s true  they ll display as false and true   There s also an std  boolalpha manipulator to set the flag  so this    include  lt iostream gt   include  lt iomanip gt   int main         std  cout lt  lt false lt  lt   n       std  cout  lt  lt  std  boolalpha         std  cout lt  lt false lt  lt   n       return 0         produces output like   0 false   For what it s worth  the actual word produced when boolalpha is set to true is localized--that is   lt locale gt  has a num put category that handles numeric conversions  so if you imbue a stream with the right locale  it can will print out true and false as they re represented in that locale  For example     include  lt iostream gt   include  lt iomanip gt   include  lt locale gt   int main         std  cout imbue std  locale  fr          std  cout  lt  lt  false  lt  lt    n       std  cout  lt  lt  std  boolalpha      std  cout  lt  lt  false  lt  lt    n       return 0         and at least in theory  assuming your compiler standard library accept  fr  as an identifier for  French   it might print out faux instead of false  I should add  however  that real support for this is uneven at best--even the Dinkumware Microsoft library  usually quite good in this respect  prints false for every language I ve checked   The names that get used are defined in a numpunct facet though  so if you really want them to print out correctly for particular language  you can create a numpunct facet to do that  For example  one that  I believe  is at least reasonably accurate for French would look like this    include  lt array gt   include  lt string gt   include  lt locale gt   include  lt ios gt   include  lt iostream gt   class my fr   public std  numpunct lt  char  gt    protected      char do decimal point   const   return            char do thousands sep   const   return            std  string do grouping   const   return   3         std  string do truename   const   return  vrai          std  string do falsename   const   return  faux         int main         std  cout imbue std  locale std  locale    new my fr         std  cout  lt  lt  false  lt  lt    n       std  cout  lt  lt  std  boolalpha      std  cout  lt  lt  false  lt  lt    n       return 0      And the result is  as you d probably expect    0 faux

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