What is the printf format specifier for bool

Question

Since ANSI C99 there is  Bool or bool via stdbool h  But is there also a printf format specifier for bool   I mean something like in that pseudo code   bool x   true  printf   B n   x     which would print   true

User · Answer

To just print 1 or 0 based on the boolean value I just used:

printf("%d\n", !!(42));

Especially useful with Flags:

#define MY_FLAG (1 << 4)
int flags = MY_FLAG;
printf("%d\n", !!(flags & MY_FLAG));

User · Answer

ANSI C99 C11 don t include an extra printf conversion specifier for bool   But the GNU C library provides an API for adding custom specifiers   An example    include  lt stdio h gt   include  lt printf h gt   include  lt stdbool h gt   static int bool arginfo const struct printf info  info  size t n      int  argtypes  int  size      if  n        argtypes 0    PA INT       size   sizeof bool         return 1    static int bool printf FILE  stream  const struct printf info  info      const void  const  args      bool b      const bool   args 0      int r   fputs b    true     false   stream     return r    EOF   -1    b   4   5     static int setup bool specifier       int r   register printf specifier  B   bool printf  bool arginfo     return r    int main int argc  char   argv      int r   setup bool specifier      if  r  return 1    bool b   argc  gt  1    r   printf  The result is   B n   b     printf   written  d characters  n   r     return 0      Since it is a glibc extensions the GCC warns about that custom specifier      gcc -Wall -g    main c   -o main main c  In function    main     main c 34 3  warning  unknown conversion type character    B    in format  -Wformat      r   printf  The result is   B n   b        main c 34 3  warning  too many arguments for format  -Wformat-extra-args    Output        main The result is  false  written 21 characters      main 1 The result is  true  written 20 characters

User · Answer

There is no format specifier for bool types  However  since any integral type shorter than int is promoted to int when passed down to printf   s variadic arguments  you can use  d   bool x   true  printf   d n   x      prints 1   But why not   printf x    true     false      or  better   printf   s   x    true     false      or  even better   fputs x    true     false   stdout     instead

User · Answer

There is no format specifier for bool  You can print it using some of the existing specifiers for printing integral types or do something more fancy    printf   s   x  true   false

User · Answer

If you like C   better than C  you can try this    include  lt ios gt   include  lt iostream gt   bool b   IsSomethingTrue    std  cout  lt  lt  std  boolalpha  lt  lt  b

User · Answer

In the tradition of itoa      define btoa x    x   true   false    bool x   true  printf   s n   btoa x

User · Answer

You can t  but you can print 0 or 1   Bool b   1  printf   d n   b     source

User · Answer

I prefer an answer from Best way to print the result of a bool as   39 false  39  or   39 true  39  in c   just like  printf   s n    false 0true  6 x      x    0   false 0true   0  it means  false   x    1   false 0true   6  it means  true

[c++] What is the printf format specifier for bool?

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