Writing binary number system in C code

Question

As we use 0x prefix for hexadecimal numbers  and 0 for octal ones  is there anything that can be done for binary numbers   I tried the b suffix  but the GCC didn t allow it      Error  invalid suffix  b  on integer constant   Is it possible

User · Answer

Prefix you literal with 0b like in  int i   0b11111111    See here

User · Answer

Standard C doesn t define binary constants  There s a GNU  I believe  extension though  among popular compilers  clang adapts it as well   the 0b prefix   int foo   0b1010    If you want to stick with standard C  then there s an option  you can combine a macro and a function to create an almost readable  binary constant  feature    define B x  S to binary   x   static inline unsigned long long S to binary  const char  s            unsigned long long i   0          while   s                    i  lt  lt   1                  i     s   -  0                     return i      And then you can use it like this   int foo   B 1010     If you turn on heavy compiler optimizations  the compiler will most likely eliminate the function call completely  constant folding  or will at least inline it  so this won t even be a performance issue   Proof   The following code    include  lt stdio h gt   include  lt stdlib h gt   include  lt limits h gt   include  lt string h gt     define B x  S to binary   x   static inline unsigned long long S to binary  const char  s        unsigned long long i   0      while   s            i  lt  lt   1          i     s   -  0             return i     int main         int foo   B 001100101        printf   d n   foo        return 0      has been compiled using clang -o baz S baz c -Wall -O3 -S  and it produced the following assembly        section      TEXT   text regular pure instructions      globl   main      align  4  0x90  main                                       main      cfi startproc    BB 0      pushq    rbp Ltmp2       cfi def cfa offset 16 Ltmp3       cfi offset  rbp  -16     movq     rsp   rbp Ltmp4       cfi def cfa register  rbp     leaq    L  str1  rip    rdi     movl     101   esi                   lt   This line      xorb     al   al     callq    printf     xorl     eax   eax     popq     rbp     ret      cfi endproc       section      TEXT   cstring cstring literals L  str1                                      str1      asciz     d n     subsections via symbols   So clang completely eliminated the call to the function  and replaced its return value with 101  Neat  huh

User · Answer

Use BOOST BINARY  Yes  you can use it in C      include  lt boost utility binary hpp gt      int bin   BOOST BINARY 110101     This macro is expanded to an octal literal during preprocessing

[c] Writing binary number system in C code

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