How to print using cout a number in binary form

Question

I m following a college course about operating systems and we re learning how to convert from binary to hexadecimal  decimal to hexadecimal  etc  and today we just learned how signed unsigned numbers are stored in memory using the two s complement   number   1   We have a couple of exercises to do on paper and I would like to be able to verify my answers before submitting my work to the teacher  I wrote a C   program for the first few exercises but now I m stuck as to how I could verify my answer with the following problem  char a  b   short c  a   -58  c   -315   b   a  gt  gt  3   and we need to show the binary representation in memory of a  b and c  I ve done it on paper and it gives me the following results  all the binary representations in memory of the numbers after the two s complement    a   00111010  it s a char  so 1 byte  b   00001000  it s a char  so 1 byte  c   11111110 11000101  it s a short  so 2 bytes   Is there a way to verify my answer  Is there a standard way in C   to show the binary representation in memory of a number  or do I have to code each step myself  calculate the two s complement and then convert to binary   I know the latter wouldn t take so long but I m curious as to if there is a standard way to do so

User · Answer

In C  20 you ll be able to use std  format to do this  unsigned char a   -58  std  cout  lt  lt  std  format  quot   b  quot   a    Output  11000110  In the meantime you can use the  fmt  library  std  format is based on   fmt  also provides the print function that makes this even easier and more efficient  godbolt   unsigned char a   -58  fmt  print  quot   b  quot   a    Disclaimer  I m the author of  fmt  and C  20 std  format

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Is there a standard way in C   to show the binary representation in memory of a number          No  There s no std  bin  like std  hex or std  dec  but it s not hard to output a number binary yourself    You output the left-most bit by masking all the others  left-shift  and repeat that for all the bits you have     The number of bits in a type is sizeof T    CHAR BIT

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Similar to what is already posted  just using bit-shift and mask to get the bit  usable for any type  being a template  only not sure if there is a standard way to get number of bits in 1 byte  I used 8 here     include lt iostream gt   include  lt climits gt   template lt typename T gt  void printBin const T amp  t       size t nBytes sizeof T       char  rawPtr  char    amp t        for size t byte 0  byte lt nBytes  byte             for size t bit 0  bit lt CHAR BIT  bit                 std  cout lt  lt    rawPtr byte   gt  gt bit  amp 1                       std  cout lt  lt std  endl      int main void       for int i 0  i lt 50  i             std  cout lt  lt i lt  lt               printBin i

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Using old C   version  you can use this snippet    template lt typename T gt  string toBinary const T amp  t      string s         int n   sizeof T  8    for int i n-1  i gt  0  i--          s     t  amp   1  lt  lt  i    1   0         return s     int main       char a  b     short c    a   -58    c   -315     b   a  gt  gt  3     cout  lt  lt   a      lt  lt  a  lt  lt      gt     lt  lt  toBinary a   lt  lt  endl    cout  lt  lt   b      lt  lt  b  lt  lt      gt     lt  lt  toBinary b   lt  lt  endl    cout  lt  lt   c      lt  lt  c  lt  lt      gt     lt  lt  toBinary c   lt  lt  endl     a     gt  11000110 b     gt  11111000 c   -315   gt  1111111011000101

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Using the std  bitset answers and convenience templates    include  lt iostream gt   include  lt bitset gt   include  lt climits gt   template lt typename T gt  struct BinaryForm       BinaryForm const T amp  v     bs v         const std  bitset lt sizeof T  CHAR BIT gt   bs      template lt typename T gt  inline std  ostream amp  operator lt  lt  std  ostream amp  os  const BinaryForm lt T gt  bf        return os  lt  lt  bf  bs       Using it like this   auto c    A   std  cout  lt  lt   c     lt  lt  c  lt  lt    binary     lt  lt  BinaryForm c   lt  lt  std  endl  unsigned x   1234  std  cout  lt  lt   x     lt  lt  x  lt  lt    binary     lt  lt  BinaryForm x   lt  lt  std  endl  int64 t z   -1024    std  cout  lt  lt   z     lt  lt    lt  lt    binary     lt  lt  BinaryForm z   lt  lt  std  endl    Generates output   c  A binary  01000001 x  1234 binary  00000000000000000000010011010010 z  -1024 binary  1111111111111111111111111111111111111111111111111111110000000000

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Here is the true way to get binary representation of a number   unsigned int i     unsigned int    amp x

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include  lt iostream gt    include  lt cmath gt           in order to use pow   function using namespace std    string show binary unsigned int u  int num of bits    int main          cout  lt  lt  show binary 128  8   lt  lt  endl       should print 10000000   cout  lt  lt  show binary 128  5   lt  lt  endl       should print 00000   cout  lt  lt  show binary 128  10   lt  lt  endl      should print 0010000000    return 0      string show binary unsigned int u  int num of bits        string a          int t   pow 2  num of bits        t is the max number that can be represented    for t  t gt 0  t   t 2               t iterates through powers of 2       if u  gt   t                     check if u can be represented by current value of t           u -  t            a     1                    if so  add a 1               else             a     0                    if not  add a 0            return a                          returns string

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If you want to display the bit representation of any object  not just an integer  remember to reinterpret as a char array first  then you can print the contents of that array  as hex  or even as binary  via bitset     include  lt iostream gt   include  lt bitset gt   include  lt climits gt   template lt typename T gt  void show binrep const T amp  a        const char  beg   reinterpret cast lt const char  gt   amp a       const char  end   beg   sizeof a       while beg    end          std  cout  lt  lt  std  bitset lt CHAR BIT gt   beg     lt  lt           std  cout  lt  lt    n     int main         char a  b      short c      a   -58      c   -315      b   a  gt  gt  3      show binrep a       show binrep b       show binrep c       float f   3 14      show binrep f       Note that most common systems are little-endian  so the output of show binrep c  is not the 1111111 011000101 you expect  because that s not how it s stored in memory  If you re looking for value representation in binary  then a simple cout  lt  lt  bitset lt 16 gt  c  works

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Reusable function   template lt typename T gt  static std  string toBinaryString const T amp  x        std  stringstream ss      ss  lt  lt  std  bitset lt sizeof T    8 gt  x       return ss str        Usage   int main      uint16 t x 8    std  cout  lt  lt  toBinaryString x       This works with all kind of integers

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Is this what you re looking for   std  cout  lt  lt  std  hex  lt  lt  val  lt  lt  std  endl

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Use on-the-fly conversion to std  bitset  No temporary variables  no loops  no functions  no macros   Live On Coliru   include  lt iostream gt   include  lt bitset gt   int main         int a   -58  b   a gt  gt 3  c   -315       std  cout  lt  lt   a      lt  lt  std  bitset lt 8 gt  a    lt  lt  std  endl      std  cout  lt  lt   b      lt  lt  std  bitset lt 8 gt  b    lt  lt  std  endl      std  cout  lt  lt   c      lt  lt  std  bitset lt 16 gt  c   lt  lt  std  endl      Prints   a   11000110 b   11111000 c   1111111011000101

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The easiest way is probably to create an std  bitset representing the value  then stream that to cout   include  lt bitset gt       char a   -58  std  bitset lt 8 gt  x a   std  cout  lt  lt  x  lt  lt    n    short c   -315  std  bitset lt 16 gt  y c   std  cout  lt  lt  y  lt  lt    n

[c++] How to print (using cout) a number in binary form?

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