how do I print an unsigned char as hex in c using ostream

Question

I want to work with unsigned 8-bit variables in C     Either unsigned char or uint8 t do the trick as far as the arithmetic is concerned  which is expected  since AFAIK uint8 t is just an alias for unsigned char  or so the debugger presents it   The problem is that if I print out the variables using ostream in C   it treats it as char   If I have   unsigned char a   0  unsigned char b   0xff  cout  lt  lt   a is    lt  lt  hex  lt  lt  a  lt  lt    b is    lt  lt  hex  lt  lt  b  lt  lt  endl    then the output is   a is     b is 377   instead of   a is 0  b is ff   I tried using uint8 t  but as I mentioned before  that s typedef ed to unsigned char  so it does the same   How can I print my variables correctly   Edit  I do this in many places throughout my code   Is there any way I can do this without casting to int each time I want to print

User · Accepted Answer

I would suggest using the following technique:

struct HexCharStruct
{
  unsigned char c;
  HexCharStruct(unsigned char _c) : c(_c) { }
};

inline std::ostream& operator<<(std::ostream& o, const HexCharStruct& hs)
{
  return (o << std::hex << (int)hs.c);
}

inline HexCharStruct hex(unsigned char _c)
{
  return HexCharStruct(_c);
}

int main()
{
  char a = 131;
  std::cout << hex(a) << std::endl;
}

It's short to write, has the same efficiency as the original solution and it lets you choose to use the "original" character output. And it's type-safe (not using "evil" macros :-))

User · Answer

I d do it like MartinStettner but add an extra parameter for number of digits   inline HexStruct hex long n  int w 2      return HexStruct n  w        Rest of implementation is left as an exercise for the reader   So you have two digits by default but can set four  eight  or whatever if you want to   eg   int main       short a   3142    std cout  lt  lt  hex a 4   lt  lt  std  endl      It may seem like overkill but as Bjarne said   libraries should be easy to use  not easy to write

User · Answer

You can read more about this at http   cpp indi frih net blog 2014 09 tippet-printing-numeric-values-for-chars-and-uint8 t  and http   cpp indi frih net blog 2014 08 code-critique-stack-overflow-posters-cant-print-the-numeric-value-of-a-char    I am only posting this because it has become clear that the author of the above articles does not intend to     The simplest and most correct technique to do print a char as hex is  unsigned char a   0  unsigned char b   0xff  auto flags   cout flags      I only include resetting the ioflags because so                              many answers on this page call functions where                              flags are changed and leave no way to                                return them to the state they were in before                               the function call cout  lt  lt   a is    lt  lt  hex  lt  lt   a  lt  lt    b is    lt  lt   b  lt  lt  endl  cout flags flags     The readers digest version of how this works is that the unary   operator forces a no op type conversion to an int with the correct signedness   So  an unsigned char converts to unsigned int  a signed char converts to int  and a char converts to either unsigned int or int depending on whether char is signed or unsigned on your platform  it comes as a shock to many that char is special and not specified as either signed or unsigned     The only negative of this technique is that it may not be obvious what is happening to a someone that is unfamiliar with it  However  I think that it is better to use the technique that is correct and teach others about it rather than doing something that is incorrect but more immediately clear

User · Answer

I d like to post my re-re-inventing version based on  FredOverflow s  I made the following modifications   fix     Rhs of operator lt  lt  should be of const reference type  In  FredOverflow s code  h x  gt  gt   4 changes output h  which is surprisingly not compatible with standard library  and type T is requared to be copy-constructable  Assume only CHAR BITS is a multiple of 4   FredOverflow s code assumes char is 8-bits  which is not always true  in some implementations on DSPs  particularly  it is not uncommon that char is 16-bits  24-bits  32-bits  etc    improve    Support all other standard library manipulators available for integral types  e g  std  uppercase  Because format output is used in  print byte  standard library manipulators are still available  Add hex sep to print separate bytes  note that in C C   a  byte  is by definition a storage unit with the size of char   Add a template parameter Sep and instantiate  Hex lt T  false gt  and  Hex lt T  true gt  in hex and hex sep respectively  Avoid binary code bloat  Function  print byte is extracted out of operator lt  lt   with a function parameter size  to avoid instantiation for different Size    More on binary code bloat   As mentioned in improvement 3  no matter how extensively hex and hex sep is used  only two copies of  nearly  duplicated function will exits in binary code   print byte lt true gt  and  print byte lt false gt   And you might realized that this duplication can also be eliminated using exactly the same approach  add a function parameter sep  Yes  but if doing so  a runtime if sep  is needed  I want a common library utility which may be used extensively in the program  thus I compromised on the duplication rather than runtime overhead  I achieved this by using compile-time if  C  11 std  conditional  the overhead of function call can hopefully be optimized away by inline   hex print h   namespace Hex   typedef unsigned char Byte   template  lt typename T  bool Sep gt  struct  Hex        Hex const T amp  t    val t             const T amp  val      template  lt typename T  bool Sep gt  std  ostream amp  operator lt  lt  std  ostream amp  os  const  Hex lt T  Sep gt  amp  h      template  lt typename T gt   Hex   Hex lt T  false gt  hex const T amp  x    return Hex   Hex lt T  false gt  x      template  lt typename T gt   Hex   Hex lt T  true gt  hex sep const T amp  x    return Hex   Hex lt T  true gt  x       include  misc tcc    hex print tcc   namespace Hex    struct Put space       static inline void run std  ostream amp  os    os  lt  lt            struct No op       static inline void run std  ostream amp  os          if  CHAR BIT  amp  3     can use C  11 static assert  but no real advantage here  error  hex print utility need CHAR BIT to be a multiple of 4   endif static const size t width   CHAR BIT  gt  gt  2   template  lt bool Sep gt  std  ostream amp   print byte std  ostream amp  os  const void  ptr  const size t size        using namespace std       auto pbyte   reinterpret cast lt const Byte  gt  ptr        os  lt  lt  hex  lt  lt  setfill  0        for  int i   size  --i  gt   0                  os  lt  lt  setw width   lt  lt  static cast lt short gt  pbyte i            conditional lt Sep  Put space  No op gt   type  run os             return os  lt  lt  setfill       lt  lt  dec     template  lt typename T  bool Sep gt  inline std  ostream amp  operator lt  lt  std  ostream amp  os  const  Hex lt T  Sep gt  amp  h        return  print byte lt Sep gt  os   amp h val  sizeof T           test   struct   int x    output    0xdeadbeef   cout  lt  lt  hex sep output   lt  lt  std  uppercase  lt  lt  hex output   lt  lt  endl    output   de ad be ef DEADBEEF

User · Answer

Use   cout  lt  lt   a is    lt  lt  hex  lt  lt   int  a  lt  lt    b is    lt  lt  hex  lt  lt   int  b  lt  lt  endl    And if you want padding with leading zeros then    include  lt iomanip gt      cout  lt  lt   a is    lt  lt  setw 2   lt  lt  setfill  0    lt  lt  hex  lt  lt   int  a      As we are using C-style casts  why not go the whole hog with terminal C   badness and use a macro    define HEX  x      setw 2   lt  lt  setfill  0    lt  lt  hex  lt  lt   int   x     you can then say  cout  lt  lt   a is    lt  lt  HEX  a      Edit  Having said that  MartinStettner s solution is much nicer

User · Answer

I use the following on win32 linux 32 64 bit     include  lt iostream gt   include  lt iomanip gt   template  lt typename T gt  std  string HexToString T uval        std  stringstream ss      ss  lt  lt   0x   lt  lt  std  setw sizeof uval    2   lt  lt  std  setfill  0    lt  lt  std  hex  lt  lt   uval      return ss str

User · Answer

Hm  it seems I re-invented the wheel yesterday    But hey  at least it s a generic wheel this time    chars are printed with two hex digits  shorts with 4 hex digits and so on   template lt typename T gt  struct hex t       T x      template lt typename T gt  hex t lt T gt  hex T x        hex t lt T gt  h    x       return h     template lt typename T gt  std  ostream amp  operator lt  lt  std  ostream amp  os  hex t lt T gt  h        char buffer 2   sizeof T        for  auto i   sizeof buffer  i--                  buffer i     0123456789ABCDEF  h x  amp  15           h x  gt  gt   4            os write buffer  sizeof buffer       return os

User · Answer

I would suggest   std  cout  lt  lt  setbase 16   lt  lt  32    Taken from  http   www cprogramming com tutorial iomanip html

User · Answer

I have used in this way       char strInput      yourchardata   char chHex 2         int nLength   strlen strInput   char  chResut   new char  nLength 2    1   memset chResut  0   nLength 2    1      for  int i   0  i  lt  nLength  i          sprintf chHex    02X   strInput i  amp  0x00FF           memcpy  amp  chResut i 2    chHex  2      printf   n s  chResut   delete chResut  chResut   NULL

User · Answer

In C  20 you ll be able to use std  format to do this  std  cout  lt  lt  std  format  quot a is   x   b is   x  n quot   a  b    Output  a is 0  b is ff  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   fmt  print  quot a is   x   b is   x  n quot   a  b    Disclaimer  I m the author of  fmt  and C  20 std  format

User · Answer

If you re using prefill and signed chars  be careful not to append unwanted  F s  char out character   0xBE   cout  lt  lt  setfill  0    lt  lt  setw 2   lt  lt  hex  lt  lt  unsigned short out character    prints  ffbe   using int instead of short results in ffffffbe  To prevent the unwanted f s you can easily mask them out   char out character   0xBE   cout  lt  lt  setfill  0    lt  lt  setw 2   lt  lt  hex  lt  lt  unsigned short out character   amp  0xFF

User · Answer

This will also work   std  ostream amp  operator lt  lt   std  ostream amp  o  unsigned char c        return o lt  lt  int c     int main         unsigned char a   06      unsigned char b   0xff      std  cout  lt  lt   a is    lt  lt  std  hex  lt  lt  a  lt  lt    b is    lt  lt  std  hex  lt  lt  b  lt  lt  std  endl      return 0

User · Answer

I think we are missing an explanation of how these type conversions work   char is platform dependent signed or unsigned  In x86 char is equivalent to signed char   When an integral type  char  short  int  long  is converted to a larger capacity type  the conversion is made by adding zeros to the left in case of unsigned types and by sign extension for signed ones  Sign extension consists in replicating the most significant  leftmost  bit of the original number to the left till we reach the bit size of the target type   Hence if I am in a signed char by default system and I do this   char a   0xF0     Equivalent to the binary  11110000 std  cout  lt  lt  std  hex  lt  lt  static cast lt int gt  a     We would obtain F   F0 since the leading 1 bit has been extended   If we want to make sure that we only print F0 in any system we would have to make an additional intermediate type cast to an unsigned char so that zeros are added instead and  since they are not significant for a integer with only 8-bits  not printed   char a   0xF0     Equivalent to the binary  11110000 std  cout  lt  lt  std  hex  lt  lt  static cast lt int gt  static cast lt unsigned char gt  a      This produces F0

User · Answer

Well  this works for me   std  cout  lt  lt  std  hex  lt  lt   0xFF  amp  a   lt  lt  std  endl    If you just cast  int  as suggested it might add 1s to the left of a if its most significant bit is 1  So making this binary AND operation guarantees the output will have the left bits filled by 0s and also converts it to unsigned int forcing cout to print it as hex   I hope this helps

User · Answer

You can try the following code   unsigned char a   0  unsigned char b   0xff  cout  lt  lt  hex  lt  lt   a is    lt  lt  int a   lt  lt     b is    lt  lt  int b   lt  lt  endl  cout  lt  lt  hex       lt  lt     a is    lt  lt  setfill  0    lt  lt  setw 2   lt  lt  int a        lt  lt     b is    lt  lt  setfill  0    lt  lt  setw 2   lt  lt  int b        lt  lt  endl  cout  lt  lt  hex  lt  lt  uppercase       lt  lt     a is    lt  lt  setfill  0    lt  lt  setw 2   lt  lt  int a        lt  lt     b is    lt  lt  setfill  0    lt  lt  setw 2   lt  lt  int b        lt  lt  endl    Output   a is 0  b is ff  a is 00  b is ff  a is 00  b is FF

User · Answer

I realize this is an old question  but its also a top Google result in searching for  a solution to a very similar problem I have  which is the desire to implement arbitrary integer to hex string conversions within a template class   My end goal was actually a Gtk  Entry subclass template that would allow editing various integer widths in hex  but that s beside the point   This combines the unary operator  trick with std  make unsigned from  lt type traits gt  to prevent the problem of sign-extending negative int8 t or signed char values that occurs in this answer  Anyway  I believe this is more succinct than any other generic solution  It should work for any signed or unsigned integer types  and throws a compile-time error if you attempt to instantiate the function with any non-integer types   template  lt     typename T    typename   typename std  enable if lt std  is integral lt T gt   value  T gt   type  gt  std  string toHexString const T v       std  ostringstream oss    oss  lt  lt  std  hex  lt  lt     typename std  make unsigned lt T gt   type v     return oss str        Some example usage   int main int argc  char  argv      int16 t val       Prints  ff  instead of  ffffffff   Unlike the other answer using the          operator to extend sizeof char  int types to int unsigned int   std  cout  lt  lt  toHexString int8 t -1    lt  lt  std  endl        Works with any integer type   std  cout  lt  lt  toHexString int16 t 0xCAFE    lt  lt  std  endl        You can use setw and setfill with strings too -OR-       the toHexString could easily have parameters added to do that    std  cout  lt  lt  std  setw 8   lt  lt  std  setfill  0    lt  lt       toHexString int 100    lt  lt  std  endl    return 0      Update  Alternatively  if you don t like the idea of the ostringstream being used  you can combine the templating and unary operator trick with the accepted answer s struct-based solution for the following   Note that here  I modified the template by removing the check for integer types   The make unsigned usage might be enough for compile time type safety guarantees   template  lt typename T gt  struct HexValue      T value    HexValue T  v    value  v          template  lt typename T gt  inline std  ostream amp  operator lt  lt  std  ostream amp  o  const HexValue lt T gt  amp  hs      return o  lt  lt  std  hex  lt  lt     typename std  make unsigned lt T gt   type  hs value      template  lt typename T gt  const HexValue lt T gt  toHex const T val      return HexValue lt T gt  val         Usage  std  cout  lt  lt  toHex int8 t -1    lt  lt  std  endl

User · Answer

I think TrungTN and anon s answer is okay  but MartinStettner s way of implementing the hex   function is not really simple  and too dark  considering hex  lt  lt   int mychar is already a workaround   here is my solution to make   lt  lt   operator easier    include  lt sstream gt   include  lt iomanip gt   string uchar2hex unsigned char inchar      ostringstream oss  ostringstream  out     oss  lt  lt  setw 2   lt  lt  setfill  0    lt  lt  hex  lt  lt   int  inchar     return oss str       int main       unsigned char a   131    std  cout  lt  lt  uchar2hex a   lt  lt  std  endl      It s just not worthy implementing a stream operator  -

[c++] how do I print an unsigned char as hex in c++ using ostream?

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