C int to byte array

Question

I have this method in my java code which returns byte array for given int   private static byte   intToBytes int paramInt         byte   arrayOfByte   new byte 4        ByteBuffer localByteBuffer   ByteBuffer allocate 4        localByteBuffer putInt paramInt        for  int i   0  i  lt  4  i             arrayOfByte  3 - i     localByteBuffer array   i        return arrayOfByte      Can someone give me tip how can i convert that method to C

User · Answer

return   byte 0  lt  lt 24   byte 1  lt  lt 16   byte 2  lt  lt 8   byte 3        D

User · Answer

You can get individual bytes with anding and shifting operations   byte1    nint  amp  0x000000ff byte2    nint  amp  0x0000ff00   gt  gt  8 byte3    nint  amp  0x00ff0000   gt  gt  16 byte4    nint  amp  0xff000000   gt  gt  24

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You don t need a whole function for this  a simple cast will suffice   int x  static cast lt char  gt  static cast lt void  gt   amp x      Any object in C   can be reinterpreted as an array of bytes   If you want to actually make a copy of the bytes into a separate array  you can use std  copy   int x  char bytes sizeof x   std  copy static cast lt const char  gt  static cast lt const void  gt   amp x              static cast lt const char  gt  static cast lt const void  gt   amp x     sizeof x            bytes     Neither of these methods takes byte ordering into account  but since you can reinterpret the int as an array of bytes  it is trivial to perform any necessary modifications yourself

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I know this question already has answers but I will give my solution to this problem  I am using template function and integer constraint on it   Here is my solution    include  lt type traits gt   include  lt vector gt   template  lt typename T            typename std  enable if lt std  is arithmetic lt T gt   value gt   type    nullptr gt  std  vector lt uint8 t gt  splitValueToBytes T const amp  value        std  vector lt uint8 t gt  bytes       for  size t i   0  i  lt  sizeof value   i                  uint8 t byte   value  gt  gt   i   8           bytes insert bytes begin    byte              return bytes

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Another useful way of doing it that I use is unions   union byteint       byte b sizeof int       int i     byteint bi  bi i   1337  for int i   0  i lt 4 i        destination i    bi b i     This will make it so that the byte array and the integer will  overlap   share the same memory    this can be done with all kinds of types  as long as the byte array is the same size as the type  else one of the fields will not be influenced by the other    And having them as one object is also just convenient when you have to switch between integer manipulation and byte manipulation copying

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Int to byte and vice versa      unsigned char bytes 4   unsigned long n   1024   bytes 0     n  gt  gt  24   amp  0xFF  bytes 1     n  gt  gt  16   amp  0xFF  bytes 2     n  gt  gt  8   amp  0xFF  bytes 3    n  amp  0xFF   printf   x  x  x  x n   bytes 0   bytes 1   bytes 2   bytes 3      int num   0  for int i   0  i  lt  4  i        num  lt  lt   8   num    bytes i        printf  number  d  num

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I hope mine helps  template  lt typename t int gt  std  array lt uint8 t  sizeof  t int  gt  int2array t int p value        static const uint8 t  size of  static cast lt uint8 t gt  sizeof  t int         typedef std  array lt uint8 t   size of gt  buffer      static const std  array lt uint8 t  8 gt   shifters    8 0  8 1  8 2  8 3  8 4  8 5  8 6  8 7        buffer  res      for  uint8 t  i 0   i  lt   size of     i             res  i    static cast lt uint8 t gt   p value  gt  gt   shifters  i               return  res

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std  vector lt unsigned char gt  intToBytes int value        std  vector lt unsigned char gt  result      result push back value  gt  gt  24       result push back value  gt  gt  16       result push back value  gt  gt   8       result push back value             return result

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Using std  vector lt unsigned char gt     include  lt vector gt  using namespace std   vector lt unsigned char gt  intToBytes int paramInt         vector lt unsigned char gt  arrayOfByte 4        for  int i   0  i  lt  4  i             arrayOfByte 3 - i     paramInt  gt  gt   i   8         return arrayOfByte

User · Answer

An int  or any other data type for that matter  is already stored as bytes in memory  So why not just copy the memory directly   memcpy arrayOfByte   amp x  sizeof x     A simple elegant one liner that will also work with any other data type       If you need the bytes reversed you can use std  reverse  memcpy arrayOfByte   amp x  sizeof x   std  reverse arrayOfByte  arrayOfByte   sizeof x     or better yet  just copy the bytes in reverse to begin with  BYTE  p    BYTE    amp x  std  reverse copy p  p   sizeof x  arrayOfByte       If you don t want to make a copy of the data at all  and just have its byte representation   BYTE  bytes    BYTE    amp x

[c++] C++ int to byte array

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