Converting an int to a 2 byte hex value in C

Question

I need to convert an int to a 2 byte hex value to store in a char array, in C. How can I do this?

Answer 1

Here's a crude way of doing it. If we can't trust the encoding of ascii values to be consecutive, we just create a mapping of hex values in char. Probably can be optimized, tidied up, and made prettier. Also assumes we only look at capture the last 32bits == 4 hex chars.

#include <stdlib.h>
#include <stdio.h>

#define BUFLEN 5

int main(int argc, char* argv[])
{
  int n, i, cn;
  char c, buf[5];
  char hexmap[17] = {'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F','.'};

  for(i=0;i<BUFLEN;i++)
    buf[i]=0;

  if(argc<2)
  {
    printf("usage: %s <int>\n", argv[0]);
    return 1;
  }
  n = atoi(argv[1]);
  i = 0;
  printf("n: %d\n", n);

  for(i=0; i<4; i++)
  {
    cn = (n>>4*i) & 0xF;
    c  = (cn>15) ? hexmap[16] : hexmap[cn];
    printf("cn: %d, c: %c\n", cn, c);

    buf[3-i] = (cn>15) ? hexmap[16] : hexmap[cn];
  }
  buf[4] = '\0'; // null terminate it

  printf("buf: %s\n", buf);
  return 0;
}

Answer 2

Assuming int to be 32 bits;

easiest way: just use sprintf()

int intval = /*your value*/
char hexval[5];
sprintf(hexval,"%0x",intval);

Now use hexval[0] thru hexval[3]; if you want to use it as a null-terminated string then add hexval[4]=0;

Answer 3

Using Vicky's answer above

typedef unsigned    long    ulong;
typedef unsigned    char    uchar;

#define TO_HEX(i)   (i <= 9 ? '0' + i : 'A' - 10 + i)
#define max_strhex  (sizeof(ulong)*2)

public uchar
*mStrhex(uchar *p, ulong w, ulong n)
{
    ulong i = 0xF;                                  // index
    ulong mask  = i << (((sizeof(ulong)*2)-1)*4);   // max mask (32 bit ulong mask = 0xF0000000, 16 bit ulong mask = 0xF000)
    ulong shift = (w*4);                            // set up shift to isolate the highest nibble
    if(!w || w > max_strhex)                        // no bold params
        return p;                                   // do nothing for the rebel
    mask  = mask >> (max_strhex-w)*4;               // setup mask to extract hex nibbles
    for(i = 0; i < w; i++){                         // loop and add w nibbles
        shift = shift - 4;                          // hint: start mask for four bit hex is 0xF000, shift is 32, mask >> 32 is 0x0000, mask >> 28 is 0x000F.
        *p++ = TO_HEX(((n & mask) >> shift));       // isolate digit and make hex
        mask = mask >> 4;                           //
        *p = '\0';                                  // be nice to silly people
    }                                               //
    return p;                                       // point to null, allow concatenation
}