Converting an int to a 2 byte hex value in C

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

If you're allowed to use library functions:

int x = SOME_INTEGER;
char res[5]; /* two bytes of hex = 4 characters, plus NULL terminator */

if (x <= 0xFFFF)
{
    sprintf(&res[0], "%04x", x);
}

Your integer may contain more than four hex digits worth of data, hence the check first.

If you're not allowed to use library functions, divide it down into nybbles manually:

#define TO_HEX(i) (i <= 9 ? '0' + i : 'A' - 10 + i)

int x = SOME_INTEGER;
char res[5];

if (x <= 0xFFFF)
{
    res[0] = TO_HEX(((x & 0xF000) >> 12));   
    res[1] = TO_HEX(((x & 0x0F00) >> 8));
    res[2] = TO_HEX(((x & 0x00F0) >> 4));
    res[3] = TO_HEX((x & 0x000F));
    res[4] = '\0';
}

Figured out a quick way that I tested out and it works.

int value = 11;

array[0] = value >> 8;
array[1] = value & 0xff;

printf("%x%x", array[0], array[1]);

result is:

000B

which is 11 in hex.

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;

char s[5];  // 4 chars + '\0'
int x = 4660;
sprintf(s, "%04X", x);

You'll probably want to check sprintf() documentation. Be careful that this code is not very safe. If x is larger than 0xFFFF, the final string will have more than 4 characters and won't fit. In order to make it safer, look at snprintf().

Normally I would recommend using the sprintf based solutions recommended by others. But when I wrote a tool that had to convert billions of items to hex, sprintf was too slow. For that application I used a 256 element array, which maps bytes to strings.

This is an incomplete solution for converting 1 byte, don't forget to add bounds checking, and make sure the array is static or global, recreating it for every check would kill performance.

static const char hexvals[][3]= {"00", "01", "02", ... "FD", "FE", "FF"};
const char *byteStr = hexvals[number];

void intToHex(int intnumber, char *txt)
{    
    unsigned char _s4='0';
    char i=4;
    //intnumber=0xffff;

    do {
        i--;
        _s4 = (unsigned char)  ((intnumber >> i*4 ) & 0x000f);
        if(_s4<10)
            _s4=_s4+48;
        else
            _s4=_s4+55;

        *txt++= _s4;    
    } while(i);     
}
...
char text [5]={0,0,0,0,0};
...

intToHex(65534,text);
USART_Write_Text(text);
....

Rather than sprintf, I would recommend using snprintf instead.

#include <stdio.h>

int main()
{
    char output[5];
    snprintf(output,5,"%04x",255);

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

Its a lot safer, and is available in pretty much every compiler.

Perhaps try something like this:

void IntToHex(int value, char* buffer) {
  int a = value&16;
  int b = (value>>4)&16;
  buffer[0] = (a<10)?'0'+a:'A'-(a-10);
  buffer[1] = (b<10)?'0'+b:'A'-(b-10);
}

Most of these answers are great, there's just one thing I'd add: you can use sizeof to safely reserve the correct number of bytes. Each byte can take up to two hex digits (255 -> ff), so it's two characters per byte. In this example I add two characters for the '0x' prefix and one character for the trailing NUL.

int bar; 
// ...
char foo[sizeof(bar) * 2 + 3];
sprintf(foo, "0x%x", bar);

unsigned int hex16 = ((unsigned int) input_int) & 0xFFFF;

input_int is the number you want to convert. hex16 will have the least significant 2 bytes of input_int. If you want to print it to the console, use %x as the format specifier instead of %d and it will be printed in hex format.

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;
}

This function works like a charm.

void WORD2WBYTE(BYTE WBYTE[2], WORD Value) { 
    BYTE tmpByte[2]; 
    // Converts a value from word to word byte ----
    memcpy(tmpByte, (BYTE*) & Value, 2); 
    WBYTE[1] = tmpByte[0]; 
    WBYTE[0] = tmpByte[1]; 
} 

asumming the following:

typedef unsigned char   BYTE; 
typedef unsigned short  WORD;

Example of use:

we want to achieve this:

integer = 92
byte array in hex:
a[0] = 0x00;
a[1] = 0x5c;

unsigned char _byteHex[2];
WORD2WBYTE(_byteHex, 92);

you can use this it is simple and easy to convert

typedef union {
    struct hex{
            unsigned  char a;
            unsigned  char b;

    }hex_da;
    short int dec_val;
}hex2dec;

hex2dec value;
value.dec_val=10;

Now hex value is stored in hex_da structure access it for further use.

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
}

For dynamic fixed length of hex

string makeFixedLengthHex(const int i, const int length)
{
    std::ostringstream ostr;
    std::stringstream stream;
    stream << std::hex << i;
    ostr << std::setfill('0') << std::setw(length) << stream.str();
    return ostr.str();
}

But negative you have to handle it yourself.