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

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);

Answer 2

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);
....

Answer 3

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);
}

Answer 4

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.

Answer 5

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';
}

Answer 6

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().