Convert unsigned integer with hexdecimals to string

Question

I have an _u8 Array with hexadecimals in it, in the form of: A81B6A9D4D2E for example. And I want to turn it into an string in the form of: A8-1B-6A-9D-4D-2E and have it as a string to send it.

#define SL_MAC_ADDR_LEN     UINT8_C(6)
_u8 wlanMacAddressVal[SL_MAC_ADDR_LEN];

I can print it with a Loop as following:

for(int i = 0; i < SL_MAC_ADDR_LEN; i++){
printf(%X, wlanMacAddressVal[i]);
printf("-");
}

But when I try to make a string/chararray and using the strcat Function my results are always weird symbols.

I've tried using sprintf() in the loop, but it always overwrites the last hexadecimals

sprintf(wlanMacString,"%X",(_u8 *)wlanMacAddressVal[i]);

Try using `sprintf()` to make the string. Also, please post valid code - ideally the [Minimal Reproducible Example](https://stackoverflow.com/help/minimal-reproducible-example) that shows the problem. Note, the array does not contain hexadecimals but binary values, which you want to convert to hexadecimal text. — Weather Vane, Jun 18 '19 at 07:20
I've tried sprintf(), but it always overwrites the last characters. so I only get the last hexdecimal. — Nostra, Jun 18 '19 at 07:47
Possible duplicate of [How to convert an Unsigned Character array into a hexadecimal string in C](https://stackoverflow.com/questions/5661101/how-to-convert-an-unsigned-character-array-into-a-hexadecimal-string-in-c) — Scheff's Cat, Jun 18 '19 at 07:47

kiran Biradar · Accepted Answer · 2019-06-18T10:44:23.753

3

Use sprintf with 02x format specifier.

char buf[SL_MAC_ADDR_LEN*3]; //2*number of hex bytes + number of `-` symbols + \0.


char *p = buf;
for (int i=0;i<SL_MAC_ADDR_LEN;i++)
  p += sprintf(p, i ? "-%02hhx":"%02hhx", _u8Array[i]);

Note that you need to advance p to skip number of bytes printed so far in the buffer.

edited Jun 18 '19 at 10:44

answered Jun 18 '19 at 07:50

kiran Biradar

12,700
3
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Simplification: `p += sprintf(p, i ? "-%02x":"%02x", _u8Array[i]);` – chux - Reinstate Monica Jun 18 '19 at 10:28
`SL_MAC_ADDR_LEN*2+SL_MAC_ADDR_LEN+1` is off by 1. `SL_MAC_ADDR_LEN*3` is sufficient. Yet since `_u8` is not certainly _unsigned_, consider `"%02hhx"` or some other limiting code. – chux - Reinstate Monica Jun 18 '19 at 10:38
@chux Taken the suggestion. Thank you :D – kiran Biradar Jun 18 '19 at 10:44

0___________ · Answer 2 · 2019-06-18T11:53:22.157

3

If you are on the resurce limited hardware (for example uC) using sprintf is not a good idea.

static const char digits[]="0123456789ABCDEF";

char *bytetostr(char *buff, const uint8_t val)
{
    buff[0] = digits[val >> 4];
    buff[1] = digits[val & 0x0f];
    buff[2] = 0;
    return buff;
}


char *bytearrtostring(char *buff, const uint8_t *arr, size_t length, const int separator)
{
    char *result = buff;

    while(length)
    {
        bytetostr(buff, *arr++);
        if(--length)
        {
             buff[2] = separator;
             buff += 3;
        }
    }
    buff = 0;

    return result;
}

int main()
{
    uint8_t array[] = {0xa1, 0x45, 0xde, 0x67, 0xff, 0x00};

    char buff[100];

    printf("%s\n", bytearrtostring(buff, array, sizeof(array), '-'));
}

You can experiment yourself https://onlinegdb.com/HJy5KGLyS

https://godbolt.org/z/3bQa1-

edited Jun 18 '19 at 11:53

answered Jun 18 '19 at 07:54

0___________

60,014
4
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1) A `while(length) { ...}` would allow `bytearrtostring(buff, array, 0, '-'));` to perform without UB. 2) `buff = 0;` serves no purpose. I suspect you want to increment `buff` by 2 when `if(--length)` is false and later `*buff = 0;` – chux - Reinstate Monica Jun 18 '19 at 10:34
Aside from various such implementation nit-picks, this solution is superior to sprintf on any system, not just microcontrollers. C was never a high level language., so PC programmers using C should actually learn real programming too, instead of just relying on magic libs. – Lundin Jun 18 '19 at 11:14

Convert unsigned integer with hexdecimals to string

2 Answers2