Convert Hexadecimal String to Data

Question

I have found a whole lot of different solutions to this problem, but not all of them work, and a lot of them seem somewhat hacky and inefficient. Basically I have a string of hexadecimal data (i.e. "55 AA 41 2A 00 94 55 AA BB BB 00 FF") which I would like to convert to raw data. What is the best way to do this?

UPDATE: Vicky's solution worked great for me, but I changed it to work with hexadecimal strings that don't have spaces in between and changed the style a bit.

int i = 0;
char *hexString = "55AA412A009455AABBBB00FF"
char *hexPtr = hexString;
unsigned int *result = calloc(strlen(hexString)/2 + 1, sizeof *result);

while (sscanf(hexPtr, "%02x", &result[i++])) {
    hexPtr += 2;
    if (hexPtr >= hexString + strlen(hexString)) break;
}

return result;

Could you clarify, shortly, on the few approaches you tried and in what type of context this code should fit? — nielsj
– nielsj, Commented May 18, 2010 at 12:23
(Maybe not the best but the shortest for sure;) possible duplicate of Code golf - hex to (raw) binary conversion — zaf
– zaf, Commented May 18, 2010 at 12:26
zaf, that is exactly what I wanted, sorry I didn't see that before. I guess this would in a way be a duplicate of that. — AriX
– AriX, Commented May 18, 2010 at 14:05
There's no need to cast &result[i++] to (unsigned int *) - it already has that type. Also you do not allocate enough space for result - you need to replace the final , 1) in the calloc call with sizeof *result. — caf
– caf, Commented May 18, 2010 at 22:41

Vicky · Accepted Answer · 2010-05-19 09:50:00Z

2

Is the string always the same length?

If so:

char *buf = "55 AA 41 2A 00 94 55 AA BB BB 00 FF";
sscanf(buf, "%x %x %x [repeat as many times as necessary]", &a, &b, &c [etc]);

If not:

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

int main (int argc, char ** argv)
{
    char *buf = "55 AA 41 2A 00 94 55 AA BB BB 00 FF";
    char *p = buf;
    int i = 0, j;
    unsigned int *result = calloc(strlen(buf)/3 + 1 * sizeof(int), 1);

    if (result)
    {
        while (sscanf(p, "%02x", &result[i++]))
        {
             p += 3;
            if (p > buf + strlen(buf))
            {
             break;
            }
        }

        printf("%s\n", buf);

        for (j = 0; j < i; j++)
        {
            printf("%02X ", result[j]);
        }

        printf("\n");
    }
}

edited May 19, 2010 at 9:50

answered May 18, 2010 at 13:03

Vicky

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1 Comment

caf Over a year ago

The %02x conversion specifier requires a pointer to unsigned int, but you are passing it a pointer to unsigned char. This results in undefined behaviour (in practice, your answer will produce incorrect results on machines that aren't little-endian, and crash on machines with strict alignment requirements).

ablaeul · Accepted Answer · 2010-05-18 13:01:56Z

1

Did you try sscanf or scanf? This function processes hexadecimal values to and returns "raw data".

answered May 18, 2010 at 13:01

ablaeul

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Comments

qrdl · Accepted Answer · 2010-05-18 13:20:04Z

0

#define GETBITS(a) (a < 'A' ? a - '0' : toupper(a) - 'A' + 10)

char *cur;
char data;
for (cur = buffer; *cur; cur++) {
    data = GETBITS(cur[0]) << 4 + GETBITS(cur[1]);
    cur += 2;
    printf("%c", data);
}
printf("\n");

answered May 18, 2010 at 13:20

qrdl

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Comments

moffeltje · Accepted Answer · 2015-07-15 09:24:39Z

0

while(input[i]!='\0'){        
    *(temp++) = ((input[i]>='0' && input[i]<='9')?(input[i]-'0'):(input[i]-'a'+10))*16 +( (input[i+1]>='0' && input[i]<='9')?(input[i+1]-'0'):(input[i+1]-'a'+10));
         i+=2;
}

edited Jul 15, 2015 at 9:24

moffeltje

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answered Jul 15, 2015 at 5:41

Vishwanath Patil

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Comments

ButterCYassine · Accepted Answer · 2022-07-24 01:32:12Z

 /*
  * copyLeft (ButterC) All Right Changed :)
 */
 void _StackOverFlow(void *data) {

    unsigned char *ButterC = (unsigned char *) data;
    size_t ssize ,size = ssize = 0; 

    int i;

    for (i = 0; ButterC[i] != 0; i++)
    {
            if (ButterC[i] != 32)
                    size++;
    }

    unsigned int *resu = (unsigned int *) malloc((size / 2) + 1);


    while (*ButterC != 0 && resu != NULL && ssize < size) 
    {
            if (*ButterC == 32) 
                    ButterC++;
            else {
                    sscanf(ButterC,"%02x",&resu[ssize++]); ButterC += 2;
            }
    }
    // TEST RESULTE TO => (resu) 
    for (i = 0; i < ssize; i++)
    {
            printf("%02X ",resu[i] & 0xff);
    }

    puts(""); // NEWLINE  
}

int _start() {

    char data[] = "FF 00FF           01";
    _StackOverFlow(data);

    
    _exit(0);
}

nudeln · Accepted Answer · 2025-07-03 20:24:20Z

I had a similar problem. I passed a "hex"-argument from python to a c-binary, i.e. 568AD6E4338BD93479C210105CD4198B, like:

subprocess.getoutput("binary.exe 568AD6E4338BD93479C210105CD4198B")

In my binary I wanted the passed argument to be stored in a uint8_t hexarray[16], but instead of char value '5' (raw hex 0x35), I needed actual raw hex value 0x5... and 32 chars make up a 16 sized uint8_t array, thus bit shifting etc..

for (i=0;i<16;i++) {
    if (argv[1][i*2]>0x40)
        hexarray[i] = ((argv[1][i*2] - 0x37) << 4);
    else 
        hexarray[i] = ((argv[1][i*2] - 0x30) << 4);
    if (argv[1][i*2+1]>0x40)
        hexarray[i] = hexarray[i] + (argv[1][i*2+1] - 0x37);
    else 
        hexarray[i] = hexarray[i] + (argv[1][i*2+1] - 0x30);

This would only work for hexstrings with upper chars.

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