Hex to ascii string conversion

Question

i have an hex string and want it to be converted to ascii string in C. How can i accomplish this??

Answer 1

strtol() is your friend here. The third parameter is the numerical base that you are converting.

Example:

#include <stdio.h>      /* printf */
#include <stdlib.h>     /* strtol */

int main(int argc, char **argv)
{
    long int num  = 0;
    long int num2 =0;
    char * str. = "f00d";
    char * str2 = "0xf00d";

    num = strtol( str, 0, 16);  //converts hexadecimal string to long.
    num2 = strtol( str2, 0, 0); //conversion depends on the string passed in, 0x... Is hex, 0... Is octal and everything else is decimal.

    printf( "%ld\n", num);
    printf( "%ld\n", num);
}

Answer 2

you need to take 2 (hex) chars at the same time... then calculate the int value and after that make the char conversion like...

char d = (char)intValue;

do this for every 2chars in the hex string

this works if the string chars are only 0-9A-F:

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

int hex_to_int(char c){
        int first = c / 16 - 3;
        int second = c % 16;
        int result = first*10 + second;
        if(result > 9) result--;
        return result;
}

int hex_to_ascii(char c, char d){
        int high = hex_to_int(c) * 16;
        int low = hex_to_int(d);
        return high+low;
}

int main(){
        const char* st = "48656C6C6F3B";
        int length = strlen(st);
        int i;
        char buf = 0;
        for(i = 0; i < length; i++){
                if(i % 2 != 0){
                        printf("%c", hex_to_ascii(buf, st[i]));
                }else{
                        buf = st[i];
                }
        }
}

Answer 3

Few characters like alphabets i-o couldn't be converted into respective ASCII chars . like in string '6631653064316f30723161' corresponds to fedora . but it gives fedra

Just modify hex_to_int() function a little and it will work for all characters. modified function is

int hex_to_int(char c)
{
    if (c >= 97)
        c = c - 32;
    int first = c / 16 - 3;
    int second = c % 16;
    int result = first * 10 + second;
    if (result > 9) result--;
    return result;
}

Now try it will work for all characters.