Crashing when trying to parse a hex string - c

Question

I have a hex string in the form of "404C49474854" .
I am trying to extract the text string out of it with :
void textFromHexString(char *hex,char *result)
{
for(int k=1;k<strlen(hex);k+=2)
{
char temp[3]={0};
sprintf(temp,"%c%c",hex[k-1],hex[k]);
*result=char((int)strtol(temp, NULL, 16));
result++;
*result ='\0';
print(temp); //**** edit
}
}
I call it from inside another function, with :
void somefunction()
{
// I have p here, which prints "404C49474854"
char text[TEXT_MAX_SIZE]={0};
textFromHexString(p,text);
}
It works, but it works 80% of the time. in some cases it crashes, where :
-incoming hex pointer is : "404C49474854". for sure .
-where the pointer temp get a completely other values that are not even inside hex.
Is there something basically wrong with this method ?
EDIT:
Check where the line that prints inside the loop, it will print this in a very specific situation :
4Hello, world
How temp, that consist of numbers only, gets this string ? (the "Hello world", is just a string I print at the beginning of the program, also temp size is 3)

Answer 1

You can use sscanf() to directly read hexadecimal numbers of a given length, like so:
while(hex[0] && hex[1]) {
int value;
sscanf(hex, "%2x", &value);
printf("%c", value);
hex += 2;
}
printf("\n");

Answer 2

It seems as if most errors were found by the commenters, so here is code that works under the assumption that I guessed right what you want.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
// ALL CHECKS OMMITTED!
void textFromHexString(char *hex, char result[])
{
// work on copy
char *p = result;
// this has more steps than necessary for clarity
for (size_t k = 1; k < strlen(hex); k += 2) {
// normalize input
char first = tolower(hex[k - 1]);
char second = tolower(hex[k]);
// convert hexbyte to decimal number
int f1 = (isdigit(first)) ? first - '0' : (first - 'a') + 10;
int f2 = (isdigit(second)) ? second - '0' : (second - 'a') + 10;
// two byte number from LSB hex to decimal (e.g.: "ab" = 171)
int num = f1 * 16 + f2;
// needs to store min. 3 characters plus NUL
char temp[4] = { 0 };
// sprintf is a bit too much for it but simple
sprintf(temp, "%d", num);
// concatenate temp to the result-string
strcat(p, temp);
// For debugging, I guess, or further work?
printf("%s\n", temp);
}
}
#define TEXT_MAX_SIZE 64
int main()
{
// 0x404C49474854 = 70696391100500
char *p = "404C49474854";
// allocate some scratchspace on the stack
char text[TEXT_MAX_SIZE] = { 0 };
textFromHexString(p, text);
// the function textFromHexString() does it in chunks of two bytes,
// so the result is 647673717284 here
printf("Result: %s\n", text);
exit(EXIT_SUCCESS);
}