// http://tinodidriksen.com/2010/01/31/snippet-convert-hex-to-text/
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main() {
    char buf[] = "54657374";
    size_t len = strlen(buf);

    if (len & 1) {
        printf("Cannot take hex from odd length string.\n");
        exit(1);
    }

    char *result = (char*)malloc(len/2 + 1);
    memset(result, 0, len/2 + 1);
    for (size_t i = 0 ; i < len/2 ; ++i) {
        char tmp[3] = {buf[i*2], buf[i*2+1], 0};
        result[i] = (char)strtol(tmp, NULL, 16);
    }

    printf("%s converted to %s\n", buf, result);
    free(result);

    return 0;
}