Mine

int md_len=5;
char md_value[5]={0x12,0x21,0x34,0x54,0x66};
// double the size
char* base_ptr = new char(md_len * 2);
//
char* chars="0123456789ABCDEF";
int main(int argc, char* argv[])
{
char* dest_ptr=base_ptr;
memset (dest_ptr,0,10);
for(int j = 0; j < md_len; j++) {
*dest_ptr++=chars[(md_value[j]&0xf0)>>4];
*dest_ptr++=chars[(md_value[j]&0xf)];
}
	printf("%s\n",base_ptr);
	return 0;
}