Re: generating sha256 hashes with openssl?
- From: "Littlefield, Tyler" <tyler@xxxxxxxxxxxxx>
- To: <programmingblind@xxxxxxxxxxxxx>
- Date: Sun, 22 Aug 2010 21:35:45 -0600
I seem to have forgotten a line:
While this isn't good coding practice, it's a great example of what I'm
saying...
#include <iostream>
#include <string>
#include <cstring>
int main(void)
{
char* i = new char(10);
memset(i, 0, 10);
strcpy(i, "hello!");
std::string s=i;
delete [] i;
memset(i, 0, 10);
std::cout << s << std::endl;
return 0;
}
In short, we create an array of 10 bytes, fill it with zeros (so the string
is NULL terminated), assign that to a std::string, delete the array and set
the 10 bytes at that address back to zero. If the std::string held a
reference or just the address of that pointer, we wouldn't see the "hello"
being printed, because the memory where the array was was just filled with
zeros. The fact that it is, tells us that std::string's = operator does a
strcpy, or a similar copy operation.
----- Original Message -----
From: "Littlefield, Tyler" <tyler@xxxxxxxxxxxxx>
To: <programmingblind@xxxxxxxxxxxxx>
Sent: Sunday, August 22, 2010 9:30 PM
Subject: Re: generating sha256 hashes with openssl?
#include <iostream>
#include <string>
#include <cstring>
int main(void)
{
char* i = new char(10);
memset(i, 0, 10);
strcpy(i, "hello!");
std::string s=i;
delete [] i;
std::cout << s << std::endl;
return 0;
}
tyler@tangerine:~$ g++ poc.cpp
tyler@tangerine:~$ ./a.out
hello!
tyler@tangerine:~$
so... It -is- copying, as I said earlier.
the std::string manages it's own array, so it can expand and etc. A smart
pointer won't do any good as it's not used after the strcpy, thus deleting
it has no affect here.
Thanks,
Ty
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