#include <functional> // std::hash
#include <iostream>
#include <string>
/*
Computes a hash value for a string.
std::hash is the standard C++ hashing facility. It is commonly
used by containers such as std::unordered_map and std::unordered_set.
Important notes:
- The same input produces the same hash value within a given implementation.
- Different strings can produce the same hash value (a collision).
- Hashes are intended for fast lookups, not for security.
- Do not use std::hash for password storage or encryption.
*/
std::size_t hashString(const std::string& text)
{
std::hash<std::string> hasher;
return hasher(text);
}
int main()
{
// The string we want to hash.
const std::string text{"Hello, World!"};
// Compute the hash value.
const std::size_t hashValue = hashString(text);
std::cout << "Original string: " << text << '\n';
std::cout << "Hash value : " << hashValue << '\n';
/*
Example comparison:
Rather than comparing long strings repeatedly, many data
structures first compare hash values because comparing
integers is typically faster.
However, a matching hash does not guarantee that two
strings are equal because collisions are possible.
Therefore, when an exact match is required, compare
the original strings as well.
*/
const std::string anotherText{"Hello, World!"};
if (hashString(text) == hashString(anotherText))
{
std::cout << "Hashes match.\n";
// Verify the actual strings to guard against collisions.
if (text == anotherText) {
std::cout << "Strings are identical.\n";
}
}
}
/*
run:
Original string: Hello, World!
Hash value : 18371290486108036847
Hashes match.
Strings are identical.
*/
