How to convert ascii encoded hash to hex encoded one?

Question

So I am using this hash hashing code to genrate a SHA1 hash. And it the hash function returns a std::string which is ASCII encoded and so the hash takes up 40 bytes of memory. And I need to store the hash in 20 byte(and 40 hex character) with hex encoding. How is it done?

Answer 1

At the end of the final method there is some code which writes the digest array as a hex string.

inline std::string SHA1::final()
{
    ...

    /* Hex std::string */
    std::ostringstream result;
    for (size_t i = 0; i < sizeof(digest) / sizeof(digest[0]); i++)
    {
        result << std::hex << std::setfill('0') << std::setw(8);
        result << digest[i];
    }

    /* Reset for next run */
    reset(digest, buffer, transforms);

    return result.str();
}

To get a binary string instead simply replace this code with binary I/O

inline std::string SHA1::final()
{
    ...

    /* Binary std::string */
    std::ostringstream result;
    result.write(reinterpret_cast<char*>(digest), sizeof digest);

    /* Reset for next run */
    reset(digest, buffer, transforms);

    return result.str();
}

Note, as always when writing multibyte integers in binary, there is a potential endianess issue here.