How to use boost::hash to get the file content has

问题:

Is it possible to use boost:hash function to generate a file content hash with fixed length like MD5?

Is there a quick solution for this?

If not, what is the simplest way?

回答1:

No, Boost doesn't implement MD5. Use a crypto/hash library for this.

CryptoC++ is nice in my experience.

OpenSSL implements all the popular digests, here's a sample that uses OpenSSL:

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#include <openssl/md5.h>
#include <iostream>
#include <iomanip>

// Print the MD5 sum as hex-digits.
void print_md5_sum(unsigned char* md) {
    for(unsigned i=0; i <MD5_DIGEST_LENGTH; i++) {
        std::cout << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(md[i]);
    }
}

#include <string>
#include <vector>
#include <fstream>

int main(int argc, char *argv[]) {
    using namespace std;
    vector<string> const args(argv+1, argv+argc);

    for (auto& fname : args) {

        MD5_CTX ctx;
        MD5_Init(&ctx);

        ifstream ifs(fname, std::ios::binary);

        char file_buffer[4096];
        while (ifs.read(file_buffer, sizeof(file_buffer)) || ifs.gcount()) {
            MD5_Update(&ctx, file_buffer, ifs.gcount());
        }
        unsigned char digest[MD5_DIGEST_LENGTH] = {};
        MD5_Final(digest, &ctx);

        print_md5_sum(digest);
        std::cout << "\t" << fname << "\n";
    }
}

回答2:

boot has such functionality. At lest now: https://www.boost.org/doc/libs/master/libs/uuid/doc/uuid.html

#include <iostream>
#include <algorithm>
#include <iterator>
#include <boost/uuid/detail/md5.hpp>
#include <boost/algorithm/hex.hpp>

using boost::uuids::detail::md5;

std::string toString(const md5::digest_type &digest)
{
    const auto charDigest = reinterpret_cast<const char *>(&digest);
    std::string result;
    boost::algorithm::hex(charDigest, charDigest + sizeof(md5::digest_type), std::back_inserter(result));
    return result;
}

int main ()
{
    std::string s;

    while(std::getline(std::cin, s)) {
        md5 hash;
        md5::digest_type digest;

        hash.process_bytes(s.data(), s.size());
        hash.get_digest(digest);

        std::cout << "md5(" << s << ") = " << toString(digest) << '\n';
    }

    return 0;
}

Live Example