Btukfyl

So I am trying to make a wrapper function for generating a hash using Cryptop++
I created this test function:

#include <cryptopp/sha.h>

#include <cryptopp/hex.h>

#include <cryptopp/cryptlib.h>



#include <vector>

#include <cstdint>



#include <string>



#include <iostream>



void test2()

{

    CryptoPP::SHA1 hash;

    CryptoPP::byte digest[CryptoPP::SHA1::DIGESTSIZE];



    std::vector<uint8_t> v;

    for (uint32_t i = 0; i < 1000; ++i)

    {

        v.push_back(i % 9);

    }



    hash.CalculateDigest(digest, v.data(), v.size());



    CryptoPP::HexEncoder encoder;



    std::string output;



    encoder.Attach(new CryptoPP::StringSink(output));

    encoder.Put(digest, sizeof(digest));

    encoder.MessageEnd();



    std::cout << output << std::endl;

}

And compiled it with the following clang++ string: clang++ main2.cpp -lcryptopp. However, when I use it in my project where the function is defined like this:

template<typename Hash>

std::string get_hash(std::vector<uint8_t> data)

{

Hash hash;



// Intialise a byte "array" with space enough for the result

CryptoPP::byte digest[Hash::DIGESTSIZE];



// Create hash for the data

hash.CalculateDigest(digest, data.data(), data.size());



CryptoPP::HexEncoder encoder;

// result will hold the hex representation of the hash

std::string result;



// Tell the Hex encoder that result is the destination

// for its operations

encoder.Attach(new CryptoPP::StringSink(result));

encoder.Put(digest, sizeof(digest));

// As we will not put more in the message we end it

encoder.MessageEnd();



return result;

}

And call it like this: hash::get_hash<CryptoPP::SHA1>(pair.pivot); with following compiler command: clang++ -std=c++17 -Wall -Werror -Wextra -pthread -pthread -lpqxx -lpq -lcryptopp examples/sql_index_example/sql_index_example.cpp.1.o -o/home/tools/git/alexandria/build/examples/sql_index_example/sql_index_example -Wl-Bstatic -L. -lalexandria -Wl-Bdynamic

I get a ton of undefined references to Crypto++, such as:

examples/sql_index_example/sql_index_example.cpp.1.o: In function `alexandria::data::hash::GetHash[abi:cxx11](std::vector<unsigned char, std::allocator<unsigned char> >)':

sql_index_example.cpp:(.text+0x197): undefined reference to `CryptoPP::StringSinkTemplate<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >::StringSinkTemplate(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&)'

and I am quite lost as to what actually happens when the simple test works. So hope someone can help.

EDIT:
Already tried:
Undefined reference to symbol, even though the library is linked

clang++ -std=c++17 -Wall -Werror -Wextra -pthread -pthread -lpqxx -lpq -lcryptopp 

examples/sql_index_example/sql_index_example.cpp.1.o -o/home/tools/git/alexandria/

build/examples/sql_index_example/sql_index_example -Wl-Bstatic -L. -lalexandria -Wl-Bdynamic

And:

examples/sql_index_example/sql_index_example.cpp.1.o: In function `alexandria::data::hash::

GetHash[abi:cxx11](std::vector<unsigned char, std::allocator<unsigned char> >)':

sql_index_example.cpp:(.text+0x197): undefined reference to ...

To restate what @HolyBlackCat said, -lcryptopp needs to follow sql_index_example.cpp.o because the sql object file needs stuff from the Crypto++ archive. So the compile and link command should probably look something like this:

clang++ -std=c++17 -Wall -Werror -Wextra -pthread -pthread 

  examples/sql_index_example/sql_index_example.cpp.1.o 

  -o /home/tools/git/.../sql_index_example 

  -lpqxx -lpq -lcryptopp -Wl-Bstatic -L. -lalexandria -Wl-Bdynamic

I would even recommend static linking in this case to avoid (1) the stupid Linux path problems; and (2) the path planting/injection games. So maybe smething like:

clang++ -std=c++17 -Wall -Werror -Wextra -pthread -pthread 

  examples/sql_index_example/sql_index_example.cpp.1.o 

  /usr/local/lib/libcryptopp.a 

  -o /home/tools/git/.../sql_index_example 

  -lpqxx -lpq -Wl-Bstatic -L. -lalexandria -Wl-Bdynamic

Also see Why does the order in which libraries are linked sometimes cause errors in GCC?

You may want to change this signature to take a const reference:

std::string get_hash(const std::vector<uint8_t>& data);

There's no need for deep copies here. A reference or pointer will do. References cannot be NULL so they are a little easier to work with.

Also see When to use const and const reference in function args? How to pass objects to functions in C++? has more modern information, including C++11.

Regarding this:

HexEncoder encoder;

// result will hold the hex representation of the hash

std::string result;

// Tell the Hex encoder that result is the destination

// for its operations

encoder.Attach(new StringSink(result));

You can condense it a bit to:

std::string result;

HexEncoder encoder(new StringSink(result));

Since you are printing to std::cout you could even:

std::string result;

HexEncoder encoder(new FileSink(std::cout));

And if you want to get really slick, you can both print it and return it:

ChannelSwitch channels;

channels.AddRoute(new FileSink(std::cout));

channels.AddRoute(new StringSink(result));



HexEncoder encoder(new Redirector(channels));

Now, when you insert data into encoder, it will be hex encoded and then sent to both std::cout and the std::string.

And regarding:

std::vector<uint8_t> data;

...



HexEncoder encoder;

encoder.Attach(new CryptoPP::StringSink(result));

encoder.Put(digest, sizeof(digest));

// As we will not put more in the message we end it

encoder.MessageEnd();

Crypto++ 8.0 will have a VectorSource and VectorSink. You will be able to:

VectorSource(data, true, new HashFilter(hash, 

    new HexEncoder(new StringSink(result))));

return result;

Also see Pull Request 730.