.. _examples_initchain:

examples/initchain.cpp
######################

Create a new leveldb blockchain database.

::

    #include <future>
    #include <bitcoin/bitcoin.hpp>
    using namespace bc;

    int main(int argc, char** argv)
    {
        if (argc != 2)
            return 1;
        const std::string dbpath = argv[1];
        // Threadpool context containing 1 thread.
        threadpool pool(1);
        // leveldb_blockchain operations execute in pool's thread.
        leveldb_blockchain chain(pool);
        // Completion handler for starting the leveldb_blockchain.
        // Does nothing.
        auto blockchain_start = [](const std::error_code& ec) {};
        // Start blockchain with a database path.
        chain.start(dbpath, blockchain_start);
        // First block is the genesis block.
        block_type first_block = genesis_block();
        std::promise<std::error_code> ec_promise;
        // Completion handler for import method.
        auto import_finished = 
            [&ec_promise](const std::error_code& ec)
            {
                ec_promise.set_value(ec);
            };
        // Import the genesis block at height 0.
        // Doesn't validate or perform checks on the block.
        chain.import(first_block, 0, import_finished);
        // Wait until std::error_code is set by
        // import_finished completion handler.
        std::error_code ec = ec_promise.get_future().get();
        if (ec)
        {
            log_error() << "Importing genesis block failed: " << ec.message();
            return -1;
        }
        log_info() << "Imported genesis block "
            << hash_block_header(first_block.header);
        // All threadpools stopping in parallel...
        pool.stop();
        // ... Make them all join main thread and wait until they finish.
        pool.join();
        // Now safely close leveldb_blockchain.
        chain.stop();
        return 0;
    }

