leveldb

hello_leveldb.cc

// get start from http://leveldb.googlecode.com/svn/trunk/doc/index.html
#include <iostream>
#include <algorithm>
#include <string>
#include "leveldb/db.h"
#include "leveldb/cache.h"
#include "leveldb/options.h"

int main()
{
    leveldb::DB* db;
    leveldb::Options options;
    options.create_if_missing = true; // 如果没有则创建
    options.block_cache = leveldb::NewLRUCache(1000 * 1048576L);  // 1000MB cache

    leveldb::Status status = leveldb::DB::Open(options, "index", &db);

    db->Put(leveldb::WriteOptions(),std::string("key::0:"),std::string("")); // init

    std::string key = "key::0:0";
    std::string value = "value789";

    //leveldb::WriteOptions write_options;
    //write_options.sync = true;
    //if((db->Put(write_options, key, value)).ok())
    if((db->Put(leveldb::WriteOptions(), key, value)).ok())
    {
        std::cout << "put ok" << std::endl;
    }

    std::string value1;
    if(!(db->Get(leveldb::ReadOptions(), key, &value1)).ok())
    {
        std::cerr << "read failed " << std::endl;
    }

    std::cout << "[R] k0:" << key << " v0:" << value1 << std::endl;
    std::string key1 = "key::0:1";
    value1.assign("value of value1");
    if(!(db->Put(leveldb::WriteOptions(), key1, value1)).ok()){
        std::cerr << "sth wrong ?? " << __FILE__<< ":" << std::to_string(__LINE__) << std::endl;
        return -1;
    }    


    leveldb::ReadOptions snap_read_opt;
    snap_read_opt.snapshot = db->GetSnapshot();

    leveldb::Iterator* it = db->NewIterator(snap_read_opt);
    //leveldb::Iterator* it = db->NewIterator(leveldb::ReadOptions());

    // it all
    std::cout << "iterator :: all " << std::endl;
    for (it->SeekToFirst(); it->Valid(); it->Next()) 
    {
        std::cout << it->key().ToString() << ": "  << it->value().ToString() << std::endl;
    }

    // it sth
    std::string key_base("key::0:");
    leveldb::Slice key_vect = key_base;
    std::cout << "iterator :: prefix of  " << key_vect.ToString() << std::endl;
    for (it->Seek(key_vect),it->Next();
    //it->Valid() && .substr(0, key_vect.size()-2) == key_vect.ToString().substr(0, key_vect.size()-2);
    it->Valid() && std::mismatch(key_base.begin(),key_base.end(),it->key().ToString().begin()).first == key_base.end();
    it->Next()) {
        std::cout << it->key().ToString() << "\t"  << it->value().ToString() << std::endl;
    }

    // release snapshot
    delete it;
    db->ReleaseSnapshot(snap_read_opt.snapshot);


    if(!(db->Delete(leveldb::WriteOptions(), key1)).ok()){
        std::cerr << "sth wrong ?? " << __FILE__<< ":" << std::to_string(__LINE__) << std::endl;
        return -1;
    }



    //batch
    //leveldb::WriteBatch batch;
    //batch.Delete(key1);
    //batch.Put(key2, value);
    //db->Write(leveldb::WriteOptions(), &batch);

    delete db;
    delete options.block_cache;
    return 0;
}