C++ Status::IsNotFound方法代码示例

        /// Cook a cookie for use
        ///
        /// \param result  ref to memory cell that receives cookie if status is
        ///                success
        ///
        /// \note this call should be a pretty rare because it actually does
        ///       lookup for an entry in database
        Status cook(const Slice &name, Cookie &cookie)
        {
            Status s;
            assert( !name.empty() );

            std::string v;
            s = meta.Get(name, v);
            if (s.ok())
            {
                if (Cookie::corrupted(v))
                { return Status::Corruption("Invalid sandwich mapping entry"); }
                cookie = v;
                return s;
            }
            else if (s.IsNotFound())
            {
                Cookie nextCookie;
                s = seq.Next(nextCookie);
                if (s.ok() && nextCookie == 0) s = seq.Next(nextCookie); // skip meta part
                if (s.ok()) s = meta.Put(name, nextCookie);
                if (s.ok()) cookie = nextCookie;
                return s;
            }
            else
            { return s; }
        }

char* leveldb_get(
    leveldb_t* db,
    const leveldb_readoptions_t* options,
    const char* key, size_t keylen,
    size_t* vallen,
    char** errptr) {
  char* result = NULL;
  std::string tmp;
  Status s = db->rep->Get(options->rep, Slice(key, keylen), &tmp);
  if (s.ok()) {
    *vallen = tmp.size();
    result = CopyString(tmp);
  } else {
    *vallen = 0;
    if (!s.IsNotFound()) {
      SaveError(errptr, s);
    }
  }
  return result;
}

int main() {
  // open DB
  Options options;
  TransactionDBOptions txn_db_options;
  options.create_if_missing = true;
  TransactionDB* txn_db;

  Status s = TransactionDB::Open(options, txn_db_options, kDBPath, &txn_db);
  assert(s.ok());

  WriteOptions write_options;
  ReadOptions read_options;
  TransactionOptions txn_options;
  std::string value;

  ////////////////////////////////////////////////////////
  //
  // Simple Transaction Example ("Read Committed")
  //
  ////////////////////////////////////////////////////////

  // Start a transaction
  Transaction* txn = txn_db->BeginTransaction(write_options);
  assert(txn);

  // Read a key in this transaction
  s = txn->Get(read_options, "abc", &value);
  assert(s.IsNotFound());

  // Write a key in this transaction
  s = txn->Put("abc", "def");
  assert(s.ok());

  // Read a key OUTSIDE this transaction. Does not affect txn.
  s = txn_db->Get(read_options, "abc", &value);

  // Write a key OUTSIDE of this transaction.
  // Does not affect txn since this is an unrelated key.  If we wrote key 'abc'
  // here, the transaction would fail to commit.
  s = txn_db->Put(write_options, "xyz", "zzz");

  // Commit transaction
  s = txn->Commit();
  assert(s.ok());
  delete txn;

  ////////////////////////////////////////////////////////
  //
  // "Repeatable Read" (Snapshot Isolation) Example
  //   -- Using a single Snapshot
  //
  ////////////////////////////////////////////////////////

  // Set a snapshot at start of transaction by setting set_snapshot=true
  txn_options.set_snapshot = true;
  txn = txn_db->BeginTransaction(write_options, txn_options);

  const Snapshot* snapshot = txn->GetSnapshot();

  // Write a key OUTSIDE of transaction
  s = txn_db->Put(write_options, "abc", "xyz");
  assert(s.ok());

  // Attempt to read a key using the snapshot.  This will fail since
  // the previous write outside this txn conflicts with this read.
  read_options.snapshot = snapshot;
  s = txn->GetForUpdate(read_options, "abc", &value);
  assert(s.IsBusy());

  txn->Rollback();

  delete txn;
  // Clear snapshot from read options since it is no longer valid
  read_options.snapshot = nullptr;
  snapshot = nullptr;

  ////////////////////////////////////////////////////////
  //
  // "Read Committed" (Monotonic Atomic Views) Example
  //   --Using multiple Snapshots
  //
  ////////////////////////////////////////////////////////

  // In this example, we set the snapshot multiple times.  This is probably
  // only necessary if you have very strict isolation requirements to
  // implement.

  // Set a snapshot at start of transaction
  txn_options.set_snapshot = true;
  txn = txn_db->BeginTransaction(write_options, txn_options);

  // Do some reads and writes to key "x"
  read_options.snapshot = txn_db->GetSnapshot();
  s = txn->Get(read_options, "x", &value);
  txn->Put("x", "x");

  // Do a write outside of the transaction to key "y"
  s = txn_db->Put(write_options, "y", "y");

  // Set a new snapshot in the transaction
//.........这里部分代码省略.........