text: // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file. See the AUTHORS file for names of contributors.
  //
  // Slice is a simple structure containing a pointer into some external
  // storage and a size.  The user of a Slice must ensure that the slice
  // is not used after the corresponding external storage has been
  // deallocated.
  //
  // Multiple threads can invoke const methods on a Slice without
  // external synchronization, but if any of the threads may call a
  // non-const method, all threads accessing the same Slice must use
  // external synchronization.
  
  #ifndef STORAGE_LEVELDB_INCLUDE_SLICE_H_
  #define STORAGE_LEVELDB_INCLUDE_SLICE_H_
  
  #include <assert.h>
  #include <stddef.h>
  #include <string.h>
  #include <string>
  
  namespace leveldb
  {
  
  class Slice
  {
  public:
      // Create an empty slice.
      Slice() : data_(""), size_(0) { }
  
      // Create a slice that refers to d[0,n-1].
      Slice(const char* d, size_t n) : data_(d), size_(n) { }
  
      // Create a slice that refers to the contents of "s"
      Slice(const std::string& s) : data_(s.data()), size_(s.size()) { }
  
      // Create a slice that refers to s[0,strlen(s)-1]
      Slice(const char* s) : data_(s), size_(strlen(s)) { }
  
      // Return a pointer to the beginning of the referenced data
      const char* data() const
      {
          return data_;
      }
  
      // Return the length (in bytes) of the referenced data
      size_t size() const
      {
          return size_;
      }
  
      // Return true iff the length of the referenced data is zero
      bool empty() const
      {
          return size_ == 0;
      }
  
      // Return the ith byte in the referenced data.
      // REQUIRES: n < size()
      char operator[](size_t n) const
      {
          assert(n < size());
          return data_[n];
      }
  
      // Change this slice to refer to an empty array
      void clear()
      {
          data_ = "";
          size_ = 0;
      }
  
      // Drop the first "n" bytes from this slice.
      void remove_prefix(size_t n)
      {
          assert(n <= size());
          data_ += n;
          size_ -= n;
      }
  
      // Return a string that contains the copy of the referenced data.
      std::string ToString() const
      {
          return std::string(data_, size_);
      }
  
      // Three-way comparison.  Returns value:
      //   <  0 iff "*this" <  "b",
      //   == 0 iff "*this" == "b",
      //   >  0 iff "*this" >  "b"
      int compare(const Slice& b) const;
  
      // Return true iff "x" is a prefix of "*this"
      bool starts_with(const Slice& x) const
      {
          return ((size_ >= x.size_) &&
                  (memcmp(data_, x.data_, x.size_) == 0));
      }
  
  private:
      const char* data_;
      size_t size_;
  
      // Intentionally copyable
  };
  
  inline bool operator==(const Slice& x, const Slice& y)
  {
      return ((x.size() == y.size()) &&
              (memcmp(x.data(), y.data(), x.size()) == 0));
  }
  
  inline bool operator!=(const Slice& x, const Slice& y)
  {
      return !(x == y);
  }
  
  inline int Slice::compare(const Slice& b) const
  {
      const size_t min_len = (size_ < b.size_) ? size_ : b.size_;
      int r = memcmp(data_, b.data_, min_len);
      if (r == 0)
      {
          if (size_ < b.size_) r = -1;
          else if (size_ > b.size_) r = +1;
      }
      return r;
  }
  
  }  // namespace leveldb
  
  
  #endif  // STORAGE_LEVELDB_INCLUDE_SLICE_H_
  