levelDB之基础数据结构-Slice

Slice是levelDB中用于操作字符串的数据结构，以字节为单位。

定义与实现

namespace leveldb {class LEVELDB_EXPORT 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)) {}//拷贝函数的定义，默认是浅拷贝Slice(const Slice&) = default;Slice& operator=(const Slice&) = default;// 返回底层的字符数组指针const char* data() const { return data_; }// 返回data的字节数size_t size() const { return size_; }// 返回字符串是否为空bool empty() const { return size_ == 0; }// 重载下标运算符，用于获取第n个字节的字符char operator[](size_t n) const {assert(n < size());return data_[n];}// 清空slicevoid clear() {data_ = "";size_ = 0;}// 移除前n个字节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:// 用于存储实际的字符数据const char* data_;// 字符串占用的字节数size_t size_;
};// 比较两个slice是否相同
inline bool operator==(const Slice& x, const Slice& y) {return ((x.size() == y.size()) &&(memcmp(x.data(), y.data(), x.size()) == 0));
}// 重载 != ,用于比较两个slice不相等
inline bool operator!=(const Slice& x, const Slice& y) { return !(x == y); }// 比较两个字符串的大小
// 按照字典序比较，0 表示相等；1 表示大于b；-1表示小于b
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;
}}