[Muduo网络库源码分析] (8) base/StringPiece.h_字符串参数传递类型

字符串参数传递类型

实现：StringPiece、StringArg类

功能：实现字符串类型、字符串参数传递类型

知识点：

用途：

可用于字符串传参，和其他字符串处理

代码及分析：

StringPiece.h

// Taken from PCRE pcre_stringpiece.h
//
// Copyright (c) 2005, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// Author: Sanjay Ghemawat
//
// A string like object that points into another piece of memory.
// Useful for providing an interface that allows clients to easily
// pass in either a "const char*" or a "string".
//
// Arghh!  I wish C++ literals were automatically of type "string".

#ifndef MUDUO_BASE_STRINGPIECE_H
#define MUDUO_BASE_STRINGPIECE_H

#include <string.h>
#include <iosfwd>    // for ostream forward-declaration

#include <muduo/base/Types.h>
#ifndef MUDUO_STD_STRING
#include <string>
#endif

namespace muduo {

// For passing C-style string argument to a function.
class StringArg // copyable
{
public:
//构造函数
StringArg(const char* str)
: str_(str)
{     }

//构造函数 string类型
StringArg(const string& str)
: str_(str.c_str())
{ }

#ifndef MUDUO_STD_STRING
StringArg(const std::string& str)
: str_(str.c_str())
{ }
#endif

//返回对应指针
const char* c_str() const { return str_; }

private:
//字符指针
const char* str_;
};

class StringPiece {
private:
//存储指针
const char*   ptr_;
//字符串长度
int           length_;

public:
// We provide non-explicit singleton constructors so users can pass
// in a "const char*" or a "string" wherever a "StringPiece" is
// expected.
//构造函数，初始化
StringPiece()
: ptr_(NULL), length_(0) { }
StringPiece(const char* str)
: ptr_(str), length_(static_cast<int>(strlen(ptr_))) { }
StringPiece(const unsigned char* str)
: ptr_(reinterpret_cast<const char*>(str)),
length_(static_cast<int>(strlen(ptr_))) { }
StringPiece(const string& str)
: ptr_(str.data()), length_(static_cast<int>(str.size())) { }
#ifndef MUDUO_STD_STRING
StringPiece(const std::string& str)
: ptr_(str.data()), length_(static_cast<int>(str.size())) { }
#endif
StringPiece(const char* offset, int len)
: ptr_(offset), length_(len) { }

// data() may return a pointer to a buffer with embedded NULs, and the
// returned buffer may or may not be null terminated.  Therefore it is
// typically a mistake to pass data() to a routine that expects a NUL
// terminated string.  Use "as_string().c_str()" if you really need to do
// this.  Or better yet, change your routine so it does not rely on NUL
// termination.
//返回字符串指针
const char* data() const { return ptr_; }

//返回字符串长度
int size() const { return length_; }

//判断是否为空
bool empty() const { return length_ == 0; }

//起始指针
const char* begin() const { return ptr_; }

//终止指针
const char* end() const { return ptr_ + length_; }

//清空
void clear() { ptr_ = NULL; length_ = 0; }
//重置
void set(const char* buffer, int len) { ptr_ = buffer; length_ = len; }
void set(const char* str) {
ptr_ = str;
length_ = static_cast<int>(strlen(str));
}
void set(const void* buffer, int len) {
ptr_ = reinterpret_cast<const char*>(buffer);
length_ = len;
}

//重载[]运算符
char operator[](int i) const { return ptr_[i]; }
//截掉前n个字符
void remove_prefix(int n) {
ptr_ += n;
length_ -= n;
}
//截掉后n个字符
void remove_suffix(int n) {
length_ -= n;
}

//重载==运算符
bool operator==(const StringPiece& x) const {
return ((length_ == x.length_) &&
(memcmp(ptr_, x.ptr_, length_) == 0));
}
//重载不等于运算符
bool operator!=(const StringPiece& x) const {
return !(*this == x);
}

#define STRINGPIECE_BINARY_PREDICATE(cmp,auxcmp)                             \
bool operator cmp (const StringPiece& x) const {                           \
int r = memcmp(ptr_, x.ptr_, length_ < x.length_ ? length_ : x.length_); \
return ((r auxcmp 0) || ((r == 0) && (length_ cmp x.length_)));          \
}
STRINGPIECE_BINARY_PREDICATE(<,  <);
STRINGPIECE_BINARY_PREDICATE(<=, <);
STRINGPIECE_BINARY_PREDICATE(>=, >);
STRINGPIECE_BINARY_PREDICATE(>,  >);
#undef STRINGPIECE_BINARY_PREDICATE
//比较两个对象是否相等，利用memcmp进行比较
int compare(const StringPiece& x) const {
int r = memcmp(ptr_, x.ptr_, length_ < x.length_ ? length_ : x.length_);
if (r == 0) {
if (length_ < x.length_) r = -1;
else if (length_ > x.length_) r = +1;
}
return r;
}

//以 string 类型返回
string as_string() const {
return string(data(), size());
}

void CopyToString(string* target) const {
target->assign(ptr_, length_);
}

#ifndef MUDUO_STD_STRING
void CopyToStdString(std::string* target) const {
//将string 内容清空，并将ptr_字符串赋值给string
target->assign(ptr_, length_);
}
#endif
//将StringPiece与当前字符串比较是否相同
// Does "this" start with "x"
bool starts_with(const StringPiece& x) const {
return ((length_ >= x.length_) && (memcmp(ptr_, x.ptr_, x.length_) == 0));
}
};

}   // namespace muduo

// ------------------------------------------------------------------
// Functions used to create STL containers that use StringPiece
//  Remember that a StringPiece's lifetime had better be less than
//  that of the underlying string or char*.  If it is not, then you
//  cannot safely store a StringPiece into an STL container
// ------------------------------------------------------------------

#ifdef HAVE_TYPE_TRAITS
// 经过特化的StringPiece
// This makes vector<StringPiece> really fast for some STL implementations
template<> struct __type_traits<muduo::StringPiece> {
typedef __true_type    has_trivial_default_constructor;//有构造函数
typedef __true_type    has_trivial_copy_constructor;   //有复制构造函数
typedef __true_type    has_trivial_assignment_operator;//有赋值函数
typedef __true_type    has_trivial_destructor;         //有析构函数
typedef __true_type    is_POD_type;                    //是C++的内建类型或传统的C结构体类型
};
#endif

// allow StringPiece to be logged
// 重载运算符，以便写日志
std::ostream& operator<<(std::ostream& o, const muduo::StringPiece& piece);

#endif  // MUDUO_BASE_STRINGPIECE_H