如何将一个 内存 模拟成一个C++流,

如何将一个 内存 模拟成一个C++流,
把一个内存new出来后,在这段内存上面建立一个 C++ 的istream类.以后所有的操作都可以对这个istream类进行.
这样做有很多好处,比如,你的资源分析器可以接受一个istream指针,这个istream可能是一个fstream.也可能是你从zip文件中解出到内存后，从内存构造的一个istream.

具体做法是,从basic_streambuf里派生一个类,
这里只介绍一个简单的支持输出的streambuf.如果谁完善了它,或者实现了一个支持各种特性,输入输出,block buffer等功能的时候,麻烦也告诉我一下.不胜感激.

#ifndef __MEM_STREAM_BUFFER_H__<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

#define __MEM_STREAM_BUFFER_H__

/*

提供 C++ 标准库的扩展。支持从一段内存上建立一个istream类。

作者： 潘李亮 2004 - 10 - 25

Xheartblue 2004-10-25

本代码为免费代码，可以只有使用和修改。

但是你得保留本声明和作者名字。

*/

#include <streambuf>

namespace std

{

template <typename _CharT, typename _CharTrait = char_traits<_CharT> >

class mem_streambuf : public basic_streambuf<_CharT,_CharTrait>

{

public: //类型的定义

typedef _CharT streambuf_type;

typedef _CharT char_type;

typedef int int_type;

typedef typename std::streampos pos_type;

typedef typename std::streamsize off_type;

protected:

size_t m_bufLen;

char_type* m_buffer;

bool m_bIsAllocInner;

public:

//构造函数

mem_streambuf(char_type* buf,size_t len)

{

set_buf(buf,len);

}

mem_streambuf()

{

m_buffer = NULL;

m_bufLen = 0;

m_bIsAllocInner = false;

}

mem_streambuf(size_t len)

{

m_buffer = NULL;

m_bufLen = 0;

m_bIsAllocInner = false;

alloc_buf(len);

_init();

}

~mem_streambuf()

{

dealloc_buf();

}

bool alloc_buf(int len)

{

dealloc_buf();

m_buffer = new char_type[len];

m_bIsAllocInner = true;

m_bufLen = len;

return true;

}

bool set_buf(char_type* buf,size_t len)

{

m_buffer = buf;

m_bufLen = len;

m_bIsAllocInner = false;

_init();

return true;

}

bool dealloc_buf()

{

if(m_bIsAllocInner)

{

delete [] m_buffer;

}

m_buffer = NULL;

m_bufLen = 0;

m_bIsAllocInner = false;

return true;

}

char_type* get_buf()

{

return m_buffer;

}

protected:

void _init()

{

setg(m_buffer,m_buffer,m_buffer+ m_bufLen);

setp(m_buffer,m_buffer,m_buffer+ m_bufLen);

}

};//endl class mem_streambuf;

template <typename _CharT , typename _CharTrait = char_traits<_CharT> >

class basic_imemstream : public basic_istream<_CharT,_CharTrait>

{

public:

typedef mem_streambuf<_CharT,_CharTrait> stream_type;

typedef _CharT char_type;

protected:

stream_type m_buffer;

public:

basic_imemstream(stream_type* buf): basic_istream<_CharT,_CharTrait>(buf)

{

}

basic_imemstream(char_type* buf,size_t len)

:m_buffer(buf,len),basic_istream<_CharT,_CharTrait>(&m_buffer)

{

}

basic_imemstream():m_buffer(),basic_istream<_CharT,_CharTrait>(&m_buffer)

{

}

basic_imemstream(int len)

:m_buffer(len),basic_istream<_CharT,_CharTrait>(&m_buffer)

{

}

void set_buf(char_type* buf,int len)

{

m_buffer.set_buf(buf,len);

}

char_type* get_buf()

{

return m_buffer.get_buf();

}

basic_streambuf<_CharT,_CharTrait>* rdbuf()

{

return &m_buffer;

}

void rdbuf(basic_streambuf<_CharT,_CharTrait>* buf)

{

m_buffer = buf;

}

};

template <typename _CharT , typename _CharTrait = char_traits<_CharT> >

class basic_omemstream : public basic_ostream<_CharT,_CharTrait>

{

public:

typedef mem_streambuf<_CharT,_CharTrait> stream_type;

typedef _CharT char_type;

protected:

stream_type m_buffer;

public:

basic_omemstream(stream_type* buf): basic_ostream<_CharT,_CharTrait>(buf)

{

}

basic_omemstream(char_type* buf,size_t len)

:m_buffer(buf,len),basic_ostream<_CharT,_CharTrait>(&m_buffer)

{

}

basic_omemstream():m_buffer(),basic_ostream<_CharT,_CharTrait>(&m_buffer)

{

}

basic_omemstream(int len)

:m_buffer(len),basic_ostream<_CharT,_CharTrait>(&m_buffer)

{

}

void set_buf(char_type* buf,int len)

{

m_buffer.set_buf(buf,len);

}

char_type* get_buf()

{

return m_buffer.get_buf();

}

basic_streambuf<_CharT,_CharTrait>* rdbuf()

{

return &m_buffer;

}

void rdbuf(basic_streambuf<_CharT,_CharTrait>* buf)

{

m_buffer = buf;

}

};

template <typename _CharT , typename _CharTrait = char_traits<_CharT> >

class basic_memstream : public basic_ostream<_CharT,_CharTrait>,public basic_istream<_CharT,_CharTrait>

{

public:

typedef mem_streambuf<_CharT,_CharTrait> stream_type;

typedef _CharT char_type;

protected:

stream_type m_buffer;

public:

basic_memstream(stream_type* buf)

: basic_ostream<_CharT,_CharTrait>(buf),

basic_istream<_CharT,_CharTrait>(buf)

{

}

basic_memstream(char_type* buf,size_t len)

:m_buffer(buf,len),

basic_ostream<_CharT,_CharTrait>(&m_buffer),

basic_istream<_CharT,_CharTrait>(&m_buffer)

{

}

basic_memstream()

:m_buffer(),

basic_ostream<_CharT,_CharTrait>(&m_buffer),

basic_istream<_CharT,_CharTrait>(&m_buffer)

{

}

basic_memstream(int len)

:m_buffer(len),

basic_istream<_CharT,_CharTrait>(&m_buffer),

basic_ostream<_CharT,_CharTrait>(&m_buffer)

{

}

void set_buf(char_type* buf,int len)

{

m_buffer.set_buf(buf,len);

}

char_type* get_buf()

{

return m_buffer.get_buf();

}

basic_streambuf<_CharT,_CharTrait>* rdbuf()

{

return &m_buffer;

}

void rdbuf(basic_streambuf<_CharT,_CharTrait>* buf)

{

m_buffer = buf;

}

};

typedef basic_imemstream<char> imemstream;

typedef basic_imemstream<wchar_t> wimemstream;

typedef basic_omemstream<char> omemstream;

typedef basic_omemstream<wchar_t> womemstream;

typedef basic_memstream<char> memstream;

typedef basic_memstream<wchar_t> wmemstream;

}

#endif