一种读取文件的方式

每次读取文件1<<15个字节存在一个数组里面 然后调用子类的GetByte()获得一个字节 GetWord()获得双字节 即一个字

class RBaseStream  { public:     RBaseStream();     virtual ~RBaseStream();     virtual bool Open(const char * filename);     virtual void Close();     void         SetBlockSize(int block_size,int ubGetSize=4);     bool         IsOpen();     void         SetPos(int pos);     int          GetPos();     void         Skip(int bytes);     jmp_buf&    JumBuf(); protected:     jmp_buf        m_jmp_buf;     unsigned char* m_start;     unsigned char* m_end;     unsigned char* m_current;     FILE*          m_file;     int            m_unGetsize;     int            m_block_size;     int            m_block_pos;     bool           m_jmp_set;     bool           m_is_opened;     virtual void   ReadBlock();     virtual void   Release();     virtual void   Allocate(); };

 

RBaseStream::RBaseStream() {     m_start=m_end=m_current=0;     m_file=0;     m_block_size=1<<15;     m_unGetsize=4;     m_is_opened=false;     m_jmp_set=false; } void RBaseStream::Allocate() {     if(!m_start)     {         m_start=new unsigned char[m_block_size+m_unGetsize];         m_start+=m_unGetsize;     }     m_end = m_start + m_block_size;     m_current = m_end; } void RBaseStream::ReadBlock() {     unsigned int readed; //    assert( m_file != 0 );     if(m_start)     {         memcpy(m_start - m_unGetsize, m_end - m_unGetsize, m_unGetsize);     }     SetPos( GetPos() );     fseek(m_file , m_block_pos , SEEK_SET);     readed=fread( m_start, 1, m_block_size, m_file );     m_end = m_start + readed;     m_current   -= m_block_size;     m_block_pos += m_block_size;     if(readed == 0 || m_current >= m_end)     {         if( m_jmp_set)             longjmp( m_jmp_buf, -123);     } } bool RBaseStream::Open( const char * filename ) {     Close();     Allocate();     m_file=fopen( filename, "rb" );     if( m_file )     {         m_is_opened = true;         SetPos(0);     }     return m_file != 0; } void RBaseStream::Close() {     if(m_file)     {         fclose(m_file);         m_file = 0;     }     m_is_opened = false; } void RBaseStream::Release() {     if( m_start )     {         delete [](m_start - m_unGetsize);     }     m_start = m_end = m_current = 0; } void RBaseStream::SetBlockSize(int block_size, int unGetsize) {     if( m_start && block_size == m_block_size && unGetsize == m_unGetsize ) return;     Release();     m_block_size = block_size;     m_unGetsize = unGetsize;     Allocate(); } void RBaseStream::SetPos(int pos) {     int offset = pos & (m_block_size - 1);  //经典必看 防止pos数据溢出     int block_pos = pos - offset;     if( m_current < m_end && block_pos == m_block_pos - m_block_size )     {         m_current = m_start + offset;     }     else     {         m_block_pos = block_pos;         m_current = m_start + m_block_size + offset;     } } int RBaseStream::GetPos() {     return m_block_pos - m_block_size + (int)(m_current - m_start); } void RBaseStream::Skip(int bytes) {     m_current += bytes; } jmp_buf& RBaseStream::JumBuf() {     m_jmp_set=true;     return m_jmp_buf; } RBaseStream::~RBaseStream() { }

 

class RLByteStream : public RBaseStream  { public:     int GetWord();     int GetByte();     virtual ~RLByteStream(); };

 

RLByteStream::~RLByteStream() { } int RLByteStream::GetByte() {     unsigned char *current = m_current;     int val;     if( m_current>=m_end)     {         ReadBlock();         current=m_current;     }     val = *( (unsigned char *)current);     m_current = current + 1;     return val; } int RLByteStream::GetWord() {     unsigned char *current=m_current;     int val;     if(current+1 < m_end)     {         val = current[0] + (current[1] << 8);         m_current = current + 2;     }     else     {         val = GetByte();         val|= GetByte() << 8;     }     return val; }