在软件开发过程中,经常需要对数据进行压缩和解压缩以节省存储空间或加快数据传输速度。本文将介绍如何使用C++语言,结合bzip2库,实现数据的压缩与解压缩功能。
在众多压缩库中,zlib和libbzip2是两个常见的选择。经过比较,选择了bzip2,因为它在压缩比上表现更好,能够生成更小的备份文件。
为了简化使用,设计了两个类来处理压缩和解压缩。这两个类都继承自一个基础类,该基础类封装了bzip2库的调用。
基础类CBZ2Base定义如下:
class CBZ2Base {
protected:
CBZ2Base(char* pWriteBuffer, unsigned int nWriteBufferSize);
protected:
bz_stream m_Stream;
char* m_pWriteBuffer;
unsigned int m_nWriteBufferSize;
};
这个类包含了一个私有变量m_Stream,用于处理bzip2库的调用。
CBZ2Compress类继承自CBZ2Base,定义如下:
class CBZ2Compress : CBZ2Base {
public:
CBZ2Compress(char* pWriteBuffer, unsigned int nWriteBufferSize, int nBlockSize=9, int nWorkFactor=30);
virtual ~CBZ2Compress();
public:
unsigned int Compress();
protected:
virtual unsigned int OnCompressRead(char* &pBuffer) = 0;
virtual void OnCompressWrite(const char* pBuffer, unsigned int nLength) = 0;
};
这个类包含了两个虚函数OnCompressRead和OnCompressWrite,用于读取和写入数据。用户需要重写这两个函数,以实现自己的数据读取和写入逻辑。
CBZ2Decompress类同样继承自CBZ2Base,定义如下:
class CBZ2Decompress : CBZ2Base {
public:
CBZ2Decompress(char* pWriteBuffer, unsigned int nWriteBufferSize, int nSmall=false);
virtual ~CBZ2Decompress();
public:
unsigned int Decompress();
protected:
virtual unsigned int OnDecompressRead(char* &pBuffer) = 0;
virtual void OnDecompressWrite(const char* pBuffer, unsigned int nLength) = 0;
};
这个类也包含了两个虚函数OnDecompressRead和OnDecompressWrite,用于读取和写入数据。用户同样需要重写这两个函数。
下面是一个简单的示例,展示了如何使用CBZ2Compress类来压缩文件:
class CMyCompression : public CBZ2Compress {
public:
CMyCompression() : CBZ2Compress(m_szWriteBuffer, sizeof(m_szWriteBuffer)) {
// Initialize with our buffer
}
BOOL Start(LPCTSTR szSource, LPCTSTR szTarget) {
BOOL bResult=FALSE;
// Assume failure
if (m_fileSource.Open(szSource, CFile::modeRead)) {
if (m_fileTarget.Open(szTarget, CFile::modeCreate|CFile::modeWrite)) {
bResult = (Compress() > 0); // Function should return packed buffer length
m_fileTarget.Close();
}
m_fileSource.Close();
}
return bResult;
}
protected:
virtual unsigned int OnCompressRead(char* &pBuffer) {
// Read some data from our source file
return m_fileSource.Read(pBuffer=m_szReadBuffer, sizeof(m_szReadBuffer));
}
void OnCompressWrite(const char* pBuffer, unsigned int nLength) {
// Write some data to our target file
m_fileTarget.Write(pBuffer, nLength);
}
private:
CFile m_fileSource, m_fileTarget;
char m_szReadBuffer[4096], m_szWriteBuffer[4096];
};
void main() {
CMyCompression a;
a.Start(_T("test.tmp"), _T("test.bz2"));
}