使用7Z开源SDK压缩解压数据(LzmaCompress、LzmaUncompress)

使用开源的7Z SDK中的比较重要的两个函数LzmaCompress、LzmaUncompress压缩和解压数据，这里仅仅是用来处理数据而非7Z文件，可用在网络通信、本地数据保存等需要节省空间的时候，关键是7Z的压缩比一般是最高的，对比ZIP、RAR算法。

首先是去官网下载SDK，解压后使用VC6及以上版本编译C文件夹下lzmaLib工程，生成了一个lzma.dll，体积很小，使用起来也很方便。下面是调用这两个函数来压缩和解压一个小的文件的代码，由于没有加入文件信息，所以不是标准7Z文件（本文主要是压缩数据而非文件）。

使用前需要先把7Z定义的一些常量复制过来，然后就是声明函数指针：

#define SZ_OK 0

#define SZ_ERROR_DATA 1
#define SZ_ERROR_MEM 2
#define SZ_ERROR_CRC 3
#define SZ_ERROR_UNSUPPORTED 4
#define SZ_ERROR_PARAM 5
#define SZ_ERROR_INPUT_EOF 6
#define SZ_ERROR_OUTPUT_EOF 7
#define SZ_ERROR_READ 8
#define SZ_ERROR_WRITE 9
#define SZ_ERROR_PROGRESS 10
#define SZ_ERROR_FAIL 11
#define SZ_ERROR_THREAD 12

#define SZ_ERROR_ARCHIVE 16
#define SZ_ERROR_NO_ARCHIVE 17
//定义压缩函数指针
typedef int (__stdcall *LzmaCompress)(unsigned char *, size_t*, const unsigned char *, size_t, unsigned char *,
									  size_t *, int, unsigned, int, int, int, int, int);
//定义解压函数指针
typedef int (__stdcall *LzmaUncompress)(unsigned char *dest, size_t  *destLen, const unsigned char *src, size_t  *srcLen,
			   const unsigned char *props, size_t propsSize);

HMODULE hModule = LoadLibrary(L"LZMA.dll");
	if ( NULL == hModule )
	{
		cout<<"没有找到LZMA.dll"<<endl;
		return 0;
	}
	LzmaCompress pLzmaCom = (LzmaCompress)GetProcAddress(hModule, "LzmaCompress");
	byte prop[5] = {0};
	size_t nPropSize = 5;
	if ( pLzmaCom )
	{
		FILE* fp = fopen("c:\\1.jpg", "rb");
		if ( NULL != fp )
		{
			fseek(fp, 0, SEEK_END);
			size_t nSrcLen = ftell(fp);
			fseek(fp, 0, SEEK_SET);
			byte* pSrcData = (byte*)malloc(nSrcLen);
			fread(pSrcData, nSrcLen, 1, fp);
			fclose(fp);
			size_t nDesLen = nSrcLen;
			byte* pDesData = (byte*)malloc(nDesLen);
			int nRet = pLzmaCom(pDesData, &nDesLen, pSrcData, nSrcLen, prop, &nPropSize, \
				9, 1<<24, 3, 0, 2, 32, 2);
			if ( SZ_ERROR_OUTPUT_EOF == nRet )
			{//申请内存不足
				free(pDesData);
				nDesLen += nSrcLen;
				pDesData = (byte*)malloc(nDesLen);
				nRet = pLzmaCom(pDesData, &nDesLen, pSrcData, nSrcLen, prop, &nPropSize, \
					9, (1<<24), 3, 0, 2, 32, 2);
			}
			if ( SZ_OK == nRet )
			{//压缩完成
				fp = fopen("c:\\des_7z.dat", "wb+");
				if ( NULL != fp )
				{
					fwrite(pDesData, nDesLen, 1, fp);
					fclose(fp);
				}
			}
			free(pDesData);
			free(pSrcData);
		}
	}
	//解压文件
	LzmaUncompress pLzmaUncom = (LzmaUncompress)GetProcAddress(hModule, "LzmaUncompress");
	if ( pLzmaUncom )
	{
		FILE* fp = fopen("c:\\des_7z.dat", "rb");
		if ( NULL != fp )
		{
			fseek(fp, 0, SEEK_END);
			size_t nSrcLen = ftell(fp);
			fseek(fp, 0, SEEK_SET);
			byte* pSrcData = (byte*)malloc(nSrcLen);
			fread(pSrcData, nSrcLen, 1, fp);
			fclose(fp);
			size_t nDesLen = 1.1*nSrcLen + 16*1024;
			byte* pDesData = (byte*)malloc(nDesLen);
			int nRet = pLzmaUncom(pDesData, &nDesLen, pSrcData, &nSrcLen, prop, nPropSize);
			if ( SZ_ERROR_INPUT_EOF  == nRet )
			{//申请空间不足
				free(pDesData);
				pDesData = (byte*)malloc(nDesLen);
				nRet = pLzmaUncom(pDesData, &nDesLen, pSrcData, &nSrcLen, prop, nPropSize);
			}
			if ( SZ_OK == nRet )
			{//解压完成
				fp = fopen("c:\\out.jpg", "wb+");
				if ( NULL != fp )
				{
					fwrite(pDesData, nDesLen, 1, fp);
					fclose(fp);
				}
			}
			free(pSrcData);
			free(pDesData);
		}
	}
	FreeLibrary(hModule);

涉及到文件读写，内存申请、释放之类的基础就不说了，希望对大家有所帮助。