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zlib是个著名的开源解压缩库，gzip是一种压缩文件格式。
zlib可以压缩原始数据并输出gzip文件，gzip文件中除了压缩数据外，还有描述这些数据的文件头，所以当原始数据较小时，会出现zlib的压缩输出会比原始数据还大的情况。
/* 原始数据 */ unsigned char strSrc[] = "hello world! aaaaa 中文测试 哈哈哈~!@#$%^&*()_+yes"; unsigned long srcLen = sizeof(strSrc); printf("Src string:%s\nLength:%ld\n", strSrc, srcLen); /* 压缩 */ ::gzFile file = ::gzopen("d:/1.gz", "wb"); if (file != NULL) { printf("GZip file Writing ...\n"); ::gzwrite(file, strSrc, srcLen); printf("done.\n"); } ::gzclose(file);
如果想在内存中输出gzip格式的数据流，而不是写文件，则用以下方法：
/* Compress gzip data */ /* data 原数据 ndata 原数据长度 zdata 压缩后数据 nzdata 压缩后长度 */ int gzcompress(Bytef *data, uLong ndata, Bytef *zdata, uLong *nzdata) { z_stream c_stream; int err = 0; if (data && ndata > 0) { c_stream.zalloc = NULL; c_stream.zfree = NULL; c_stream.opaque = NULL; //只有设置为MAX_WBITS + 16才能在在压缩文本中带header和trailer if (deflateInit2(&c_stream, Z_DEFAULT_COMPRESSION, Z_DEFLATED, MAX_WBITS + 16, 8, Z_DEFAULT_STRATEGY) != Z_OK) return -1; c_stream.next_in = data; c_stream.avail_in = ndata; c_stream.next_out = zdata; c_stream.avail_out = *nzdata; while (c_stream.avail_in != 0 && c_stream.total_out < *nzdata) { if (deflate(&c_stream, Z_NO_FLUSH) != Z_OK) return -1; } if (c_stream.avail_in != 0) return c_stream.avail_in; for (;;) { if ((err = deflate(&c_stream, Z_FINISH)) == Z_STREAM_END) break; if (err != Z_OK) return -1; } if (deflateEnd(&c_stream) != Z_OK) return -1; *nzdata = c_stream.total_out; return 0; } return -1; } /* Uncompress gzip data */ /* zdata 数据 nzdata 原数据长度 data 解压后数据 ndata 解压后长度 */ int gzdecompress(Byte *zdata, uLong nzdata, Byte *data, uLong *ndata) { int err = 0; z_stream d_stream = { 0 }; /* decompression stream */ static char dummy_head[2] = { 0x8 + 0x7 * 0x10, (((0x8 + 0x7 * 0x10) * 0x100 + 30) / 31 * 31) & 0xFF, }; d_stream.zalloc = NULL; d_stream.zfree = NULL; d_stream.opaque = NULL; d_stream.next_in = zdata; d_stream.avail_in = 0; d_stream.next_out = data; //只有设置为MAX_WBITS + 16才能在解压带header和trailer的文本 if (inflateInit2(&d_stream, MAX_WBITS + 16) != Z_OK) return -1; //if(inflateInit2(&d_stream, 47) != Z_OK) return -1; while (d_stream.total_out < *ndata && d_stream.total_in < nzdata) { d_stream.avail_in = d_stream.avail_out = 1; /* force small buffers */ if ((err = inflate(&d_stream, Z_NO_FLUSH)) == Z_STREAM_END) break; if (err != Z_OK) { if (err == Z_DATA_ERROR) { d_stream.next_in = (Bytef*)dummy_head; d_stream.avail_in = sizeof(dummy_head); if ((err = inflate(&d_stream, Z_NO_FLUSH)) != Z_OK) { return -1; } } else return -1; } } if (inflateEnd(&d_stream) != Z_OK) return -1; *ndata = d_stream.total_out; return 0; }
以上这两种方法的输出都可以被java.util.zip.GZIPInputStream解压。
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原文地址：http://www.cnblogs.com/guoxiaoqian/p/4315195.html
