zlib 压缩，为什么不能用gzip解压？

s669pengwei 2012-01-18 11:28:12

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aijiumei 2012-01-31

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/*

00480 ZEXTERN int ZEXPORT deflateInit2 OF((z_streamp strm,

00481                                      int  level,

00482                                      int  method,

00483                                      int  windowBits,

00484                                      int  memLevel,

00485                                      int  strategy));

00486 

00487      This is another version of deflateInit with more compression options. The

00488    fields next_in, zalloc, zfree and opaque must be initialized before by

00489    the caller.

00490 

00491      The method parameter is the compression method. It must be Z_DEFLATED in

00492    this version of the library.

00493 

00494      The windowBits parameter is the base two logarithm of the window size

00495    (the size of the history buffer). It should be in the range 8..15 for this

00496    version of the library. Larger values of this parameter result in better

00497    compression at the expense of memory usage. The default value is 15 if

00498    deflateInit is used instead.

00499 

00500      windowBits can also be -8..-15 for raw deflate. In this case, -windowBits

00501    determines the window size. deflate() will then generate raw deflate data

00502    with no zlib header or trailer, and will not compute an adler32 check value.

00503 

00504      windowBits can also be greater than 15 for optional gzip encoding. Add

00505    16 to windowBits to write a simple gzip header and trailer around the

00506    compressed data instead of a zlib wrapper. The gzip header will have no

00507    file name, no extra data, no comment, no modification time (set to zero),

00508    no header crc, and the operating system will be set to 255 (unknown).  If a

00509    gzip stream is being written, strm->adler is a crc32 instead of an adler32.

00510 

00511      The memLevel parameter specifies how much memory should be allocated

00512    for the internal compression state. memLevel=1 uses minimum memory but

00513    is slow and reduces compression ratio; memLevel=9 uses maximum memory

00514    for optimal speed. The default value is 8. See zconf.h for total memory

00515    usage as a function of windowBits and memLevel.

00516 

00517      The strategy parameter is used to tune the compression algorithm. Use the

00518    value Z_DEFAULT_STRATEGY for normal data, Z_FILTERED for data produced by a

00519    filter (or predictor), Z_HUFFMAN_ONLY to force Huffman encoding only (no

00520    string match), or Z_RLE to limit match distances to one (run-length

00521    encoding). Filtered data consists mostly of small values with a somewhat

00522    random distribution. In this case, the compression algorithm is tuned to

00523    compress them better. The effect of Z_FILTERED is to force more Huffman

00524    coding and less string matching; it is somewhat intermediate between

00525    Z_DEFAULT and Z_HUFFMAN_ONLY. Z_RLE is designed to be almost as fast as

00526    Z_HUFFMAN_ONLY, but give better compression for PNG image data. The strategy

00527    parameter only affects the compression ratio but not the correctness of the

00528    compressed output even if it is not set appropriately.  Z_FIXED prevents the

00529    use of dynamic Huffman codes, allowing for a simpler decoder for special

00530    applications.

00531 

00532       deflateInit2 returns Z_OK if success, Z_MEM_ERROR if there was not enough

00533    memory, Z_STREAM_ERROR if a parameter is invalid (such as an invalid

00534    method). msg is set to null if there is no error message.  deflateInit2 does

00535    not perform any compression: this will be done by deflate().

00536 */

s669pengwei 2012-01-18

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我调用的是zlib里面的compress函数压缩，从内存在内存的，最后经过打包以后存到文件中，想再用linux自带的工具解压，不知道用什么可以

arfi 2012-01-18

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zip?
试一下 unzip

s669pengwei 2012-01-18

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[Quote=引用 7 楼 smallsmallsmallsmall 的回复:]

那你为什么不用gzip压缩，而选择自己实现呢？对压缩有什么特定的需求吗？

如果没有特定需求，就用system()直接调用gzip好了。
[/Quote]
要是用system，是不是只能对文件进行压缩？我希望是对内存中的buffer进行压缩，输出也为内存中的。

SmallSmallSmallSmall 2012-01-18